Associate Professor Bill Leggat
School of Environmental and Life Sciences
I am currently an Associate Professor in School of Environmental and Life Sciences. In this capacity, I am head of my own research group, the Symbiosis Genomics group in the Discipline of Environmental Sciences and Management, which focuses on understand the transcriptome and metabolome of the eukaryotic microbe Symbiodinium,their coral host and associated bacterial. My research aims to link transcriptional, proteomic and metabolomic changes in this holobiont to environmental change.
- Doctor of Philosophy, James Cook University
- Bachelor of Science (Biological Science), James Cook University
- Bachelor of Science (Honours), James Cook University
- Anthropogenic impacts
- Climate change
Fields of Research
|050101||Ecological Impacts of Climate Change||20|
|060702||Plant Cell and Molecular Biology||40|
|Title||Organisation / Department|
|Associate Professor||University of Newcastle
School of Environmental and Life Sciences
|Dates||Title||Organisation / Department|
|1/01/2014 - 1/12/2017||Associate Professor||James Cook University
Molecular and Cellular Biology
For publications that are currently unpublished or in-press, details are shown in italics.
Journal article (50 outputs)
Suggett DJ, Warner ME, Leggat W, 'Symbiotic Dinoflagellate Functional Diversity Mediates Coral Survival under Ecological Crisis', TRENDS IN ECOLOGY & EVOLUTION, 32 735-745 (2017)
Pontasch S, Fisher PL, Krueger T, Dove S, Hoegh-Guldberg O, Leggat W, Davy SK, 'Photoacclimatory and photoprotective responses to cold versus heat stress in high latitude reef corals', Journal of Phycology, 53 308-321 (2017)
© 2016 Phycological Society of America Corals at the world's southernmost coral reef of Lord Howe Island (LHI) experience large temperature and light fluctuations and need to... [more]
© 2016 Phycological Society of America Corals at the world's southernmost coral reef of Lord Howe Island (LHI) experience large temperature and light fluctuations and need to deal with periods of cold temperature ( < 18°C), but few studies have investigated how corals are able to cope with these conditions. Our study characterized the response of key photophysiological parameters, as well as photoacclimatory and photoprotective pigments (chlorophylls, xanthophylls, and ß-carotene), to short-term (5-d) cold stress (~15°C; 7°C below control) in three LHI coral species hosting distinct Symbiodinium ITS2 types, and compared the coral¿symbiont response to that under elevated temperature (~29°C; 7°C above control). Under cold stress, Stylophora sp. hosting Symbiodinium C118 showed the strongest effects with regard to losses of photochemical performance and symbionts. Pocillopora damicornis hosting Symbiodinium C100/C118 showed less severe bleaching responses to reduced temperature than to elevated temperature, while Porites heronensis hosting Symbiodinium C111* withstood both reduced and elevated temperature. Under cold stress, photoprotection in the form of xanthophyll de-epoxidation increased in unbleached P.¿heronensis (by 178%) and bleached Stylophora sp. (by 225%), while under heat stress this parameter increased in unbleached P.¿heronensis (by 182%) and in bleached P.¿damicornis (by 286%). The xanthophyll pool size was stable in all species at all temperatures. Our comparative study demonstrates high variability in the bleaching vulnerability of these coral species to low and high thermal extremes and shows that this variability is not solely determined by the ability to activate xanthophyll de-epoxidation.
Gierz SL, Forêt S, Leggat W, 'Transcriptomic analysis of thermally stressed Symbiodinium reveals differential expression of stress and metabolism genes', Frontiers in Plant Science, 8 (2017)
© 2017 Gierz, Forêt and Leggat. Endosymbioses between dinoflagellate algae (Symbiodinium sp.) and scleractinian coral species form the foundation of coral reef ecosystems. The cor... [more]
© 2017 Gierz, Forêt and Leggat. Endosymbioses between dinoflagellate algae (Symbiodinium sp.) and scleractinian coral species form the foundation of coral reef ecosystems. The coral symbiosis is highly susceptible to elevated temperatures, resulting in coral bleaching, where the algal symbiont is released from host cells. This experiment aimed to determine the transcriptional changes in cultured Symbiodinium, to better understand the response of cellular mechanisms under future temperature conditions. Cultures were exposed to elevated temperatures (average 31° C) or control conditions (24.5° C) for a period of 28 days. Whole transcriptome sequencing of Symbiodinium cells on days 4, 19, and 28 were used to identify differentially expressed genes under thermal stress. A large number of genes representing 37.01% of the transcriptome (~23,654 unique genes, FDR < 0.05) with differential expression were detected at no less than one of the time points. Consistent with previous studies of Symbiodinium gene expression, fold changes across the transcriptome were low, with 92.49% differentially expressed genes at =2-fold change. The transcriptional response included differential expression of genes encoding stress response components such as the antioxidant network and molecular chaperones, cellular components such as core photosynthesis machinery, integral light-harvesting protein complexes and enzymes such as fatty acid desaturases. Differential expression of genes encoding glyoxylate cycle enzymes were also found, representing the first report of this in Symbiodinium. As photosynthate transfer from Symbiodinium to coral hosts provides up to 90% of a coral¿s daily energy requirements, the implications of altered metabolic processes from exposure to thermal stress found in this study on coral-Symbiodinium associations are unknown and should be considered when assessing the stability of the symbiotic relationship under future climate conditions.
Ainsworth TD, Heron SF, Ortiz JC, Mumby PJ, Grech A, Ogawa D, et al., 'Climate change disables coral bleaching protection on the Great Barrier Reef', Science, 352 338-342 (2016)
© 2016, American Association for the Advancement of Science. All rights reserved. Coral bleaching events threaten the sustainability of the Great Barrier Reef (GBR). Here we show ... [more]
© 2016, American Association for the Advancement of Science. All rights reserved. Coral bleaching events threaten the sustainability of the Great Barrier Reef (GBR). Here we show that bleaching events of the past three decades have been mitigated by induced thermal tolerance of reef-building corals, and this protective mechanism is likely to be lost under near-future climate change scenarios. We show that 75% of past thermal stress events have been characterized by a temperature trajectory that subjects corals to a protective, sub-bleaching stress, before reaching temperatures that cause bleaching. Such conditions confer thermal tolerance, decreasing coral cell mortality and symbiont loss during bleaching by over 50%. We find that near-future increases in local temperature of as little as 0.5°C result in this protective mechanism being lost, which may increase the rate of degradation of the GBR.
Hernandez-Agreda A, Leggat W, Bongaerts P, Ainsworth TD, 'The microbial signature provides insight into the mechanistic basis of coral success across reef habitats', mBio, 7 (2016)
© 2016 Hernandez-Agreda et al. For ecosystems vulnerable to environmental change, understanding the spatiotemporal stability of functionally crucial symbioses is fundamental to de... [more]
© 2016 Hernandez-Agreda et al. For ecosystems vulnerable to environmental change, understanding the spatiotemporal stability of functionally crucial symbioses is fundamental to determining the mechanisms by which these ecosystems may persist. The coral Pachyseris speciosa is a successful environmental generalist that succeeds in diverse reef habitats. The generalist nature of this coral suggests it may have the capacity to form functionally significant microbial partnerships to facilitate access to a range of nutritional sources within different habitats. Here, we propose that coral is a metaorganism hosting three functionally distinct microbial interactions: a ubiquitous core microbiome of very few symbiotic host-selected bacteria, a microbiome of spatially and/or regionally explicit core microbes filling functional niches ( < 100 phylotypes), and a highly variable bacterial community that is responsive to biotic and abiotic processes across spatial and temporal scales ( > 100,000 phylotypes). We find that this coral hosts upwards of 170,000 distinct phylotypes and provide evidence for the persistence of a select group of bacteria in corals across environmental habitats of the Great Barrier Reef and Coral Sea. We further show that a higher number of bacteria are consistently associated with corals on mesophotic reefs than on shallow reefs. An increase in microbial diversity with depth suggests reliance by this coral on bacteria for nutrient acquisition on reefs exposed to nutrient upwelling. Understanding the complex microbial communities of host organisms across broad biotic and abiotic environments as functionally distinct microbiomes can provide insight into those interactions that are ubiquitous niche symbioses and those that provide competitive advantage within the hosts¿ environment.
Gierz SL, Gordon BR, Leggat W, 'Integral Light-Harvesting Complex Expression in Symbiodinium Within the Coral Acropora aspera under Thermal Stress', Scientific Reports, 6 (2016)
Coral reef success is largely dependent on the symbiosis between coral hosts and dinoflagellate symbionts belonging to the genus Symbiodinium. Elevated temperatures can result in ... [more]
Coral reef success is largely dependent on the symbiosis between coral hosts and dinoflagellate symbionts belonging to the genus Symbiodinium. Elevated temperatures can result in the expulsion of Symbiodinium or loss of their photosynthetic pigments and is known as coral bleaching. It has been postulated that the expression of light-harvesting protein complexes (LHCs), which bind chlorophylls (chl) and carotenoids, are important in photobleaching. This study explored the effect a sixteen-day thermal stress (increasing daily from 25-34 °C) on integral LHC (chlorophyll a-chlorophyll c 2-peridinin protein complex (acpPC)) gene expression in Symbiodinium within the coral Acropora aspera. Thermal stress leads to a decrease in Symbiodinium photosynthetic efficiency by day eight, while symbiont density was significantly lower on day sixteen. Over this time period, the gene expression of five Symbiodinium acpPC genes was quantified. Three acpPC genes exhibited up-regulated expression when corals were exposed to temperatures above 31.5 °C (acpPCSym-1:1, day sixteen; acpPCSym-15, day twelve; and acpPCSym-18, day ten and day sixteen). In contrast, the expression of acpPCSym-5:1 and acpPCSym-10:1 was unchanged throughout the experiment. Interestingly, the three acpPC genes with increased expression cluster together in a phylogenetic analysis of light-harvesting complexes.
van de Water JAJM, Leggat W, Bourne DG, van Oppen MJH, Willis BL, Ainsworth TD, 'Elevated seawater temperatures have a limited impact on the coral immune response following physical damage', Hydrobiologia, 759 201-214 (2015)
© 2015, Springer International Publishing Switzerland. Recurrent disturbances on coral reefs that cause injuries, like predation and storm damage, and elevated seawater temperatur... [more]
© 2015, Springer International Publishing Switzerland. Recurrent disturbances on coral reefs that cause injuries, like predation and storm damage, and elevated seawater temperatures reduce coral fitness and immunocompetence. An effective immune response is essential to prevent disease and enhance colony survival. To evaluate how elevated seawater temperatures affect the coral immune response following injury, fragments of Acropora aspera were exposed to ambient (27¿29°C) or elevated (32¿33.5°C) seawater temperatures for 8¿days and subsequently experimentally injured. Expression patterns for 15 immune genes 24¿h post-injury revealed that most genes involved in the Toll-like receptor pathway were unaffected by elevated seawater temperatures. Exceptions to this pattern were cFos and cJun, which were upregulated and likely played a role in repair processes, and TRAF-6 and NF¿B, which were downregulated suggesting reduced immune function. Components of the complement system were upregulated (millectin, C3) or downregulated (Bf, Tx60, apextrin) in corals at high temperatures. However, corals that also sustained injury, showed normal Tx60 and apextrin expression, suggesting roles in the wounding response. Overall, basal expression levels of immune genes are sufficient to mount a response to injury in the short term, and the immune response of A. aspera following injury is not significantly affected by minor elevations in seawater temperatures.
Ainsworth TD, Knack B, Ukani L, Seneca F, Weiss Y, Leggat W, 'In situ hybridisation detects pro-apoptotic gene expression of a Bcl-2 family member in white syndrome-affected coral', Diseases of Aquatic Organisms, 117 155-163 (2015)
© Inter-Research 2015. White syndrome has been described as one of the most prolific diseases on the Great Barrier Reef. Previously, apoptotic cell death has been described as the... [more]
© Inter-Research 2015. White syndrome has been described as one of the most prolific diseases on the Great Barrier Reef. Previously, apoptotic cell death has been described as the mechanism driving the characteristic rapid tissue loss associated with this disease, but the molecular mechanisms controlling apoptotic cell death in coral disease have yet to be investigated. In situ methods were used to study the expression patterns of 2 distinct regulators of apoptosis in Acropora hya cinthus tissues undergoing white syndrome and apoptotic cell death. Apoptotic genes within the Bcl-2 family were not localized in apparently healthy coral tissues. However, a Bcl-2 family member (bax-like) was found to localize to cells and tissues affected by white syndrome and those with morphological evidence for apoptosis. A potential up-regulation of pro-apoptotic or bax-like gene expression in tissues with apoptotic cell death adjacent to disease lesions is consistent with apoptosis being the primary cause of rapid tissue loss in coral affected by white syndrome. Pro-apoptotic (bax-like) expression in desmocytes and the basal tissue layer, the calicodermis, distant from the disease lesion suggests that apoptosis may also underlie the sloughing of healthy tissues associated with the characteristic, rapid spread of tissue loss, evident of this disease. This study also shows that in situ hybridisation is an effective tool for studying gene expression in adult corals, and wider application of these methods should allow a better understanding of many aspects of coral biology and disease pathology.
Van De Water JAJM, Ainsworth TD, Leggat W, Bourne DG, Willis BL, Van Oppen MJH, 'The coral immune response facilitates protection against microbes during tissue regeneration', Molecular Ecology, 24 3390-3404 (2015)
© 2015 John Wiley & Sons Ltd. Increasing physical damage on coral reefs from predation, storms and anthropogenic disturbances highlights the need to understand the impact of... [more]
© 2015 John Wiley & Sons Ltd. Increasing physical damage on coral reefs from predation, storms and anthropogenic disturbances highlights the need to understand the impact of injury on the coral immune system. In this study, we examined the regulation of the coral immune response over 10 days following physical trauma artificially inflicted on in situ colonies of the coral Acropora aspera, simultaneously with bacterial colonization of the lesions. Corals responded to injury by increasing the expression of immune system-related genes involved in the Toll-like and NOD-like receptor signalling pathways and the lectin-complement system in three phases ( < 2, 4 and 10 days post-injury). Phenoloxidase activity was also significantly upregulated in two phases ( < 3 and 10 days post-injury), as were levels of non-fluorescent chromoprotein. In addition, green fluorescent protein expression was upregulated in response to injury from 4 days post-injury, while cyan fluorescent protein expression was reduced. No shifts in the composition of coral-associated bacterial communities were evident following injury based on 16S rRNA gene amplicon pyrosequencing. Bacteria-specific fluorescence in situ hybridization also showed no evidence of bacterial colonization of the wound or regenerating tissues. Coral tissues showed near-complete regeneration of lesions within 10 days. This study demonstrates that corals exhibit immune responses that support rapid recovery following physical injury, maintain coral microbial homeostasis and prevent bacterial infestation that may compromise coral fitness.
Krueger T, Hawkins TD, Becker S, Pontasch S, Dove S, Hoegh-Guldberg O, et al., 'Differential coral bleaching-Contrasting the activity and response of enzymatic antioxidants in symbiotic partners under thermal stress', Comparative Biochemistry and Physiology -Part A : Molecular and Integrative Physiology, 190 15-25 (2015)
© 2015 Elsevier Inc. Mass coral bleaching due to thermal stress represents a major threat to the integrity and functioning of coral reefs. Thermal thresholds vary, however, betwee... [more]
© 2015 Elsevier Inc. Mass coral bleaching due to thermal stress represents a major threat to the integrity and functioning of coral reefs. Thermal thresholds vary, however, between corals, partly as a result of the specific type of endosymbiotic dinoflagellate (Symbiodinium sp.) they harbour. The production of reactive oxygen species (ROS) in corals under thermal and light stress has been recognised as one mechanism that can lead to cellular damage and the loss of their symbiont population (Oxidative Theory of Coral Bleaching). Here, we compared the response of symbiont and host enzymatic antioxidants in the coral species Acropora millepora and Montipora digitata at 28. °C and 33. °C. A. millepora at 33. °C showed a decrease in photochemical efficiency of photosystem II (PSII) and increase in maximum midday excitation pressure on PSII, with subsequent bleaching (declining photosynthetic pigment and symbiont density). M. digitata exhibited no bleaching response and photochemical changes in its symbionts were minor. The symbiont antioxidant enzymes superoxide dismutase, ascorbate peroxidase, and catalase peroxidase showed no significant upregulation to elevated temperatures in either coral, while only catalase was significantly elevated in both coral hosts at 33. °C. Increased host catalase activity in the susceptible coral after 5. days at 33. °C was independent of antioxidant responses in the symbiont and preceded significant declines in PSII photochemical efficiencies. This finding suggests a potential decoupling of host redox mechanisms from symbiont photophysiology and raises questions about the importance of symbiont-derived ROS in initiating coral bleaching.
Ainsworth TD, Krause L, Bridge T, Torda G, Raina JB, Zakrzewski M, et al., 'The coral core microbiome identifies rare bacterial taxa as ubiquitous endosymbionts', ISME Journal, 9 2261-2274 (2015)
© 2015 International Society for Microbial Ecology All rights reserved. Despite being one of the simplest metazoans, corals harbor some of the most highly diverse and abundant mic... [more]
© 2015 International Society for Microbial Ecology All rights reserved. Despite being one of the simplest metazoans, corals harbor some of the most highly diverse and abundant microbial communities. Differentiating core, symbiotic bacteria from this diverse hostassociated consortium is essential for characterizing the functional contributions of bacteria but has not been possible yet. Here we characterize the coral core microbiome and demonstrate clear phylogenetic and functional divisions between the micro-scale, niche habitats within the coral host. In doing so, we discover seven distinct bacterial phylotypes that are universal to the core microbiome of coral species, separated by thousands of kilometres of oceans. The two most abundant phylotypes are co-localized specifically with the corals' endosymbiotic algae and symbiont-containing host cells. These bacterial symbioses likely facilitate the success of the dinoflagellate endosymbiosis with corals in diverse environmental regimes.
Veilleux HD, Ryu T, Donelson JM, Van Herwerden L, Seridi L, Ghosheh Y, et al., 'Molecular processes of transgenerational acclimation to a warming ocean', Nature Climate Change, 5 1074-1078 (2015)
© 2015 Macmillan Publishers Limited. All rights reserved. Some animals have the remarkable capacity to acclimate across generations to projected future climate change; however, th... [more]
© 2015 Macmillan Publishers Limited. All rights reserved. Some animals have the remarkable capacity to acclimate across generations to projected future climate change; however, the underlying molecular processes are unknown. We sequenced and assembled de novo transcriptomes of adult tropical reef fish exposed developmentally or transgenerationally to projected future ocean temperatures and correlated the resulting expression profiles with acclimated metabolic traits from the same fish. We identified 69 contigs representing 53 key genes involved in thermal acclimation of aerobic capacity. Metabolic genes were among the most upregulated transgenerationally, suggesting shifts in energy production for maintaining performance at elevated temperatures. Furthermore, immune- and stress-responsive genes were upregulated transgenerationally, indicating a new complement of genes allowing the second generation of fish to better cope with elevated temperatures. Other differentially expressed genes were involved with tissue development and transcriptional regulation. Overall, we found a similar suite of differentially expressed genes among developmental and transgenerational treatments. Heat-shock protein genes were surprisingly unresponsive, indicating that short-term heat-stress responses may not be a good indicator of long-term acclimation capacity. Our results are the first to reveal the molecular processes that may enable marine fishes to adjust to a future warmer environment over multiple generations.
Krueger T, Fisher PL, Becker S, Pontasch S, Dove S, Hoegh-Guldberg O, et al., 'Transcriptomic characterization of the enzymatic antioxidants FeSOD, MnSOD, APX and KatG in the dinoflagellate genus Symbiodinium Genome evolution and evolutionary systems biology', BMC Evolutionary Biology, 15 (2015)
© 2015 Krueger et al.; licensee BioMed Central. Background: The diversity of the symbiotic dinoflagellate Symbiodinium sp., as assessed by genetic markers, is well established. To... [more]
© 2015 Krueger et al.; licensee BioMed Central. Background: The diversity of the symbiotic dinoflagellate Symbiodinium sp., as assessed by genetic markers, is well established. To what extent this diversity is reflected on the amino acid level of functional genes such as enzymatic antioxidants that play an important role in thermal stress tolerance of the coral-Symbiodinium symbiosis is, however, unknown. Here we present a predicted structural analysis and phylogenetic characterization of the enzymatic antioxidant repertoire of the genus Symbiodinium. We also report gene expression and enzymatic activity under short-term thermal stress in Symbiodinium of the B1 genotype. Results: Based on eight different ITS2 types, covering six clades, multiple protein isoforms for three of the four investigated antioxidants (ascorbate peroxidase [APX], catalase peroxidase [KatG] , manganese superoxide dismutase [MnSOD]) are present in the genus Symbiodinium. Amino acid sequences of both SOD metalloforms (Fe/Mn), as well as KatG, exhibited a number of prokaryotic characteristics that were also supported by the protein phylogeny. In contrast to the bacterial form, KatG in Symbiodinium is characterized by extended functionally important loops and a shortened C-terminal domain. Intercladal sequence variations were found to be much higher in both peroxidases, compared to SODs. For APX, these variable residues involve binding sites for substrates and cofactors, and might therefore differentially affect the catalytic properties of this enzyme between clades. While expression of antioxidant genes was successfully measured in Symbiodinium B1, it was not possible to assess the link between gene expression and protein activity due to high variability in expression between replicates, and little response in their enzymatic activity over the three-day experimental period. Conclusions: The genus Symbiodinium has a diverse enzymatic antioxidant repertoire that has similarities to prokaryotes, potentially as a result of horizontal gene transfer or events of secondary endosymbiosis. Different degrees of sequence evolution between SODs and peroxidases might be the result of potential selective pressure on the conserved molecular function of SODs as the first line of defence. In contrast, genetic redundancy of hydrogen peroxide scavenging enzymes might permit the observed variations in peroxidase sequences. Our data and successful measurement of antioxidant gene expression in Symbiodinium will serve as basis for further studies of coral health.
Voolstra CR, Miller DJ, Ragan MA, Hoffmann AA, Hoegh-Guldberg O, Bourne DG, et al., 'The ReFuGe 2020 Consortium-using "omics" approaches to explore the adaptability and resilience of coral holobionts to environmental change', Frontiers in Marine Science, 2 (2015)
© 2015 ReFuGe 2020 Consortium. Human-induced environmental changes have been linked directly with loss of biodiversity. Coral reefs, which have been severely impacted by anthropog... [more]
© 2015 ReFuGe 2020 Consortium. Human-induced environmental changes have been linked directly with loss of biodiversity. Coral reefs, which have been severely impacted by anthropogenic activities over the last few decades, exemplify this global problem and provide an opportunity to develop research addressing key knowledge gaps through "omics"-based approaches. While many stressors, e.g., global warming, ocean acidification, overfishing, and coastal development have been identified, there is an urgent need to understand how corals function at a basic level in order to conceive strategies for mitigating future reef loss. In this regard, availability of fully sequenced genomes has been immensely valuable in providing answers to questions of organismal biology. Given that corals are metaorganisms comprised of the coral animal host, its intracellular photosynthetic algae, and associated microbiota (i.e., bacteria, archaea, fungi, viruses), these efforts must focus on entire coral holobionts. The Reef Future Genomics 2020 (ReFuGe 2020) Consortium has formed to sequence hologenomes of 10 coral species representing different physiological or functional groups to provide foundation data for coral reef adaptation research that is freely available to the research community.
Krueger T, Becker S, Pontasch S, Dove S, Hoegh-Guldberg O, Leggat W, et al., 'Antioxidant plasticity and thermal sensitivity in four types of Symbiodinium sp.', Journal of Phycology, 50 1035-1047 (2014)
© 2014 Phycological Society of America Warmer than average summer sea surface temperature is one of the main drivers for coral bleaching, which describes the loss of endosymbiotic... [more]
© 2014 Phycological Society of America Warmer than average summer sea surface temperature is one of the main drivers for coral bleaching, which describes the loss of endosymbiotic dinoflagellates (genus: Symbiodinium) in reef-building corals. Past research has established that oxidative stress in the symbiont plays an important part in the bleaching cascade. Corals hosting different genotypes of Symbiodinium may have varying thermal bleaching thresholds, but changes in the symbiont's antioxidant system that may accompany these differences have received less attention. This study shows that constitutive activity and up-regulation of different parts of the antioxidant network under thermal stress differs between four Symbiodinium types in culture and that thermal susceptibility can be linked to glutathione redox homeostasis. In Symbiodinium B1, C1 and E, declining maximum quantum yield of PSII (F v /F m ) and death at 33°C were generally associated with elevated superoxide dismutase (SOD) activity and a more oxidized glutathione pool. Symbiodinium F1 exhibited no decline in F v /F m or growth, but showed proportionally larger increases in ascorbate peroxidase (APX) activity and glutathione content (GSx), while maintaining GSx in a reduced state. Depressed growth in Symbiodinium B1 at a sublethal temperature of 29°C was associated with transiently increased APX activity and glutathione pool size, and an overall increase in glutathione reductase (GR) activity. The collapse of GR activity at 33°C, together with increased SOD, APX and glutathione S-transferase activity, contributed to a strong oxidation of the glutathione pool with subsequent death. Integrating responses of multiple components of the antioxidant network highlights the importance of antioxidant plasticity in explaining type-specific temperature responses in Symbiodinium.
Chua CM, Leggat W, Moya A, Baird AH, 'Temperature affects the early life history stages of corals more than near future ocean acidification', Marine Ecology Progress Series, 475 85-92 (2013)
Climate change is projected to increase ocean temperatures by at least 2°C, and levels of pH by ~0.2 units (ocean acidification, OA) by the end of this century. While the effects ... [more]
Climate change is projected to increase ocean temperatures by at least 2°C, and levels of pH by ~0.2 units (ocean acidification, OA) by the end of this century. While the effects of these stressors on marine organisms have been relatively well explored in isolation, possible interactions between temperature and OA have yet to be thoroughly investigated. OA at levels projected to occur within this century has few direct ecological effects on the early life history stages of corals. In contrast, temperature has pronounced effects on many stages in the early life history of corals. Here, we test whether temperature might act in combination with OA to produce a measurable ecological effect on fertilization, development, larval survivorship or metamorphosis of 2 broadcast spawning species, Acropora millepora and A. tenuis, from the Great Barrier Reef. We used 4 treatments: control, high temperature (+2°C), high partial pressure of CO 2 (pCO 2 ) (700 µatm) and a combination of high temperature and high pCO 2 , corresponding to the current levels of these variables and the projected values for the end of this century under the IPCC A2 scenario. We found no consistent effect of elevated pCO 2 on fertilization, development, survivorship or metamorphosis, neither alone nor in combination with temperature. In contrast, a 2°C rise in temperature increased rates of development, but otherwise had no consistent effect on fertilization, survivorship or metamorphosis. We conclude that OA is unlikely to be a direct threat to the early life history stages of corals, at least in the near future. In contrast, rising sea temperatures are likely to affect coral population dynamics by increasing the rate of larval development with resulting changes in patterns of connectivity. © Inter-Research 2013.
Chua CM, Leggat W, Moya A, Baird AH, 'Near-future reductions in pH will have no consistent ecological effects on the early life-history stages of reef corals', Marine Ecology Progress Series, 486 143-151 (2013)
Until recently, research into the consequences of oceanic uptake of CO 2 for corals focused on its effect on physiological processes, in particular, calcification. However, even... [more]
Until recently, research into the consequences of oceanic uptake of CO 2 for corals focused on its effect on physiological processes, in particular, calcification. However, events early in the life history of corals are also likely to be vulnerable to changes in ocean chemistry caused by increases in the atmospheric concentration of CO 2 (ocean acidification). We tested the effect of reduced pH on embryonic development, larval survivorship and metamorphosis of 3 common scleractinian corals from the Great Barrier Reef. We used 4 treatment levels of pH, corresponding to the current level of ocean pH and 3 values projected to occur later this century. None of the early life-history stages we studied were consistently affected by reduced pH. Our results suggest that there will be no direct ecological effects of ocean acidification on the early life-history stages of reef corals, at least in the near future. © Inter-Research 2013 · www.int-res.com.
Ogawa D, Bobeszko T, Ainsworth T, Leggat W, 'The combined effects of temperature and CO
This study explored the interactive effects of near-term CO 2 increases (40-90 ppm above current ambient) during a simulated bleaching event (34 °C for 5 d) of Acropora aspera by ... [more]
This study explored the interactive effects of near-term CO 2 increases (40-90 ppm above current ambient) during a simulated bleaching event (34 °C for 5 d) of Acropora aspera by linking physiology to expression patterns of genes involved in carbon metabolism. Symbiodinium photosynthetic efficiency (F v /F m ) was significantly depressed by the bleaching event, while elevated pressure of CO 2 (pCO 2 ) slightly mitigated the effects of increased temperature on F v /F m during the final 4 d of the recovery period, however, did not affect the loss of symbionts. Elevated pCO 2 alone had no effect on F v /F m or symbiont density. Expression of targeted Symbiodinium genes involved in carbon metabolism and heat stress response was not significantly altered by either increased temperature and/or CO 2 . Of the selected host genes, two carbonic anhydrase isoforms (coCA2 and coCA3) exhibited the largest changes, most notably in crossed bleaching and elevated pCO 2 treatments. CA2 was significantly down-regulated on day 14 in all treatments, with the greatest decrease in the crossed treatment (relative expression compared to control = 0.16; p < 0.05); CA3 showed a similar trend, with expression levels 0.20-fold of controls on day 14 (p < 0.05) in the elevated temperature/pCO 2 treatment. The synergistic effects of ocean acidification and bleaching were evident during this study and demonstrate that increased pCO 2 in surface waters will impact corals much sooner than many studies utilising end-of-century pCO 2 concentrations would indicate. © 2013 Springer-Verlag Berlin Heidelberg.
Gordon BR, Leggat W, Motti CA, 'Extraction protocol for nontargeted NMR and LC-MS metabolomics-based analysis of hard coral and their algal symbionts', Methods in Molecular Biology, 1055 129-147 (2013)
Metabolomics and in particular, nontargeted metabolomics, has become a popular technique for the study of biological samples as it provides considerable amounts of information on ... [more]
Metabolomics and in particular, nontargeted metabolomics, has become a popular technique for the study of biological samples as it provides considerable amounts of information on extractable metabolites and is ideal for studying the metabolic response of an organism to stressors in its environment. One such organism, the symbiotic hard coral, presents its own complexity when considering a metabolomics approach in that it forms intricate associations with an array of symbiotic macro- and microbiota. While not discounting the importance of these many associations to the function of the coral holobiont, the coral-Symbiodinium relationship has been the most studied to date and as such, is the primary focus of this extraction protocol. This protocol provides details for the sample collection, extraction, and measurement of hard coral holobiont metabolites using both 1 H nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography coupled with mass spectrometry (LC-MS). Using this nontargeted metabolomics approach, the holobiont metabolism can be investigated for perturbations resulting from either (1) natural or anthropogenic environmental challenges, (2) the controlled application of stressors, and (3) differences between phenotypes or species. Consequently, this protocol will benefit both environmental and natural products based research of hard coral and their algal symbionts. Every effort has been made to provide the reader with all the details required to perform this protocol, including many of the costly and time consuming "pitfalls" or "traps" that were discovered during its development. As a result, this protocol can be confidently accomplished by those with less experience in the extraction and analysis of symbiotic hard coral, requiring minimal user input whilst ensuring reproducible and reliable results using readily available lab ware and reagents. © 2013 Springer Science+Business Media, LLC.
Gordon BR, Leggat W, Motti CA, 'Extraction protocol for nontargeted NMR and LC-MS metabolomics-based analysis of hard coral and their algal symbionts', Methods in Molecular Biology, 1055 129-147 (2013)
Metabolomics and in particular, nontargeted metabolomics, has become a popular technique for the study of biological samples as it provides considerable amounts of information on ... [more]
Metabolomics and in particular, nontargeted metabolomics, has become a popular technique for the study of biological samples as it provides considerable amounts of information on extractable metabolites and is ideal for studying the metabolic response of an organism to stressors in its environment. One such organism, the symbiotic hard coral, presents its own complexity when considering a metabolomics approach in that it forms intricate associations with an array of symbiotic macro- and microbiota. While not discounting the importance of these many associations to the function of the coral holobiont, the coral-Symbiodinium relationship has been the most studied to date and as such, is the primary focus of this extraction protocol. This protocol provides details for the sample collection, extraction, and measurement of hard coral holobiont metabolites using both < sup > 1 < /sup > H nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography coupled with mass spectrometry (LC-MS). Using this nontargeted metabolomics approach, the holobiont metabolism can be investigated for perturbations resulting from either (1) natural or anthropogenic environmental challenges, (2) the controlled application of stressors, and (3) differences between phenotypes or species. Consequently, this protocol will benefit both environmental and natural products based research of hard coral and their algal symbionts. Every effort has been made to provide the reader with all the details required to perform this protocol, including many of the costly and time consuming "pitfalls" or "traps" that were discovered during its development. As a result, this protocol can be confidently accomplished by those with less experience in the extraction and analysis of symbiotic hard coral, requiring minimal user input whilst ensuring reproducible and reliable results using readily available lab ware and reagents. © 2013 Springer Science+Business Media, LLC.
Rosic NN, Leggat W, Kaniewska P, Dove S, Hoegh-Guldberg O, 'New-old hemoglobin-like proteins of symbiotic dinoflagellates', Ecology and Evolution, 3 822-834 (2013)
Symbiotic dinoflagellates are unicellular photosynthetic algae that live in mutualistic symbioses with many marine organisms. Within the transcriptome of coral endosymbionts Symbi... [more]
Symbiotic dinoflagellates are unicellular photosynthetic algae that live in mutualistic symbioses with many marine organisms. Within the transcriptome of coral endosymbionts Symbiodinium sp. (type C3), we discovered the sequences of two novel and highly polymorphic hemoglobin-like genes and proposed their 3D protein structures. At the protein level, four isoforms shared between 87 and 97% sequence identity for Hb-1 and 78-99% for Hb-2, whereas between Hb-1 and Hb-2 proteins, only 15-21% sequence homology has been preserved. Phylogenetic analyses of the dinoflagellate encoding Hb sequences have revealed a separate evolutionary origin of the discovered globin genes and indicated the possibility of horizontal gene transfer. Transcriptional regulation of the Hb-like genes was studied in the reef-building coral Acropora aspera exposed to elevated temperatures (6-7°C above average sea temperature) over a 24-h period and a 72-h period, as well as to nutrient stress. Exposure to elevated temperatures resulted in an increased Hb-1 gene expression of 31% after 72¿h only, whereas transcript abundance of the Hb-2 gene was enhanced by up to 59% by both 1-day and 3-day thermal stress conditions. Nutrient stress also increased gene expression of Hb-2 gene by 70%. Our findings describe the differential expression patterns of two novel Hb genes from symbiotic dinoflagellates and their polymorphic nature. Furthermore, the inducible nature of Hb-2 gene by both thermal and nutrient stressors indicates a prospective role of this form of hemoglobin in the initial coral-algal responses to changes in environmental conditions. This novel hemoglobin has potential use as a stress biomarker. © 2013 The Authors. Ecology and Evolution.
Boldt L, Yellowlees D, Leggat W, 'Hyperdiversity of Genes Encoding Integral Light-Harvesting Proteins in the Dinoflagellate Symbiodinium sp', PLoS ONE, 7 (2012)
The superfamily of light-harvesting complex (LHC) proteins is comprised of proteins with diverse functions in light-harvesting and photoprotection. LHC proteins bind chlorophyll (... [more]
The superfamily of light-harvesting complex (LHC) proteins is comprised of proteins with diverse functions in light-harvesting and photoprotection. LHC proteins bind chlorophyll (Chl) and carotenoids and include a family of LHCs that bind Chl a and c. Dinophytes (dinoflagellates) are predominantly Chl c binding algal taxa, bind peridinin or fucoxanthin as the primary carotenoid, and can possess a number of LHC subfamilies. Here we report 11 LHC sequences for the chlorophyll a-chlorophyll c 2 -peridinin protein complex (acpPC) subfamily isolated from Symbiodinium sp. C3, an ecologically important peridinin binding dinoflagellate taxa. Phylogenetic analysis of these proteins suggests the acpPC subfamily forms at least three clades within the Chl a/c binding LHC family; Clade 1 clusters with rhodophyte, cryptophyte and peridinin binding dinoflagellate sequences, Clade 2 with peridinin binding dinoflagellate sequences only and Clades 3 with heterokontophytes, fucoxanthin and peridinin binding dinoflagellate sequences. © 2012 Boldt et al.
Leggat W, Yellowlees D, Medina M, 'Recent progress in Symbiodinium transcriptomics', Journal of Experimental Marine Biology and Ecology, 408 120-125 (2011)
Dinoflagellate symbionts of the genus Symbiodinium are integral to the success of the coral holobiont (a coral host and the microbial community it harbours), however despite their... [more]
Dinoflagellate symbionts of the genus Symbiodinium are integral to the success of the coral holobiont (a coral host and the microbial community it harbours), however despite their importance we currently have a very limited knowledge of the genes which they possess and their genomic organisation. Analysis shows that the number of expressed sequence tags (genes that are expressed) available for Symbiodinium (7964) is less than 1/10 of those available for the scleractinian coral host (103,434). This lack of DNA sequence information limits the functional genomic studies that can be undertaken from the symbiont perspective. In addition these sequences are from only three Symbiodinium types (C3, A1, A3) and do not represent the large diversity of clades and subclades seen. Here we summarise our current understanding of the Symbiodinium genomic content with reference to our knowledge of other dinoflagellates. The genetic information of Symbiodinium is encompassed in the nuclear, plastid and mitochondrial genomes. As is the case with other dinoflagellates these three genomes are significantly different from the "general" phototrophic eukaryote. Firstly the nuclear genome of dinoflagellates is extremely large, utilises modified DNA bases not normally found in eukaryotes, and tandem repeat regions seem to contain the most highly expressed genes. Meanwhile the plastid genome, which normally contains between 40 and 250 genes in other eukaryotes, has been reduced t o 18 genes encoded in "minicircles." Finally the dinoflagellate mitochondrial genome only encodes for 2 or 3 proteins instead of the normal 40-50 in other eukaryotes. While we have some knowledge of Symbiodinium genome structure, little is known about its transcriptome. With the advent of inexpensive high throughput sequencing technologies, our understanding of the Symbiodinium genome will rapidly increase and we will begin to be able to look into the responses of these important single celled organisms. © 2011 Elsevier B.V.
Leggat W, Seneca F, Wasmund K, Ukani L, Yellowlees D, Ainsworth TD, 'Differential responses of the coral host and their algal symbiont to thermal stress', PLoS ONE, 6 (2011)
The success of any symbiosis under stress conditions is dependent upon the responses of both partners to that stress. The coral symbiosis is particularly susceptible to small incr... [more]
The success of any symbiosis under stress conditions is dependent upon the responses of both partners to that stress. The coral symbiosis is particularly susceptible to small increases of temperature above the long term summer maxima, which leads to the phenomenon known as coral bleaching, where the intracellular dinoflagellate symbionts are expelled. Here we for the first time used quantitative PCR to simultaneously examine the gene expression response of orthologs of the coral Acropora aspera and their dinoflagellate symbiont Symbiodinium. During an experimental bleaching event significant up-regulation of genes involved in stress response (HSP90 and HSP70) and carbon metabolism (glyceraldehyde-3-phosphate dehydrogenase, a-ketoglutarate dehydrogenase, glycogen synthase and glycogen phosphorylase) from the coral host were observed. In contrast in the symbiont, HSP90 expression decreased, while HSP70 levels were increased on only one day, and only the a-ketoglutarate dehydrogenase expression levels were found to increase. In addition the changes seen in expression patterns of the coral host were much larger, up to 10.5 fold, compared to the symbiont response, which in all cases was less than 2-fold. This targeted study of the expression of key metabolic and stress genes demonstrates that the response of the coral and their symbiont vary significantly, also a response in the host transcriptome was observed prior to what has previously been thought to be the temperatures at which thermal stress events occur. © 2011 Leggat et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Ainsworth TD, Wasmund K, Ukani L, Seneca F, Yellowlees D, Miller D, Leggat W, 'Defining the tipping point. A complex cellular life/death balance in corals in response to stress', Scientific Reports, 1 (2011)
Apoptotic cell death has been implicated in coral bleaching but the molecules involved and the mechanisms by which apoptosis is regulated are only now being identified. In contras... [more]
Apoptotic cell death has been implicated in coral bleaching but the molecules involved and the mechanisms by which apoptosis is regulated are only now being identified. In contrast the mechanisms underlying apoptosis in higher animals are relatively well understood. To better understand the response of corals to thermal stress, the expression of coral homologs of six key regulators of apoptosis was studied in Acropora aspera under conditions simulating those of a mass bleaching event. Significant changes in expression were detected between the daily minimum and maximum temperatures. Maximum daily temperatures from as low as 3°C below the bleaching threshold resulted in significant changes in both pro-and anti-apoptotic gene expression. The results suggest that the control of apoptosis is highly complex in this eukaryote-eukaryote endosymbiosis and that apoptotic cell death cascades potentially play key roles tipping the cellular life/death balance during environmental stress prior to the onset of coral bleaching.
Kvennefors ECE, Leggat W, Kerr CC, Ainsworth TD, Hoegh-Guldberg O, Barnes AC, 'Analysis of evolutionarily conserved innate immune components in coral links immunity and symbiosis', Developmental and Comparative Immunology, 34 1219-1229 (2010)
Reef-building corals are representatives of one of the earliest diverging metazoan lineages and are experiencing increases in bleaching events (breakdown of the coral-. Symbiodini... [more]
Reef-building corals are representatives of one of the earliest diverging metazoan lineages and are experiencing increases in bleaching events (breakdown of the coral-. Symbiodinium symbiosis) and disease outbreaks. The present study investigates the roles of two pattern recognition proteins, the mannose binding lectin Millectin and a complement factor C3-like protein (C3-Am), in the coral Acropora millepora. The results indicate that the innate immune functions of these molecules are conserved and arose early in evolution. C3-Am is expressed in response to injury, and may function as an opsonin. In contrast, Millectin expression is up-regulated in response to lipopolysaccharide and peptidoglycan. These observations, coupled with localization of Millectin in nematocysts in epidermal tissue, and reported binding of pathogens, are consistent with a key role for the lectin in innate immunity. Furthermore, Millectin was consistently detected binding to the symbiont Symbiodinium in vivo, indicating that the Millectin function of recognition and binding of non-self-entities may have been co-opted from an ancient innate immune system into a role in symbiosis. © 2010 Elsevier Ltd.
Gordon BR, Leggat W, 'Symbiodinium - Invertebrate symbioses and the role of metabolomics', Marine Drugs, 8 2546-2568 (2010)
Symbioses play an important role within the marine environment. Among the most well known of these symbioses is that between coral and the photosynthetic dinoflagellate, Symbiodin... [more]
Symbioses play an important role within the marine environment. Among the most well known of these symbioses is that between coral and the photosynthetic dinoflagellate, Symbiodinium spp. Understanding the metabolic relationships between the host and the symbiont is of the utmost importance in order to gain insight into how this symbiosis may be disrupted due to environmental stressors. Here we summarize the metabolites related to nutritional roles, diel cycles and the common metabolites associated with the invertebrate-Symbiodinium relationship. We also review the more obscure metabolites and toxins that have been identified through natural products and biomarker research. Finally, we discuss the key role that metabolomics and functional genomics will play in understanding these important symbioses. © 2010 by the authors; licensee MDPI.
Reef R, Dunn S, Levy O, Dove S, Shemesh E, Bhckner I, et al., 'Photoreactivation is the main repair pathway for UV-induced DNA damage in coral planulae', Journal of Experimental Biology, 212 2760-2766 (2009)
The larvae of most coral species spend some time in the plankton, floating just below the surface and hence exposed to high levels of ultraviolet radiation (UVRThe high levels of ... [more]
The larvae of most coral species spend some time in the plankton, floating just below the surface and hence exposed to high levels of ultraviolet radiation (UVRThe high levels of UVR are potentially stressful and damaging to DNA and other cellular components, such as proteins, reducing survivorship. Consequently, mechanisms to either shade (prevent) or repair damage potentially play an important role. In this study, the role of photoreactivation in the survival of coral planulae was examined. Photoreactivation is a light-stimulated response to UV-damaged DNA in which photolyase proteins repair damaged DNA. Photoreactivation rates, as well as the localization of photolyase, were explored in planulae under conditions where photoreactivation was or was not inhibited. The results indicate that photoreactivation is the main DNA repair pathway in coral planulae, repairing UV-induced DNA damage swiftly (K=1.75h -1 and a half-life of repair of 23 min), with no evidence of any light-independent DNA repair mechanisms, such as nucleotide excision repair (NER), at work. Photolyase mRNA was localized to both the ectoderm and endoderm of the larvae. The amount of cell death in the coral planulae increased significantly when photoreactivation was inhibited, by blocking photoreactivating light. We found that photoreactivation, along with additional UV shielding in the form of five mycosporine-like amino acids, are sufficient for survival in surface tropical waters and that planulae do not accumulate DNA damage despite being exposed to high UVR.
Voolstra CR, Sunagawa S, Schwarz JA, Coffroth MA, Yellowlees D, Leggat W, Medina M, 'Evolutionary analysis of orthologous cDNA sequences from cultured and symbiotic dinoflagellate symbionts of reef-building corals (Dinophyceae: Symbiodinium)', Comparative Biochemistry and Physiology - Part D: Genomics and Proteomics, 4 67-74 (2009)
Dinoflagellates are ubiquitous marine and freshwater protists. The endosymbiotic relationship between dinoflagellates of the genus Symbiodinium (also known as zooxanthellae) and c... [more]
Dinoflagellates are ubiquitous marine and freshwater protists. The endosymbiotic relationship between dinoflagellates of the genus Symbiodinium (also known as zooxanthellae) and corals forms the basis of coral reefs. We constructed and analyzed a cDNA library from a cultured Symbiodinium species clade A (CassKB8). The majority of annotated ESTs from the Symbiodinium sp. CassKB8 library cover metabolic genes. Most of those belong to either carbohydrate or energy metabolism. In addition, components of extracellular signal transduction pathways and genes that play a role in cell-cell communication were identified. In a subsequent analysis, we determined all orthologous cDNA sequences between this library (1,484 unique sequences) and a library from a Symbiodinium species clade C (C3) (3,336 unique sequences) that was isolated directly from its symbiotic host. A set of 115 orthologs were identified between Symbiodinium sp. CassKB8 and Symbiodinium sp. C3. These orthologs were subdivided into three groups that show different characteristics and functions: conserved across eukaryotes (CE), dinoflagellate-specific (DS) and Symbiodinium-specific (SS). Orthologs conserved across eukaryotes are mainly comprised of housekeeping genes, photosynthesis-related transcripts and metabolic proteins, whereas the function for most of the dinoflagellate-specific orthologs remains unknown. A dN/dS analysis identified the highest ratio in a Symbiodinium-specific ortholog and evidence for positive selection in a dinoflagellate-specific gene. Evolution of genes and pathways in different dinoflagellates seems to be affected by different lifestyles, and a symbiotic lifestyle may affect population structure and strength of selection. This study is the first evolutionary comparative analysis of orthologs from two coral dinoflagellate symbionts. © 2008 Elsevier Inc. All rights reserved.
Middlebrook R, Hoegh-Guldberg O, Leggat W, 'The effect of thermal history on the susceptibility of reef-building corals to thermal stress', Journal of Experimental Biology, 211 1050-1056 (2008)
The mutualistic relationship between corals and their unicellular dinoflagellate symbionts (Symbiodinium sp.) is a fundamental component within the ecology of coral reefs. Thermal... [more]
The mutualistic relationship between corals and their unicellular dinoflagellate symbionts (Symbiodinium sp.) is a fundamental component within the ecology of coral reefs. Thermal stress causes the breakdown of the relationship between corals and their symbionts (bleaching). As with other organisms, this symbiosis may acclimate to changes in the environment, thereby potentially modifying the environmental threshold at which they bleach. While a few studies have examined the acclimation capacity of reef-building corals, our understanding of the underlying mechanism is still in its infancy. The present study focused on the role of recent thermal history in influencing the response of both corals and symbionts to thermal stress, using the reef-building coral Acropora aspera. The symbionts of corals that were exposed to 31°C for 48 h (pre-stress treatment) 1 or 2 weeks prior to a 6-day simulated bleaching event (when corals were exposed to 34°C) were found to have more effective photoprotective mechanisms. These mechanisms included changes in non-photochemical quenching and xanthophyll cycling. These differences in photoprotection were correlated with decreased loss of symbionts, with those corals that were not prestressed performing significantly worse, losing over 40% of their symbionts and having a greater reduction in photosynthetic efficiency. These results are important in that they show that thermal history, in addition to light history, can influence the response of reef-building corals to thermal stress and therefore have implications for the modeling of bleaching events. However, whether acclimation is capable of modifying the thermal threshold of corals sufficiently to cope as sea temperatures increase in response to global warming has not been fully explored. Clearly increases in sea temperatures that extend beyond 1-2°C will exhaust the extent to which acclimation can modify the thermal threshold of corals.
Ainsworth TD, Hoegh-Guldberg O, Heron SF, Skirving WJ, Leggat W, 'Early cellular changes are indicators of pre-bleaching thermal stress in the coral host', Journal of Experimental Marine Biology and Ecology, 364 63-71 (2008)
Thermal stress causes the coral-dinoflagellate symbiosis to disassociate and the coral tissues to whiten. The onset and occurrence of this coral bleaching is primarily defined via... [more]
Thermal stress causes the coral-dinoflagellate symbiosis to disassociate and the coral tissues to whiten. The onset and occurrence of this coral bleaching is primarily defined via the dinoflagellate responses. Here we demonstrate that thermal stress responses occur in the coral host tissues in the days before the onset of coral bleaching. The observed sequence of thermal responses includes reductions in thickness of coral tissue layers and apoptosis of the cells prior to reductions in symbiont density. In the days before the onset of coral bleachi ng the outer coral tissue layer (epithelium) thickness reduces and apoptosis occurs within the gastrodermis. Two days following this, coinciding with an initial reduction of symbiont density (by approximately 25%), gastrodermal thickness decreased and apoptosis of host cells was identified in the epithelium. This was eventually followed by large reduction in symbiont density (by approximately 50%) consistent with coral bleaching. Both pro-apoptotic and anti-apoptotic genes are identified in the reef building coral Acropora aspera, demonstrating the necessary pathways are present for fine control of host apoptosis. Our study shows that defining periods of host stress based on the responses defined by dinoflagellate symbiont underestimates the importance of early cellular events and the cellular complexity of coral host. © 2008 Elsevier B.V.
Ainsworth TD, Hoegh-Guldberg O, Leggat W, 'Imaging the fluorescence of marine invertebrates and their associated flora', Journal of Microscopy, 232 197-199 (2008)
The cells and tissues of many marine invertebrates and their associated flora contain fluorescent pigments and proteins, many of which have been utilized commercially and provide ... [more]
The cells and tissues of many marine invertebrates and their associated flora contain fluorescent pigments and proteins, many of which have been utilized commercially and provide marker molecules in other systems for fluorescence imaging technology. However, in the study of marine invertebrates and their symbioses these naturally occurring molecules have been seen to limit or confound fluorescence microscopy analyses. Here we demonstrate the endogenous fluorescence associated with two marine invertebrates (coral and foraminifera) and describe how these qualities can be utilized in fluorescence microanalyses. Understanding and imaging the diversity of fluorescent molecules provide insight into how fluorescence microscopy techniques can now be applied to these complex systems. © 2008 The Authors.
Yellowlees D, Rees TAV, Leggat W, 'Metabolic interactions between algal symbionts and invertebrate hosts', Plant, Cell and Environment, 31 679-694 (2008)
Some invertebrates have enlisted autotrophic unicellular algae to provide a competitive metabolic advantage in nutritionally demanding habitats. These symbioses exist primarily bu... [more]
Some invertebrates have enlisted autotrophic unicellular algae to provide a competitive metabolic advantage in nutritionally demanding habitats. These symbioses exist primarily but not exclusively in shallow tropical oceanic waters where clear water and low nutrient levels provide maximal advantage to the association. Mostly, the endosymbiotic algae are localized in host cells surrounded by a host-derived membrane (symbiosome). This anatomy has required adaptation of the host biochemistry to allow transport of the normally excreted inorganic nutrients (CO 2 , NH 3 and PO 4 3- ) to the alga. In return, the symbiont supplies photosynthetic products to the host to meet its energy demands. Most attention has focused on the metabolism of CO 2 and nitrogen sources. Carbon-concentrating mechanisms are a feature of all algae, but the products exported to the host following photosynthetic CO 2 fixation vary. Identification of the stimulus for release of algal photosynthate in hospite remains elusive. Nitrogen assimilation within the symbiosis is an essential element in the host's control over the alga. Recent studies have concentrated on cnidarians because of the impact of global climate change resulting in coral bleaching. The loss of the algal symbiont and its metabolic contribution to the host has the potential to result in the transition from a coral-dominated to an algal-dominated ecosystem. © 2008 The Authors.
Kvennefors ECE, Leggat W, Hoegh-Guldberg O, Degnan BM, Barnes AC, 'An ancient and variable mannose-binding lectin from the coral Acropora millepora binds both pathogens and symbionts', Developmental and Comparative Immunology, 32 1582-1592 (2008)
Corals form the framework of the world's coral reefs and are under threat from increases in disease and bleaching (symbiotic dysfunction), yet the mechanisms of pathogen and ... [more]
Corals form the framework of the world's coral reefs and are under threat from increases in disease and bleaching (symbiotic dysfunction), yet the mechanisms of pathogen and symbiont recognition remain largely unknown. Here we describe the isolation and characterisation of an ancient mannose-binding lectin in the coral Acropora millepora, which is likely to be involved in both processes. The lectin ('Millectin') was isolated by affinity chromatography and was shown to bind to bacterial pathogens as well as coral symbionts, dinoflagellates of the genus Symbiodinium. cDNA analysis of Millectin indicate extensive sequence variation in the binding region, reflecting its ability to recognise various mannose-like carbohydrate structures on non-self cells, including symbionts and pathogens. This is the first mannose-binding lectin to show extensive sequence variability as observed for pattern recognition proteins in other invertebrate immune systems and, given that invertebrates rely on non-adaptive immunity, is a potential keystone component of coral defence mechanisms. © 2008 Elsevier Ltd. All rights reserved.
Leggat W, Hoegh-Guldberg O, Dove S, Yellowlees D, 'Analysis of an EST library from the dinoflagellate (Symbiodinium sp.) symbiont of reef-building corals', Journal of Phycology, 43 1010-1021 (2007)
Dinoflagellates (Symbiodinium sp. Freud.) are an obligatory endosymbiont of the reef-building corals. Recent changes to the environment surrounding coral reefs (e.g., global warmi... [more]
Dinoflagellates (Symbiodinium sp. Freud.) are an obligatory endosymbiont of the reef-building corals. Recent changes to the environment surrounding coral reefs (e.g., global warming) have demonstrated that this endosymbiotic relationship between corals and Symbiodinium is particularly sensitive to environmental changes. Therefore, understanding gene expression patterns of Symbiodinium is critical to understanding why coral reefs are susceptible to global climate change. This study identified 1456 unique expression sequence tags (ESTs) generated for Symbiodinium (clade C3) from the staghorn coral Acropora aspera following exposure to a variety of stresses. Of these, only 10% matched previously reported dinoflagellate ESTs, suggesting that the conditions used in the construction of the library resulted in a novel transcriptome. The function of 561 (44%) of these ESTs could be identified. The majority of these genes coded for proteins involved in posttranslational modification, protein turnover, and chaperones (12.3%); energy production and conversion (12%); or an unknown function (18.6%). The most common transcript found was a homologue to a bacterial protein of unknown function. This algal protein is targeted to the chloroplast and is present in those phototrophs that acquired plastids from the red algal lineage. An additional 48 prokaryote-like proteins were also identified, including the first glycerol-phosphate:phosphate antiporter from dinoflagellates. A protein with similarity to the fungi-archael-bacterial heme catalase peroxidases was also found. A variety of stress genes, in particular heat-shock proteins and proteins involved in ubiquitin cascades, were also identified. This study is the first transcriptome from the unicellular component of a eukaryote-eukaryote symbiosis. © 2007 Phycological Society of America.
Levy O, Appelbaum L, Leggat W, Gothlif Y, Hayward DC, Miller DJ, Hoegh-Guldberg O, 'Light-responsive cryptochromes from a simple multicellular animal, the coral Acropora millepora', Science, 318 467-470 (2007)
Hundreds of species of reef-building corals spawn synchronously over a few nights each year, and moonlight regulates this spawning event. However, the molecular elements underpinn... [more]
Hundreds of species of reef-building corals spawn synchronously over a few nights each year, and moonlight regulates this spawning event. However, the molecular elements underpinning the detection of moonlight remain unknown. Here we report the presence of an ancient family of blue-light-sensing photoreceptors, cryptochromes, in the reef-building coral Acropora millepora. In addition to being cryptochrome genes from one of the earliest-diverging eumetazoan phyla, cry1 and cry2 were expressed preferentially in light. Consistent with potential roles in the synchronization of fundamentally important behaviors such as mass spawning, cry2 expression increased on full moon nights versus new moon nights. Our results demonstrate phylogenetically broad roles of these ancient circadian clock-related molecules in the animal kingdom.
Yarden O, Ainsworth TD, Roff G, Leggat W, Fine M, Hoegh-Guldberg O, 'Increased prevalence of ubiquitous ascomycetes in an acropoid coral (Acropora formosa) exhibiting symptoms of brown band syndrome and skeletal eroding band disease', Applied and Environmental Microbiology, 73 2755-2757 (2007)
The prevalence of coral-associated fungi was four times higher in diseased Acropora formosa colonies than in healthy colonies. Since taxonomically related fungal species were isol... [more]
The prevalence of coral-associated fungi was four times higher in diseased Acropora formosa colonies than in healthy colonies. Since taxonomically related fungal species were isolated from diseased and healthy colonies, we suggest that their association with coral may be constitutive but that their abundance is dependent on coral health. Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Baird AH, Cumbo VR, Leggat W, Rodriguez-Lanetty M, 'Fidelity and flexibility in coral symbioses', Marine Ecology Progress Series, 347 307-309 (2007)
Understanding whether or not corals have the flexibility to change their complement of symbionts to adapt to changing climate is an important goal in reef ecology studies. While h... [more]
Understanding whether or not corals have the flexibility to change their complement of symbionts to adapt to changing climate is an important goal in reef ecology studies. While host fidelity to a single clade of symbiont is the dominant pattern in present-day corals, current estimates of flexibility are unreliable, because few studies have measured it rigorously and with adequately sensitive genetic techniques. Furthermore, flexibility must be explored at the level of the subclade, because generalisations of physiological performance among clades of Symbiodinium are not valid. In addition, we should not necessarily expect to see shifts among symbionts without distinct and enduring changes in environmental conditions. The few biogeographical comparisons available suggest that when corals encounter a new environment they have the flexibility to acquire different symbionts. Flexibility in the acquisition of symbionts is common at the time of infection, which in most corals occurs at, or shortly after, settlement. Consequently, flexibility is likely to be a feature of the life history of all species that must reacquire symbionts in each new generation. © Inter-Research 2007.
Leggat W, Ainsworth T, Bythell J, Dove S, Gates R, Hoegh-Guldberg O, et al., 'The hologenome theory disregards the coral holobiont', Nature Reviews Microbiology, 5 (2007)
Leggat W, Ainsworth TD, Dove S, Hoegh-Guldberg O, 'Aerial exposure influences bleaching patterns', Coral Reefs, 25 452 (2006)
Edmunds PJ, Gates RD, Leggat W, Hoegh-Guldberg O, Allen-Requa L, 'The effect of temperature on the size and population density of dinoflagellates in larvae of the reef coral Porites astreoides', Invertebrate Biology, 124 185-193 (2005)
Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typical... [more]
Pre-settlement events play an important role in determining larval success in marine invertebrates with bentho-pelagic life histories, yet the consequences of these events typically are not well understood. The purpose of this study was to examine the pre-settlement impacts of different seawater temperatures on the size and population density of dinoflagellate symbionts in brooded larvae of the Caribbean coral Porites astreoides. Larvae were collected from P. astreoides at 14-20m depth on Conch Reef (Florida) in June 2002, and incubated for 24 h at 15 temperatures spanning the range 25.1°-30.0°C in mean increments of 0.4 ± 0.1°C (± SD). The most striking feature of the larval responses was the magnitude of change in both parameters across this 5°C temperature range within 24 h. In general, larvae were largest and had the highest population densities of Symbiodinium sp. between 26.4°-27.7°C, and were smallest and had the lowest population densities at 25.8°C and 28.8°C. Larval size and symbiont population density were elevated slightly (relative to the minimal values) at the temperature extremes of 25.1°C and 30°C. These data demonstrate that coral larvae are highly sensitive to seawater temperature during their pelagic phase, and respond through changes in size and the population densities of Symbiodinium sp. to ecologically relevant temperature signals within 24 h. The extent to which these changes are biologically meaningful will depend on the duration and frequency of exposure of coral larvae to spatiotemporal variability in seawater temperature, and whether the responses have cascading effects on larval success and their entry to the post-settlement and recruitment phase. © 2005 American Microscopical Society, Inc.
Leggat W, Dixon R, Saleh S, Yellowlees D, 'A novel carbonic anhydrase from the giant clam Tridacna gigas contains two carbonic anhydrase domains', FEBS Journal, 272 3297-3305 (2005)
This report describes the presence of a unique dual domain carbonic anhydrase (CA) in the giant clam, Tridacna gigas. CA plays an important role in the movement of inorganic carbo... [more]
This report describes the presence of a unique dual domain carbonic anhydrase (CA) in the giant clam, Tridacna gigas. CA plays an important role in the movement of inorganic carbon (C i ) from the surrounding seawater to the symbiotic algae that are found within the clam's tissue. One of these isoforms is a glycoprotein which is significantly larger (70 kDa) than any previously reported from animals (generally between 28 and 52 kDa). This a-family CA contains two complete carbonic anhydrase domains within the one protein, accounting for its large size; dual domain CAs have previously only been reported from two algal species. The protein contains a leader sequence, an N-terminal CA domain and a C-terminal CA domain. The two CA domains have relatively little identity at the amino acid level (29%). The genomic sequence spans in excess of 17 kb and contains at least 12 introns and 13 exons. A number of these introns are in positions that are only found in the membrane attached/secreted CAs. This fact, along with phylogenetic analysis, suggests that this protein represents the second example of a membrane attached invertebrate CA and it contains a dual domain structure unique amongst all animal CAs characterized to date. © 2005 FEBS.
Leggat W, Buck BH, Grice A, Yellowlees D, 'The impact of bleaching on the metabolic contribution of dinoflagellate symbionts to their giant clam host', Plant, Cell and Environment, 26 1951-1961 (2003)
Bleaching (loss of symbiotic dinoflagellates) is known to significantly decrease the fitness of symbiotic marine invertebrates resulting in reduced growth, fecundity and survival.... [more]
Bleaching (loss of symbiotic dinoflagellates) is known to significantly decrease the fitness of symbiotic marine invertebrates resulting in reduced growth, fecundity and survival. This report is the first to quantify the effects of bleaching on inorganic carbon (C 1 ) and ammonium flux, fixation and export of photosynthate to the host, in this case the giant clam Tridacna gigas. The 1998 bleaching event was found to decrease the zooxanthellae population 30-fold when comparing bleached to non-bleached clams. This resulted in significant increases in haemolymph C 1 and decreases in haemolymph pH and glucose concentration, the predominant photosynthate exported from zooxanthellae in this symbiosis. There was also a decrease in the expression levels of host carbonic anhydrase, an enzyme involved in C 1 transport to the zooxanthellae, and although host glutamine synthase levels were unaffected, the clams ability to assimilate ammonium was eliminated in bleached individuals, suggesting that photosynthate from the zooxanthellae is required for ammonium assimilation. In an artificial bleaching experiment haemolymph C i (r 2 = 0.97), pH (r 2 = 0.94) and glucose levels (r 2 = 0.95) were correlated to zooxanthellae numbers during both bleaching and recovery. Recovery of the zooxanthellae population, was enhanced four-fold by the addition of organic and inorganic nutrients, as were related haemolymph characteristics. These results highlight the profound physiological changes that occur in symbiotic organisms during and after a bleaching event.
Leggat W, Rees TAV, Yellowlees D, 'Meeting the photosynthetic demand for inorganic carbon in an alga-invertebrate association: Preferential use of CO
Unlike most marine invertebrates which excrete respiratory CO 2 , giant clams (Tridacna gigas) must acquire inorganic carbon (C(i)) in order to support their symbiotic population ... [more]
Unlike most marine invertebrates which excrete respiratory CO 2 , giant clams (Tridacna gigas) must acquire inorganic carbon (C(i)) in order to support their symbiotic population of photosynthetic dinoflagellates. Their capacity to meet this demand will be reflected in the C(i) concentration of their haemolymph during periods of high photosynthesis. The C(i) concentration in haemolymph was found to be inversely proportional to irradiance with a minimum C(i) concentration of 0.75 mM at peak light levels increasing to 1.2 mM in the dark. The photosynthetic rate of isolated zooxanthellae under conditions that prevail in the haemolymph at peak light levels was significantly less than the potential P(max) (maximum photosynthetic rate) indicating that zooxanthellae are carbon limited in hospite. This is consistent with previous studies on the hermatypic coral symbiosis. The P(max) was not affected by pH but there was a dramatic increase in the half-saturation constant for C(i) (k 0.5 (C(i))) with increasing pH (6.5-9.0) and only a small decrease in k 0.5 (CO 2 ) over the same range. These results indicate that zooxanthellae in giant clams use CO 2 as the primary source of their C(i) in contrast to symbionts in corals, which use bicarbonate. The physiological implications are discussed and comparison is made with the coral symbiosis.
Shepherd D, Leggat W, Rees TAV, Yellowlees D, 'Ammonium, but not nitrate, stimulates an increase in glutamine concentration in the haemolymph of Tridacna gigas', Marine Biology, 133 45-53 (1999)
The concentration of glutamine in Tridacna gigas haemolymph increased > 35-fold following exposure to sea water supplemented with ammonium (20 µM), but no increase was observ... [more]
The concentration of glutamine in Tridacna gigas haemolymph increased > 35-fold following exposure to sea water supplemented with ammonium (20 µM), but no increase was observed with nitrate (20 µM). Lack of a diel cycle, no decrease in haemolymph glucose levels, the expression patterns of glutamine synthetase in zooxanthellae and host, and the lack of glutamine release in response to nitrate supplementation all support the proposition that the increase in haemolymph glutamine is a product of the host and not the zooxanthellae. Unlike ammonium, nitrate accumulates rapidly in the haemolymph. It has no effect on the concentration of glutamine in the haemolymph, but there is an increase in arginine, histidine and lysine in the haemolymph, suggesting the release of these essential amino acids from zooxanthellae. Glutamine synthetase (GS) activity decreased markedly in the gill and less so in the mantle over a period of 6 d exposure to elevated ammonium (20 µM). In contrast, GS activity in zooxanthellae doubled. The response of zooxanthellae in situ was confirmed by incubating freshly isolated zooxanthellae for 4 d in ammonium, which resulted in a ten-fold increase in GS activity. Comparison of the in situ response of zooxanthellae with that obtained in vitro indicates that the symbionts are likely to be exposed to ammonium concentrations lower than that found in the haemolymph.
Leggat W, Badger MR, Yellowlees D, 'Evidence for an inorganic carbon-concentrating mechanism in the symbiotic dinoflagellate Symbiodinium sp.', Plant Physiology, 121 1247-1255 (1999)
The presence of a carbon-concentrating mechanism in the symbiotic dinoflagellate Symbiodinium sp. was investigated. Its existence was postulated to explain how these algae fix ino... [more]
The presence of a carbon-concentrating mechanism in the symbiotic dinoflagellate Symbiodinium sp. was investigated. Its existence was postulated to explain how these algae fix inorganic carbon (C(i)) efficiently despite the presence of a form II Rubisco. When the dinoflagellates were isolated from their host, the giant clam (Tridacna gigas), CO 2 uptake was found to support the majority of net photosynthesis (45%-80%) at pH 8.0; however, 2 d after isolation this decreased to 5% to 65%, with HCO 3 - uptake supporting 35% to 95% of net photosynthesis. Measurements of intracellular C(i) concentrations showed that levels inside the cell were between two and seven times what would be expected from passive diffusion of C(i) into the cell. Symbiodinium also exhibits a distinct light-activated intracellular carbonic anhydrase activity. This, coupled with elevated intracellular C(i) and the ability to utilize both CO 2 and HCO 3 - from the medium, suggests that Symbiodinium sp. does possess a carbon-concentrating mechanism. However, intracellular C(i) levels are not as large as might be expected of an alga utilizing a form II Rubisco with a poor affinity for CO 2 .
Badger MR, Andrews TJ, Whitney SM, Ludwig M, Yellowlees DC, Leggat W, Price GD, 'The diversity and coevolution of Rubisco, plastids, pyrenoids, and chloroplast-based CO
Algae have adopted two primary strategies to maximize the performance of Rubisco in photosynthetic CO 2 fixation. This has included either the development of a CO 2 -concentratin... [more]
Algae have adopted two primary strategies to maximize the performance of Rubisco in photosynthetic CO 2 fixation. This has included either the development of a CO 2 -concentrating mechanism (CCM), based at the level of the chloroplast, or the evolution of the kinetic properties of Rubisco. This review examines the potential diversity of both Rubisco and chloroplast-based CCMs across algal divisions, including both green and nongreen algae, and seeks to highlight recent advances in our understanding of the area and future areas for research. Overall, the available data show that Rubisco enzymes from algae have evolved a higher affinity for CO 2 when the algae have adopted a strategy for CO 2 fixation that does not utilise a CCM. This appears to be true of both Green and Red Form I Rubisco enzymes found in green and nongreen algae, respectively. However, the Red Form I Rubisco enzymes present in nongreen algae appear to have reduced oxygenase potential at air level of O 2 . This has resulted in a photosynthetic physiology with a reduced potential to be inhibited by O 2 and a reduced need to deal with photorespiration. In the limited number of microalgae that have been examined, there is a strong correlation between the existence of a high-affinity CCM physiology and the presence of pyrenoids in all algae, highlighting the potential importance of these chloroplast Rubisco-containing bodies. However, in macroalgae, there is greater diversity in the apparent relationships between pyrenoids and chloroplast features and the CCM physiology that the species shows. There are many examples of microalgae and macroalgae with variations in the presence and absence of pyrenoids as well as single and multiple chloroplasts per cell. This occurs in both green and nongreen algae and should provide ample material for extending studies in this area. Future research into the function of the pyrenoid and other chloroplast features, such as thylakoids, in the operation of a chloroplast-based CCM needs to be addressed in a diverse range of algal species. This should be approached together with assessment of the coevolution of Rubisco, particularly the evolution of Red Form I Rubisco enzymes, which appear to achieve superior kinetic characteristics when compared with the Ruhisco of C 3 higher plants, which are derived from green algal ancestors.
Belda-Baillie CA, Leggat W, Yellowlees D, 'Growth and metabolic responses of the giant clamzooxanthellae symbiosis in a reef-fertilisation experiment', Marine Ecology Progress Series, 170 131-141 (1998)
To evaluate the impact of elevated nutrients on reef organisms symbiotic with zooxanthellae, giant clams Tridacna maxima were exposed daily to increased ammonia and phosphate (N, ... [more]
To evaluate the impact of elevated nutrients on reef organisms symbiotic with zooxanthellae, giant clams Tridacna maxima were exposed daily to increased ammonia and phosphate (N, P, N+P) in their natural reef environment for 3 to 6 mo. The results strongly corroborate the major responses of the symbiotic association to nutrient enrichment previously observed (with T. gigas) under controlled outdoor conditions. Exposure of the clams to elevated N (10 µM) increased zooxanthellae density, reduced zooxanthellae size, down-regulated N uptake by zooxanthellae freshly isolated from their hosts, and reduced glutamate in the clam haemolymph, with increased pools of some free amino acids (methionine, tyrosine) in the zooxanthellae. These results confirm that the zooxanthellae in giant clams are N limited in situ and have free access to inorganic N from the sea water. There is also corroborating evidence that the zooxanthellae are P limited in situ as well, possibly due to host interference. While the N:P ratios of the animal host reflected ambient N and P concentrations in the sea water, those of the zooxanthellae did not. Regardless of P exposure (2 µM P) of the clams, zooxanthellae N:P ratios were consistently high ( > 30:1) and phosphate concentrations in the clam haemolymph bathing the zooxanthellae tube system consistently low ( < 0.1 µM). These field findings, consistent with previous laboratory observations, confirm the limiting roles of both N and P in the giant clam-zooxanthellae symbiosis. That significant changes occurred earlier and at lower nutrient loading compared to some reef organisms investigated within the same experimental framework further demonstrates organism-level responses of a potential bio-indicator of the early onset of eutrophication in reef waters.
|Show 47 more journal articles|
Conference (2 outputs)
Leggat W, Whitney S, Yellowlees D, 'Is coral bleaching due to the instability of the zooxanthellae dark reactions?', Symbiosis (2004)
Coral reefs are dominated by symbioses between marine invertebrates (e.g. corals, clams, sea anemones, sponges) and the dinoflagellate Symbiodinium. Increases in seawater temperat... [more]
Coral reefs are dominated by symbioses between marine invertebrates (e.g. corals, clams, sea anemones, sponges) and the dinoflagellate Symbiodinium. Increases in seawater temperature linked to global warming have lead to the phenomenon known as "bleaching", involving the disassociation of these symbioses and mass mortalities of the invertebrate host. Mass bleaching events have been linked to a thermal lesion in the photosynthesis of Symbiodinium, either at photosystem II or in the dark reactions of photosynthesis. Examination of two of the proposed lesion points, the carbon concentrating mechanism (CCM) and form II Rubisco, indicate that, over the temperature range examined, the CCM is not disrupted in Symbiodinium isolated from giant clams, however it was not possible to determine if Rubisco is the point of thermal lesion resulting in bleaching. Maximum photosynthetic rates were measured between 28 and 31°C and declined as temperature was increased. Despite a low correlation between Rubisco activity, oxygen evolution and temperature, Rubisco activity declined with increasing temperature.
Leggat W, Marendy EM, Baillie B, Whitney SM, Ludwig M, Badger MR, Yellowlees D, 'Dinoflagellate symbioses: Strategies and adaptations for the acquisition and fixation of inorganic carbon', Functional Plant Biology (2002)
Dinoflagellates exist in symbiosis with a number of marine invertebrates including giant clams, which are the largest of these symbiotic organisms. The dinoflagellates (Symbiodini... [more]
Dinoflagellates exist in symbiosis with a number of marine invertebrates including giant clams, which are the largest of these symbiotic organisms. The dinoflagellates (Symbiodinium sp.) live intercellularly within tubules in the mantle of the host clam. The transport of inorganic carbon (Ci) from seawater to Symbiodinium (=zooxanthellae) is an essential function of hosts that derive the majority of their respiratory energy from the photosynthate exported by the zooxanthellae. Immunolocalisation studies show that the host has adapted its physiology to acquire, rather than remove CO 2 , from the haemolymph and clam tissues. Two carbonic anhydrase (CA) isoforms (32 and 70 kDa) play an essential part in this process. These have been localised to the mantle and gill tissues where they catalyse the interconversion of HCO 3 - to CO 2 , which then diffuses into the host tissues. The zooxanthellae exhibit a number of strategies to maximise Ci acquisition and utilisation. This is necessary as they express a form II Rubisco that has poor discrimination between CO 2 and O 2 . Evidence is presented for a carbon concentrating mechanism (CCM) to overcome this disadvantage. The CCM incorporates the presence of a light-activated CA activity, a capacity to take up both HCO 3 - and CO 2 , an ability to accumulate an elevated concentration of Ci within the algal cell, and localisation of Rubisco to the pyrenoid. These algae also express both external and intracellular CAs, with the intracellular isoforms being localised to the thylakoid lumen and pyrenoid. These results have been incorporated into a model that explains the transport of Ci from seawater through the clam to the zooxanthellae.
Grants and Funding
|Number of grants||4|
Click on a grant title below to expand the full details for that specific grant.
20182 grants / $156,136
Funding body: ARC (Australian Research Council)
|Funding body||ARC (Australian Research Council)|
|Project Team||Associate Professor Bill Leggat, Associate Professor Tracy Ainsworth, Professor Andrew Baird|
|Type Of Funding||Aust Competitive - Non Commonwealth|
Funding body: ARC (Australian Research Council)
|Funding body||ARC (Australian Research Council)|
|Project Team||Associate Professor Bill Leggat, Associate Professor David Suggett, Dr Tim Kahlke|
|Type Of Funding||Aust Competitive - Non Commonwealth|
20141 grants / $500,000
Funding body: Great Barrier Reef Foundation
|Funding body||Great Barrier Reef Foundation|
Leggat, W., Ainsworth, T., Gordon, B., Heron, S., Roessner, U., Grech, A. Rosenthal, N.
|Scheme||Great Barrier Reef Foundation|
|Type Of Funding||C3112 - Aust Not for profit|
20131 grants / $310,000
Advancing knowledge of microbial symbioses underpinning coral health and reef resilience and predicting their responses to climate change $310,000
Funding body: ARC (Australian Research Council)
|Funding body||ARC (Australian Research Council)|
Leggat, W., Willis, B, Ainsworth, TD, Bourne, D, Medina, M
|Type Of Funding||Aust Competitive - Commonwealth|
Number of supervisions
Total current UON EFTSL
|Commenced||Level of Study||Research Title||Program||Supervisor Type|
|2018||PhD||The Role of the Coral Microbiome in Structural Stability and Thermal Acclimation: Implications for the Future of the GBR Following the 2016/17 Mass Bleaching Event||PhD (Biological Sciences), Faculty of Science, The University of Newcastle||Principal Supervisor|
|2018||PhD||Predicting the Prevalence of Coral Disease in Two Pacific Ocean Coral Species||PhD (Marine Science), Faculty of Science, The University of Newcastle||Principal Supervisor|
The map is a representation of a researchers co-authorship with collaborators across the globe. The map displays the number of publications against a country, where there is at least one co-author based in that country. Data is sourced from the University of Newcastle research publication management system (NURO) and may not fully represent the authors complete body of work.
|Country||Count of Publications|