Evaluation of bacterial strains isolated from Late Quaternary alluvial sediments spanning ~ 28 m in depth for heavy metal tolerance and Cr(VI) removal ability.

Microbial heavy metal tolerance in subsurface samples is indicative of long-term ecotoxicological impact of metals and could also reflect metal contamination of groundwater. However, the heavy metal tolerance characteristics of microbes isolated from subsurface river sediment profiles are still obscure. In the present study, determination of heavy metal tolerance of bacterial strains isolated from two Late Quaternary sediment profiles (~ 28 m and ~25 m deep) located at the Mahi river basin, Western India, was carried out. Identification of bacterial isolates by the 16S rRNA gene sequencing revealed that bacterial isolates affiliated with phyla Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidetes were dominant in both sediment profiles. Heavy metal tolerance of bacterial strains as determined by plate diffusion assay revealed order of metal tolerance as follows: Hg(II)<Cd(II)< Ni(II)<Cu(II)=Cr(VI). Chromate removal study in liquid medium suggested that bacterial strains procured from subsurface possessed the ability to remove Cr(VI) with varied magnitude. A packed bed column experiment indicated that bacterial strains obtained from the subsurface have the potential for Cr(VI) removal from different particle size consistencies of the sediments.