Characterization of arsenite-oxidizing bacteria isolated from arsenic-contaminated groundwater of West Bengal

Nine arsenic (As)-resistant bacterial strains isolated from As-rich groundwater samples of West Bengal were characterized to elucidate their potential in geomicrobial transformation and bioremediation aspects. The 16S rRNA gene-based phylogenetic analysis revealed that the strains were affiliated with genera Actinobacteria, Microbacterium, Pseudomonas and Rhizobium. The strains exhibited high resistance to As [Minimum inhibitory concentration (MIC) >= 10 mM As3+ and MIC >= 450 mM As5+] and other heavy metals, e. g., Cu2+, Cr2+, Ni2+, etc. (MIC >= 2 mM) as well as As transformation (As3+ oxidation and As5+ reduction) capabilities. Their ability to utilize diverse carbon source(s) including hydrocarbons and different alternative electron acceptor(s) (As5+, SO42, S2O32, etc.) during anaerobic growth was noted. Growth at wide range of pH, temperature and salinity, production of siderophore and biofilm were observed. Together with these, growth pattern and transformation kinetics indicated a high As3+ oxidation activity of the isolates Rhizobium sp. CAS934i, Microbacterium sp. CAS905i and Pseudomonas sp. CAS912i. A positive relation between high As3+ resistance and As3+ oxidation and the supportive role of As3+ in bacterial growth was noted. The results highlighted As3+ oxidation process and metabolic repertory of strains indigenous to contaminated groundwater and indicates their potential in As3+ detoxification. Thus, such metabolically well equipped bacterial strains with highest As3+ oxidation activities may be used for bioremediation of As contaminated water and effluents in the near future.