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

The chromate resistant Gram-positive Bacillus cereus strain b-525k was isolated from tannery effluents, demonstrating optimal propagation at 37 degrees C and pH 8. The minimum inhibitory concentration (MIC) test showed that B. cereus b-525k can tolerate up to 32 mM Cr6+, and also exhibit the ability to resist other toxic metal ions including Pb2+ (23 mM), As3+ (21 mM), Zn2+ (17 mM), Cd2+ (5 mM), Cu2+ (2 mM), and Ni2+ (3 mM) with the resistance order as Cr6+ > Pb2+ > As3+ > Zn2+ > Cd2+ > Ni2+ > Cu2+. B. cereus b-525k showed maximum biosorption efficiency (q) of 51 mMCr(6+)/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. cereus b-525k, the influence of Cr6+ 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 Cr6+ stress) which markedly nullifies Cr6+ generated oxidative stress. The pilot scale experiments utilizing original tannery effluent showed that B. cereus b-525k could remove 99% Cr6+ in 6 days, thus, it could be a potential candidate to reclaim the chromate contaminated sites. (C) 2022 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.

Automated summary

The chromate resistant bacterium Bacillus cereus b-525k isolated from tannery effluents exhibited high tolerance to various toxic metal ions and showed efficient biosorption of chromium. The bacterium also showed significant production of antioxidant enzymes under chromate stress, alleviating oxidative damage. Pilot-scale experiments demonstrated that Bacillus cereus b-525k effectively removed chromium from tannery effluents, suggesting its potential application in chromate-contaminated sites.