Tolerance to arsenic in the environmental isolate Terribacillus sp. AE2B 122

Terribacillus sp. AE2B 122 is an environmental strain isolated from olive-oil agroindustry wastes. This strain displays resistance to different metals, including arsenic. This strain possesses an unusual ars gene organization cluster. The expression of this operon was induced when cells were exposed to sub-lethal concentrations of arsenate. Heterologous expression of the two Te3676 and Te 3675 genes in Escherichia coli ∆arsRBC mutant strains and accumulation assays in these strains and Terribacillus sp. AE2B 122 demonstrated that Te3676, a transcriptional repressor, and Te 3675, an arsenite efflux pump, are associated with the arsenic tolerance in this environmental strain. Moreover, two scattered arsC-like genes (Te3384 and Te2854) were detected in the genome. However, these two arsC-like genes do not appear to act as reductases in the arsenic resistance in Terribacillus sp. AE2B 122, although these two genes seem to contribute to the resistance using an unravel mechanism. Moreover, this bacterium does not accumulate As(V) suggesting that an exclusion mechanism, as well as an extrusion mechanism are responsible for arsenate resistance. However, even though the reduction of As(V) to As(III) is described as an usual step in most resistance mechanisms of bacteria to this metal, we do not found evidence for this reduction in Terribacillus sp. AE2B.