[Bacterial resistance to arsenic compounds].

Arsenic compounds, often present as environmental pollutants, are highly toxic for most microorganisms. Some microbial strains possess genetic determinants conferring resistance to arsenic derivatives. In bacteria, these determinants are usually located on plasmids, which has facilitated their analysis with molecular detail. Bacterial plasmids conferring arsenic resistance encode specific pumps that extrude arsenite (AsIII). In Gram-negative bacteria, the efflux pump consists of a complex formed by an ATPase (ArsA) associated with a membrane anion channel (ArsB). Arsenate (AsV) is converted to arsenite by a soluble reductase (ArsC). Proteins ArsB and ArsC, but not the ATPase, are also found in Gram-positive bacteria. Besides the widely spread plasmid arsenic resistance determinants, some bacteria possess the ability to enzimatically oxidize arsenite to less toxic arsenate.