Bioreduction of Cr(VI) to Cr(III) by reducing microbes has attracted increasing concern. Here, Cr(VI) removal capacity of a Cr(VI)-resistant bacterium isolated from activated sludge was investigated. Based on its physio-biochemical attributes and 16S rDNA sequence analysis, the strain was identified as Bacillus cereus ZY-2009. It grew normally in the media containing 10-100 mg/L Cr(VI), indicating its high resistance to Cr(VI). Under the optimal conditions of pH 7.0, inoculation amount 10%, and temperature 30°C, Cr(VI) was effectively removed, with a removal rate of ∼80%. Co-existing Fe3+ and Cu2+ greatly increased Cr(VI) removal, but Cd2+ showed significant inhibition. Cr(VI) was removed mainly via enzyme-mediated bioreduction but not biosorption. Cr(VI) was reduced by different cell fractions (i.e. extracellular secretions, cytoplasm, and cell envelope), implying that Cr(VI) can be reduced both extracellularly and intracellularly. This strain can be used in the bioremediation of Cr(VI)-containing wastewater, with Fe3+ and Cu2+ as stimulators.
Keywords: Bacillus cereus; Cr(VI)-reducing bacteria; Hexavalent chromium; bioreduction; bioremediation.