Dr Logeshwaran Panneerselvan

A Gram-positive bacterium, Microbacterium esteraromaticum MM1 able to degrade organophosphorus pesticides such as fenamiphos and malathion, also possessed the ability to degrade high molecular weight polycyclic aromatic hydrocarbon (PAH), pyrene (Pyr) and benzo[a]pyrene (BaP). The strain MM1 degraded 98.7% of initially spiked 100 mg L-1 pyrene within 15 days from the M9 mineral salts medium (pH 7.0) with 0.1% glucose. At optimal pH 7.0, 57.81% of pyrene (100 mg L-1) was degraded as the sole carbon source. In order to determine the influence of carbon sources (glucose, sodium acetate, sodium succinate) and PAHs (Naphthalene (Nap), Phenanthrene (Phe), Benzo[a]pyrene (BaP)) on pyrene degradation, a full factorial design analysis was conducted. Among the carbon sources examined, glucose, sodium acetate, and all the PAHs positively affected pyrene degradation. Interestingly, in the presence of other PAHs, benzo[a]pyrene was degraded by MM1 but not as the sole carbon source. Crude enzyme extracted from MM1 degraded pyrene with the Km and Vmax values of 49.3 µg ml-1 (equivalent to 250 µM) and 9.5 µg ml-1 min-1 mg-1 of crude protein (equivalent to 50 µM), respectively with a specific activity of 0.19 µg ml-1 mg-1 of crude protein. Metabolites such as monohydroxypyrene, 2,6-di-isopropylnaphthalene, and phthalic acid were identified during pyrene degradation by MM1. Differential expression of the protein in the presence of pyrene resulted in the inducement of enolase (phosphopyruvate hydratase) and pyridine nucleotide-disulphide oxidoreductase in MM1. To the best of our knowledge, this is the first report on the degradation of pyrene by M. esteraromaticum MM1.

Acid soils are the degraded (nutrient-poor) soils that generally lack microbial abundance required to promote plant growth. An insight into the microbial diversity in highly acidic soils is crucial from both ecological and environmental standpoints. Previously, we showed that inoculation of acid soils with acid-tolerant microalgae (algalization) significantly improved soil physicochemical and biological characteristics. In the present novel study involving a laboratory microcosm, high-throughput 16S rRNA amplicon sequencing analysis was performed to investigate the bacterial diversity in acid soils algalized with Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3 after 90 days of incubation. Our results on pooled DNA demonstrate that algalization of two acid soils (soil A and B) significantly increased several bacterial genera, and this observation is consistent with Shannon and Chao1 diversity indices. Actinobacteria, Acidobacteria, Firmicutes, and Proteobacteria were the most prevalent phyla enriched in all of the algalized treatments. Interestingly, nonalgalized acid soils favored only Firmicutes and Actinobacteria, but algalization significantly enriched Proteobacteria, Acidobacteria, and Actinobacteria. Canonical correspondence analysis revealed a positive effect of pH in soil A and both pH and organic carbon in soil B on enrichment. Furthermore, soil bacteria of ecological significance that belong to rhizobacteria and diazotrophs, such as Acetobacter, Azospirillum, Bradyrhizobium, Gluconacetobacter, Nitrobacter, Burkholderia, Comamonas, Herbaspirillum, Enterobacter, Nitrosococcus, Brevibacillus, Enterococcus, Frankia, and Anabaena, were greatly enriched in algalized treatments. Thus, we demonstrate here for the first time that algalization of acid soils significantly improves soil health through enrichment of bacteria that are largely implicated in promoting soil health and plant growth

In developing and developed countries, urban gardening has increasingly become an integral part of local food systems for good quality produce, for enhanced urban health and sustainability. There are few gardens with naturally perfect soils for growing plants. However, the soils with poor texture and fewer nutrients can be improved by different types of organic amendments such as composts, garden soils and organic potting mixes that are commercially available in the consumer markets worldwide to promote healthy plant growth. In this study, we assessed 19 different commercially available composts, garden soils, and potting mixes for the presence of 38 per- and polyfluoroalkyl substances (PFAS). The total (¿38) PFAS in the samples ranged between 1.26 to 11.84 µg kg-1 (dry weight). The total concentration of perfluorinated carboxylic acids (¿PFCAs) was higher than that of perfluoroalkyl sulfonic acids (PFSAs) in all products. The total oxidizable precursor assay (TOPA) was applied in the analysis of composts and potting mixes, which revealed an increase in short-chain ¿PFCAs concentrations ranging from 0.48 to 7.63 µg kg-1, which suggested the transformation of PFCAs precursors to short-chain PFCAs. The measured concentrations of short-chain PFCAs after TOPA in the soil substrates have the potential to contribute to plant uptake and food chain transfer of PFAS to humans due to their high mobility.

Pyroligneous acid (PA) is often used in agriculture as a plant growth and yield enhancer. However, the influence of PA application on soil microorganisms is not often studied. Therefore, in this study, we investigated the effect of PA (0.01¿5% w/w in soil) on the microbial diversity in two different soils. At the end of eight weeks of incubation, soil microbial community dynamics were determined by Illumina-MiSeq sequencing of 16S rRNA gene amplicons. The microbial composition differed between the lower (0.01% and 0.1%) and the higher (1% and 5%) concentration in both PA spiked soils. The lower concentration of PA resulted in higher microbial diversity and dehydrogenase activity (DHA) compared to the un-spiked control and the soil spiked with high PA concentrations. Interestingly, PA-induced plant growth-promoting bacterial (PGPB) genera include Bradyrhizobium, Azospirillum, Pseudomonas, Mesorhizobium, Rhizobium, Herbaspiriluum, Acetobacter, Beijerinckia, and Nitrosomonas at lower concentrations. Additionally, the PICRUSt functional analysis revealed the predominance of metabolism as the functional module¿s primary component in both soils spiked with 0.01% and 0.1% PA. Overall, the results elucidated that PA application in soil at lower concentrations promoted soil DHA and microbial enrichment, particularly the PGPB genera, and thus have great implications for improving soil health.

Widespread environmental contamination of per- and polyfluoroalkyl substances (PFAS) is well established. Nevertheless, few studies have reported on the aquatic toxicity of PFAS, especially in indicator species such as Daphnia. In this study, the toxicity of two major PFAS, namely perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS), was investigated on water flea (Daphnia carinata) using a battery of comprehensive toxicity tests, including a 48 h acute and a 21-day chronic assays. The survival, growth, and reproduction of D. carinata were monitored over a 21-day life cycle. PFOS exhibited higher toxicity than PFOA. The 48 h LC50 values (confidence interval) based on acute toxicity for PFOA and PFOS were 78.2 (54.9¿105) mg L-1 and 8.8 (6.4¿11.6) mg L-1, respectively. Chronic exposure to PFOS for 21 days displayed mortality and reproductive defects in D. carinata at a concentration as low as 0.001 mg L-1. Genotoxicity assessment using comet assay revealed that exposure for 96 h to PFOS at 1 and 10.0 mg L-1 significantly damaged the organism's genetic makeup. The results of this study have great implications for risk assessment of PFOS and PFOA in aquatic ecosystems, given the potential of PFOS to pose a risk to Daphnia even at lower concentrations (1 µg L-1).

Perfluorooctanoic acid (PFOA) is a prevalent, persistent organic pollutant (POP) in the environment. The potential toxic impacts of PFOA on human and ecological health is becoming an increasing concern worldwide. In this study, we investigated the acute toxicity of PFOA in terms of growth, mortality, lifespan, neurobehaviour, fecundity and livelihood in Caenorhabditis elegans (C. elegans), a free-living ecologically important animal model species. The acute toxicity (LC50) of PFOA was found to be 4.42 µM (1.83 mg/L). PFOA exposure induced alteration in locomotor behaviour in C. elegans. The reproduction capacity of C. elegans was also reduced after exposure to 0.1 µM (41.4 µg/L) PFOA. Similarly, developmental toxicity was also documented with the reduction in lifespan and alteration in chemotaxis plasticity above 1 µM (414 µg/L) PFOA. C. elegans bioaccumulated PFOA about 520 times than the surrounding concentration when exposed to 0.41 ug/L PFOA. Given that PFOA has demonstrated its toxicological impacts on the reproductive capacity and lifespan of C. elegans at the concentrations that are commonly found at contaminated areas, it is likely that the contamination of PFOA will have detrimental effects on the food chain in both terrestrial and aquatic ecosystems. Thus, the results of this study have significant implications for the ecological risk assessment and remediation of PFOA.

Perfluorobutane sulfonate (PFBS), due to its increasing use as an alternative to perfluooctane sulfonate (PFOS), is widely detected in humans and the environment, necessitating the evaluation of its potential ecotoxicological risk. We assessed the toxicity and bioaccumulation potential of PFBS in Caenorhabditis elegans, using lethality, locomotion, reproduction, life span, growth, and chemotactic behavior as the effect parameters. In addition, a total of 6 generations of exposed parent animals were monitored for locomotion, brood, and life span behaviors. Life span and brood size were significantly reduced in parent nematodes (P0) following exposure to =0.1 mM PFBS, but these negative effects did not transfer to the progeny. Although there was no remarkable effect on reproduction and life span in parent worms exposed to =0.01 mM PFBS, multigenerational exposure at 0.0005 mM significantly affected the F4 and F5 progeny. Furthermore, 0.01 to 2.0 mM of PFBS substantially retarded the locomotion behavior of P0 worms. At higher concentrations such as 1.0 mM, this negative effect on locomotion was transferred to the next generation (F1) but later recovered from F2 progeny onward. Our findings demonstrate for the first time that chronic exposure to PFBS at higher concentrations can cause behavioral toxicity and could be transferred to the progeny. These findings have significant implications for the environmental risk assessment of PFBS. Environ Toxicol Chem 2021;40:1973¿1982. © 2021 SETAC.

Worldwide a multitude of firefighting compounds are currently used for the mitigation and protection of man-made structures and forests alike from fire damages. Among the class of firefighting agents, Class B firefighting foams are generally used to control fires generated from hydrocarbon liquids. In the present study, we assessed the cyto- and genotoxicity of two widely used class B firefighting foam concentrates, Tridol-S 3% and Tridol-S 6% to Alliumcepa through chromosomal aberration and comet assay using root meristem cells. A. cepa root tips were exposed to Tridol-S 3% and Tridol-S 6% with six different concentrations (0%, 0.005%, 0.01%, 0.02%, 0.03%, 0.04% and 0.05%) for 24 h. Cytogenetic effect endpoints such as mitotic index, and chromosomal aberrations were observed. Chromosomal aberrations in the control (untreated onion root tips) was negligible with the mitotic index (MI) value of 79.6%, while the MI significantly decreased in all the test concentrations of firefighting compounds. Genotoxicity assessment through comet assay also revealed that both the products were genotoxic with a significant increase in per cent tail DNA and olive tail moment. Among the test compounds, Tridol-S 3% was more toxic than Tridol-S 6%. To our knowledge, this is the first study on the cyto- and genotoxic effects of class B firefighting foams to A. cepa root meristem cells. This study also suggests that the toxicological studies using A. cepa root meristem cells can be employed for evaluating the toxicological impacts of firefighting foams in the environment.