Reduction of chromate by marine bacillus megaterium TKW3

Abstract

Hexavalent chromium (Cr6+) is an important corrosion inhibitor and is also highly toxic pollutant, which can be detoxified and precipitated through reduction to Cr3+. Bacillus megaterium TKW3 isolated from contaminated sediments was capable of reducing Cr6+ in concomitance with metalloids (Se4+, Se6+ and As5+). Notwithstanding the approximately 50% inhibition, it is firstly reported that bacteria reduced Cr6+ and Se4+ [to elemental Se] simultaneously. No significant difference was observed among electron donors (glucose, maltose and mannitol) on Cr6+ reduction of B. megaterium TKW3. The process was mediated by a novel aerobic membrane-associated reductase with Cr6+induced expression, and specific reductive activity of 0.220 nmol (Cr6+) mg-1 (protein) min-1. Respiratory inhibitor NaN3 did not obstruct the reductase activity. Transmission electron microscopy with energy dispersive X-ray analyzer confirmed the aggregation and accumulation of Cr along intracellular membrane region. 2-Dimensional gel electrophoresis analysis of the proteins expressed by B. megaterium TKW3 exposed to Cr6+ vs. that without Cr6+ in culture media revealed positive expression of specific proteins. Further identification of the amino acid sequence of this novel reductase would facilitate understanding of its enzymatic action on Cr6+ reduction and bioremediation. © 2006 by NACE International.