Enzymatic Chromium (VI) Reduction by Cytoplasmic and Cell Membrane Fractions of Chromate-Reducing Bacterium Isolated From Sewage Treatment Plant

Hexavalent chromium is a toxic heavy metal in environment. To remove it from the system, reduction to the trivalent form using microorganisms is an alternative cost-effective method compared to the conventional physicochemical methods. Bacillus cereus Pf-1was isolated and tested for the reduction potential of Cr (VI) using different sub-cellular fractions. Diphenylcarbazide method was used to measure the remaining Cr (VI) concentration in supernatant after centrifugation, and the pellet was used for Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analysis. Almost complete reduction of Cr (VI) was reported for initial Cr (VI) concentration from 10-50 mg/L. Assay with permeabilized cells (treated with Toluene and Triton X-100) and cells free assay demonstrated that Cr (VI) reduction activity was mainly associated with the cytoplasmic fraction of the cells. Considering the major amount of Cr (VI) being reduced within 24 h, the chromate reductase could have been released during growth. Additionally, SEM analysis showed that Bacillus cereus treated with Cr (VI) grew well and had uniform size. EDX analysis revealed certain amounts of chromium in cells treated with Cr (VI). Based on this, Bacillus cereus Pf-1 could be considered as a potential reducing agent for Cr (VI) in aqueous solutions.