Bacterial mechanisms for Cr(VI) resistance and reduction: an overview and recent advances.
Chromium pollution is increasing incessantly due to continuing industrialization. Of various oxidation states, Cr(6+) is very toxic due to its carcinogenic and mutagenic nature. It also has deleterious effects on different microorganisms as well as on plants. Many species of bacteria thriving in the Cr(6+)-contaminated environments have evolved novel strategies to cope with Cr(6+) toxicity. Generally, decreased uptake or exclusion of Cr(6+) compounds through the membranes, biosorption, and the upregulation of genes associated with oxidative stress response are some of the resistance mechanisms in bacterial cells to overcome the Cr(6+) stress. In addition, bacterial Cr(6+) reduction into Cr(3+) is also a mechanism of specific significance as it transforms toxic and mobile chromium derivatives into reduced species which are innocuous and immobile. Ecologically, the bacterial trait of reductive immobilization of Cr(6+) derivatives is of great advantage in bioremediation. The present review is an effort to underline the bacterial resistance and reducing mechanisms to Cr(6+) compounds with recent development in order to garner a broad perspective.
Department of Agricultural Microbiology, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh, 202002, U.P., India, muneesmicro@rediffmail.com.
Munees
M
Ahemad
D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002857:Chromium / Q000378:metabolism* / Q000633:toxicity; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology*
D002857:Chromium; C074702:chromium hexavalent ion