Dr Mezbaul Bahar

An arsenic hyper-tolerant diazotrophic bacterium was isolated from a heavy metal contaminated soil. The pure isolate MM-17 was identified as Azospirillum sp. based on phylogenetic analysis of 16S rRNA. The strain oxidized 100 µM As(III) to As(V) in both culture media (minimal salts) and real groundwater within 8 and 10 h, respectively. The oxidation of As(III) by this strain was observed within the pH range 5-10 with the best performance at pH 7-8. As(III) oxidation was found to be independent of cell growth which implies the oxidation enzymes are constitutively expressed. The whole cell kinetic study highlighted a lower value of kinetic constant, Ks as 32.9 µM As(III), which indicates that the strain MM-17 has greater affinity for As(III). The gene sequence of the large subunit of arsenite oxidase of MM-17 showed 99 and 72% similarity to the large subunit of arsenite oxidase of Stenotrophomonas sp. MM-7 and Sinorhizobium sp. M14, respectively. Sphaeroplasts experiments suggest that arsenite oxidase is a membrane associated protein in MM-17.

In this study, the toxicity, biotransformation and bioaccumulation of arsenite and arsenate in a soil microalga, Chlorella sp., were investigated using different phosphate levels. The results indicated that arsenate was highly toxic than arsenite to the alga, and the phosphate limitation in growth media greatly enhanced arsenate toxicity. The uptake of arsenate in algal cells was more than that of arsenite, and the predominant species in the growth media was arsenate after 8¿days of exposure to arsenite or arsenate, indicating arsenite oxidation by this microalga. Arsenate reduction was also observed when the alga was incubated in a phosphate-limiting growth medium. Similar to the process of biotransformation, the alga accumulated more arsenic when it was exposed to arsenate and preferably more in a phosphate-limiting condition. Although phosphate significantly influences the biotransformation and bioaccumulation of arsenic, the oxidizing ability and higher accumulation capacity of this alga have great potential for its application in arsenic bioremediation.

Arsenic contamination of groundwater and surface water is widespread throughout the world. Considering its carcinogenicity and toxicity to human and animal health, remediation of arsenic-contaminated water has become a high priority. There are several physicochemical-based conventional technologies available for removing arsenic from water. However, these technologies possess a number of limitations such as high cost and generation of toxic by-products, etc. Therefore, research on new sustainable and cost-effective arsenic removal technologies for water has recently become an area of intense research activity. Bioremediation technology offers great potential for possible future application in decontamination of pollutants from the natural environment. It is not only environmentally friendly but cost-effective as well. This review focuses on the state-of-art knowledge of currently available arsenic remediation methods, their prospects, and recent advances with particular emphasis on bioremediation strategies. © 2013 Springer Science+Business Media Dordrecht.

The involvement of microorganism in global cycling of arsenic is well-known. Arsenite-oxidizing bacteria play an important role in reducing arsenic toxicity and mobility in arsenic contaminated environment. In this study, a gram negative bacterium, MM-7 able to efficiently oxidize arsenite [As (III)] to arsenate [As (V)] was isolated from soil. The 16S rRNA analysis revealed that the strain is a close relative to Stenotrophomonas panacihumi with 99% identity. The presence of the arsenite oxidase gene was detected in this bacterium. The amino acid sequences of the arsenite oxidase from MM-7 showed the highest identity with the arsenite oxidase from Bosea sp. (67%). To our knowledge, this is the first report of As (III) oxidation by Stenotrophomonas sp. This strain has great potential for remediation of arsenic contaminated water. © 2012 Taylor & Francis Group.

Arsenic contamination of groundwater and surface water is widespread throughout the world. Due to its carcinogenicity and toxicity to human and animal health, remediation of arsenic contaminated water has become a high priority. There are several physico-chemical based conventional technologies available for arsenic removal from water. However, these technologies have some limitations such as high cost, generation of toxic by-products etc. Therefore, research on sustainable and cost-effective arsenic removal technologies for water has gained enormous attention recently. This paper will focus on the state-of-art knowledge on the currently available arsenic remediation methods, their prospects and recent advances with particular emphasis on bioremediation approaches. © 2012 Taylor & Francis Group.