Optimization and characterization of chromium(VI) reduction in saline condition by moderately halophilic Vigribacillus sp isolated from mangrove soil of Bhitarkanika, India

A Gram-positive moderately halophilic Cr(VI) tolerant bacterial strain H4, isolated from saline mangrove soil, was identified as Vigribacillus sp. by biochemical characterization and 16S rRNA analysis. In LB medium, the strain could tolerate up to 1000 mg L−1 Cr(VI) concentra-tion and reduced 90.2 and 99.2% of 100 mg L−1 Cr(VI) under optimized set of condition within 70 h in absence and presence of 6 wt.% NaCl, respectively. The fitting of time course reduction data to an exponential rate equation yielded the Cr(VI) reduction rate constants in the range (0.69–5.56) × 10−2 h−1. Analyses of total chromium and bacterial cell associated with reduced product by AAS, SEM/EDS, TEM/SAED, FT-IR and UV–vis–DRS indicated the formation of about 35% of insoluble Cr(III) either as Cr(OH)3 precipitate in nanometric size or immobilized on the bacterial cell surface while the remaining 65% of reduced chromium was present as soluble Cr(III) in the growth medium. Powder XRD analysis revealed the amorphous nature of the precipitated Cr(OH)3. The high Cr(VI) reducing ability of the strain under saline condition suggests the Vigribacillus sp. as a new and efficient strain capable of remediating highly saline Cr(VI) polluted industrial effluent