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A Bacillus strain TCL isolated from Jharia coalmine with remarkable stress responses, chromium reduction capability and bioremediation potential

Sohini Banerjee, Arijit Misra, Shibani Chaudhury, Bomba Dam
Journal of hazardous materials 2019 v.367 pp. 215-223
Bacillus cereus, EDTA (chelating agent), bioremediation, cadmium, chromium, copper, cytoplasm, enzyme activity, exopolysaccharides, inoculum, lakes, lead, leather industry, metabolic inhibitors, nickel, nitrites, nucleotide sequences, nutrient content, oxyanions, pH, phenol, ribosomal RNA, sequence homology, sodium azide, stress response, sulfates, temperature, toxicity, transporters, India
Microbial reduction of Cr(VI) to Cr(III) can mitigate environmental chromium toxicity. A chromium, cadmium and nickel tolerating strain TCL with 97% 16S rRNA gene sequence homology to Bacillus cereus was isolated from a derelict open-cast, Tasra Coalmine Lake of Jharia, India. It could tolerate up to Cr2000 [2,000 mg L−1 Cr(VI)] and completely reduce Cr200 within 16 h under heterotrophic condition. TCL grown in ≥ Cr500 exhibited multifarious stress responses particularly in its prolonged lag-phase, like cell aggregation, up to two-fold elongation, increased exopolysaccharide production, and stress enzyme activities. These were relieved by increasing inoculum size or nutrient content. Chromium reduction was constitutive, with maximum activities detected in loosely-bound exopolysaccharides and membrane fractions, followed by cytoplasm and spent media. Cr(VI) was efficiently reduced to Cr(III) and >90% was released in spent media. Cells also expressed Cr-induced active efflux pumps. Growing cells or its crude enzyme extracts could efficiently reduce Cr(VI) in diverse temperatures (15–45 °C), pH (5–9); and in presence of other metals (Cd, Cu, Mo, Ni, Pb), oxyanions (SO4−2, NO2−), and metabolic inhibitors (phenol, NaN3, EDTA). Growth and reduction were also detected in nutrient-limited minimal salt media, and contaminated leather industry effluent thereby making TCL a potential candidate for bioremediation.