Isolation and characterization of arsenate reducing proteobacterium

Arsenic (As) is a known carcinogen and occurs in the environment as arsenate As(V) and arsenite As(III). Arsenite is more toxic and more mobile than arsenate. Microbial As redox transformations are important drivers controlling As speciation in soils, sediments and waters. As(III) oxidation and As(V) reduction are strategies for either detoxification or for generating energy. Among the bacterial mechanisms to avoid the toxicity of arsenic are: (i) minimizing the uptake of arsenate through the system for phosphate uptake (Cervantes et al., 1994), (ii) peroxidation reactions with the membrane lipids (Abdrashitova et al., 1986), (iii) using the arsenic detoxification pathway involving the ars operon (Silver and Phung, 1996). Bacterial ars systems confer arsenic resistance primarily by encoding a specific efflux pump, the product of the arsB gene that extrudes As(III) from the cytoplasm and thus lowers the intracellular concentration of arsenic. Prior to efflux, arsenate is enzimatically reduced to arsenite by the cytoplasmatic arsenate reductase, the product of the arsC gene (Silver et al., 2001). The present work reports the initial identification and characterization of an as resistant proteobacterium capable of reducing as(v) under aerobic condition.