Isolation, characterization, and multiple heavy metal-resistant and hexavalent chromium-reducing Microbacterium testaceum B-HS2 from tannery effluent

A Cr6+ resistant Microbacterium testaceum B-HS2, isolated indigenously from tannery wastewater, showed optimum growth at 37 degrees C and pH 7. M. testaceum B-HS2 could resist to Cr6+ (48 mM) and heavy metals upto 2 mM (As2+, Zn2+, Cu2+), 7 mM (Pb2+) and 1 mM (Cd2+, Ni2+). Maximum activity of chromate reductase was achieved at 40 degrees C at pH of 7 and was inhibited in presence of all the heavy metals tested. M. testaceum B-HS2 biosorption efficiency (q) for Cr6+ was 31, 38, 66 and 47 mM/g after 2, 4, 6 and 8 days, respectively. Electron micrographs confirmed further the adsorption of metal leading to intracellular accumulation of Cr6+. Functional groups such as amide and carbonyl moieties which actively participated in Cr6+ adsorption were determined through FTIR spectroscopy, and intracellular accumulation was also confirmed by energy dispersive X-ray (EDX) and scanning electron microscopy (SEM) analysis. Cr6+ presence triggers significant production of antioxidant enzymes [(Ascorbate peroxidase (APOX), Superoxide dismutase (SOD), Peroxidase (POX), Glutathione S-transferease (GST), and Catalase (CAT)]. Moreover, rise in glutathione and other non-protein thiol levels were determined which substantially neutralize Cr6+ generated oxidative stress. Pilot scale study revealed that M. testaceum B-HS2 was helpful in removing up to 96% Cr6+ from tannery effluent within 6 days and this microbial purified water is safe for the plant growth. Multiple heavy metal tolerance and high Cr6+ reduction potential make M. testaceum B-HS2 a candidate of choice to reclaim Cr6+ contaminated environment. (C) 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University.