Isolation and identification of arsenic resistant bacteria: a tool for bioremediation of arsenic toxicity

The soil and groundwater of Asanpara village (Bhagobangola I block) of Murshidabad district are contaminated with non-permissible limit of arsenic and other elements that co-exist with arsenic in various chemical compounds like arsenopyrite, ferrous arsenate, ferric arsenate, etc. Arsenic resistant bacteria (ARB) were isolated from arsenic contaminated soil of Asanpara and biochemically characterized. These bacteria were identified as Lysinibacillus sp. and Bacillus safensis by 16S rDNA sequencing and subsequent phylogenetic analysis. Isolated strains could grow in 76.98 mM and 88.53 mM of arsenite, and 560.88 mM and 721.13 mM of arsenate, respectively. ARB also show hypertolerance to other toxic metals like copper (Cu2+), cobalt (Co2+) and chromium (Cr3+). The level of arsenic and other heavy metal tolerance is unprecedented. Based on the inhibition of urease activity of isolated ARB by cadmium, the bacteria can be used to detect the presence of cadmium. These bacteria could biotransform arsenite into arsenate, which explains its uninhibited growth at very high arsenic concentration. The change in size of these bacteria depicted by scanning electron microscopy is a defence mechanism against arsenic stress Lysinibacillus sp. shows 32.33%, 31.29% and 31.20% bioremediation, whereas Bacillus safensis shows 37.54%, 35.26% and 35.24% bioremediation in the presence of 0.027 mM (2 ppm), 0.133 mM (10 ppm) and 0.667 mM (50 ppm) arsenic, respectively. Also, these bacteria could bioaccumulate or bioadsorb arsenic. The bioremediation potential of isolated ARB could be exploited for removal of arsenic from soil, groundwater and wastewater.