Regulation of Arsenic Metabolic Pathways in Prokaryotes

Abstract

Despite the toxicity of arsenic to most organisms, certain prokaryotes have the ability to grow on arsenic oxyanions by using them as alternative electron acceptors or electron donors. The common forms of arsenic used for these metabolic pathways are arsenate and arsenite. The end result of arsenic-based metabolism is that the organism couples oxidation/reduction of arsenite/arsenate to growth and/or arsenic resistance. Several reviews have been published on the subject of microbial arsenate respiration and oxidation. This chapter presents a summary of the genes and enzymes for arsenate respiration and arsenite oxidation. The chemical differences between arsenate and arsenite manifest different biological responses. In contrast to numerous single-pathway investigations, very few proteomic and transcriptomic approaches have been used for investigating global or systems level changes to the biology of arsenic-metabolizing prokaryote. A variety of microbial ecology studies have been carried out to investigate the abundance, distribution, and expression of ars, arr, and aox genes in a variety of environments. Microbial ecology studies have resulted in an extensive database of arr and aox sequences from a variety of environments. Molecular tools are now available to carry out quantitative aox and arr gene expression studies in environmental samples. These approaches could be used, for example, to determine the occurrence of “hot spots” for biologically mediated arsenate reduction. This could help identify zones in a groundwater environment that are more prone to arsenic mobilization.