Microbial responses to environmental arsenic

Abstract

Microorganisms have evolved dynamic mechanisms for facing the toxicity of arsenic in the environment. In this sense, arsenic speciation and mobility is also affected by the microbial metabolism that participates in the biogeochemical cycle of the element. The ars operon constitutes the most ubiquitous and important scheme of arsenic tolerance in bacteria. This system mediates the extrusion of arsenite out of the cells. There are also other microbial activities that alter the chemical characteristics of arsenic: some strains are able to oxidize arsenite or reduce arsenate as part of their respiratory processes. These type of microorganisms require membrane associated proteins that transfer electrons from or to arsenic (AoxAB and ArrAB, respectively). Other enzymatic transformations, such as methylation-demethylation reactions, exchange inorganic arsenic into organic forms contributing to its complex environmental turnover. This short review highlights recent studies in ecology, biochemistry and molecular biology of these processes in bacteria, and also provides some examples of genetic engineering for enhanced arsenic accumulation based on phytochelatins or metallothionein-like proteins.

Efflux Permease CgAcr3-1 of Corynebacterium glutamicum Is an Arsenite-specific Antiporter

“…Two of them, Cgacr3-1 and Cgacr3-2, encode active arsenite efflux proteins, whereas Cgacr3-3 does not seem to be functional. The presence of several gene copies for bacterial As(III) detoxification is not an infrequent occurrence (31). It allows organisms, such as the saprophytic C. glutamicum, to respond to high concentrations of environmental As(III).…”

Arsenic methylation by an arsenite S-adenosylmethionine methyltransferase from Spirulina platensis

“…The mechanisms of As biotransformation including oxidation, reduction, and methylation have been widely studied. Arsenite (As(III)) oxidation is believed to be a detoxification pathway since arsenate (As(V)) is less toxic than As(III) (Armendariz et al, 2015;Paez-Espino et al, 2009). Although the possible intermediate products methylarsenite (MMA(III)) and dimethylarsenite (DMA(III)) are more toxic, As methylation is acknowledged as a pathway of detoxification in microbes Wang et al, 2014b).…”

Arsenic modulates the composition of anode-respiring bacterial community during dry-wet cycles in paddy soils

“…Deltaproteobacteria was also found to be dominant in arsenic removal water treatment system (Upadhyaya et al 2012). Several mechanisms have been proposed for As detoxification in microbes: As(V) reduction, methylation, and excretion, which are widely found in anaerobic bacteria (Zhu et al 2014;Oremland and Stolz 2003;Paez-Espino et al 2009). The anaerobic bacteria are proposed to adopt the ancient high As environment and evolve the anaerobic arsenate respiration (Zhu et al 2014).…”