Membrane-associated hexavalent chromium reductase of Bacillus megaterium TKW3 with induced expression

Abstract

Hexavalent chromium (Cr6+) is a highly harmful pollutant, which can be detoxified and precipitated through reduction to Cr3+. Bacillus megaterium TKW3 previously isolated from chromium-contaminated marine sediments was capable of reducing Cr6+ in concomitance with metalloids (Se4+, Se6+, and As5+). Notwithstanding approximately 50% inhibition, it was the first report of simultaneous bacterial reduction of Cr6+ and Se4+ (to elemental Se). No significant difference was observed among electron donors (glucose, maltose, and mannitol) on Cr6+ reduction by B. megaterium TKW3. The reduction was constitutive and determined to be non-plasmid mediated. Peptide mass fingerprints (PMF) revealed a novel aerobic membrane-associated reductase with Cr6+-induced expression and specific reductive activity (in nmol Cr6+/mg protein/min) of 0.220 as compared with 0.087 of the soluble protein fraction. Respiratory inhibitor NaN3 did not interfere with the reductase activity. Transmission electron microscopy with energy dispersive X-ray (TEM-EDX) analysis confirmed the aggregation of reduced chromium along the intracellular membrane region. Future identification of the N-terminal amino acid sequence of this reductase will facilitate purification and understanding of its enzymatic action. © The Korean Society for Microbiology and Biotechnology.