Ramírez-Díaz MI, Riveros-Rosas H, Campos-García J, Cervantes C

Language: Spanish
References: 16
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ABSTRACT

Bacterial reduction of hexavalent chromium: mechanisms and applications.
The broad industrial use of derivatives of chromium, a heavy metal, has caused that these compounds are regarded as serious environmental contaminants. In nature, chromium is found primarily in two oxidation states: the trivalent form Cr (III), which is relatively innocuous, and the hexavalent formCr (VI), considered a more toxic species. At the extracellular level, Cr (III) is relatively harmless because of its insolubility. In contrast, inside the cell Cr (III) is highly toxic because of its ability to bind to DNA and proteins. Cr (VI) is usually found as chromate (CrO₄ ^2-) or dichromate (Cr₂O₇ ^2-) ions, which easily cross the plasmatic membrane to be mistakenly taken up arrested by the sulfate transport systems. In the environment, Cr (VI) can be reduced to Cr (III), either by abiotic ways or by enzymes called chromate reductases. The study of these enzymes has gained great interest for their potential use in bioremediation of pollution by chromate. Several chromate reductases have been identified in different bacterial species. The best characterized chromate reductase is the ChrR enzyme from the gram-negative bacteria Pseudomonas putida, which belongs to the family of NAD(P)H dependent flavoprotein reductases. This family currently includes 243 ChrR homologous proteins that bind the FMN cofactor and that are widely distributed in the three domains of life. This paper summarizes the properties of bacterial systems that reduce Cr (VI) as a mechanism used by microorganisms to resist the toxic effects of chromiumand its derivatives.

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