Research progress in microbial chromium-transformation and resistance and bioremediation

Abstract:

Chromium is a transitional metal mainly existing as hexavalent [CrO42?, Cr2O72?, Cr(VI)] and trivalent [Cr(OH)3, Cr(III)] forms in the natural environment. Several microorganisms have evolved various transformation and resistant mechanisms for chromium detoxification to resist the poisonous chromium. Microbial chromium-transformation contain Cr(VI) reduction and Cr(III) oxidation. Chromate-reducing microbes can transform high toxic Cr(VI) to low or non-toxic Cr(III). These microbes show a big potential to bioremediate chromium-contaminated soil and water. In addition, various microbes have been reported to participate in Cr(III) oxidation. These microorganisms play a key role in the chromium transformation and biogeochemical cycle. So far, four microbial chromium-resistant mechanisms have been found including: (1) reducing the uptake of Cr(VI); (2) Cr(VI) efflux; (3) removing intracellular oxidative stress; and (4) DNA repair. This review mainly focuses on summarizing the molecular mechanisms and new research progress in chromate transformation and bioremediation of chromium contamination by microorganisms.

Key words:Chromium, Chromate, Chromium resistance, Chromate-reducing bacteria, Chromium contamination, Bioremediation