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The Bengal-Delta plain at Indo-Bangladesh border is severely affected with groundwater arsenic contamination. The microbial diversity of this site is totally uncharacterized. Here we report the existence of a novel Exiguobacterium strain that could thrive under high arsenic concentrations in the arsenic-infested water of the above region. Drinking water was sampled for presence of bacterial isolates. Analysis of the 16SrRNA sequence of the bacteria isolated revealed them to be members representing various genera. Of particular interest was a new species of genera Exiguobacterium (=MTCC 7757T=JCM 13946T) that thrived in extremely high arsenic concentration, arsenate (30mM) and arsenite (20mM). The growth-rate of the bacterium cultured in arsenate-supplemented medium increased significantly; it gained metabolic energy from arsenate-amended aerobic growth conditions. On analysis of the ars-operon, the strain was positive for arsB, but the genetic contribution to arsenate reduction (arsC) was not recognized, though a differential arsenate reductase activity could be observed. An increased expression of arsB, as an associated process to arsenate reduction, confirmed that arsenic extrusion principle worked behind its survival. Identification of such a bacterium could add to the diversity of bacteria specific to that geographical location and also help us in delineating putative novel arsenic resistance mechanisms operative for survival |
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