Isolation and characterization of a highly effective bacterium b-525k for hexavalent chromium detoxification.

The chromate resistant Gram-positive strain b-525k was isolated from tannery effluents, demonstrating optimal propagation at 37 °C and pH 8. The minimum inhibitory concentration (MIC) test showed that b-525k can tolerate up to 32 mM Cr, and also exhibit the ability to resist other toxic metal ions including Pb (23 mM), As (21 mM), Zn (17 mM), Cd (5 mM), Cu (2 mM), and Ni (3 mM) with the resistance order as Cr > Pb > As >Zn >Cd >Ni >Cu. b-525k showed maximum biosorption efficiency () of 51 mM Cr/g after 6 days. Chromate stress elicited pronounced production of antioxidant enzymes such as catalase (CAT) 191%, glutathione transferase (GST) 192%, superoxide dismutase (SOD) 161%, peroxidase (POX) 199%, and ascorbate peroxidase (APOX) (154%). Within b-525k, the influence of Cr stress (2 mM) did stimulate rise in levels of GSH (907%) and non-protein thiols (541%) was measured as compared to the control (without any Cr stress) which markedly nullifies Cr generated oxidative stress. The pilot scale experiments utilizing original tannery effluent showed that b-525k could remove 99% Cr in 6 days, thus, it could be a potential candidate to reclaim the chromate contaminated sites.