Insights into the characterization of ars genes in the biomining bacterium Acidithiobacillus caldus SM-1

Acidithiobacillus caldus is an extremely acidophilic, moderately thermophilic, chemoautotrophic bacterium, which has been used to treat gold-bearing arsenopyrite ores. The arsenic resistance system (ars operon) was responsible for arsenic resistance of A. caldus. To investigate the characterization of ars genes, we analyzed 12 ars genes in A. caldus SM-1 using the bioinformatics database and softwares. Their amino acid composition and physical and chemical characteristics were predicted. Secondary structure simulations revealed that the dominant patterns were predicted to be alpha helix and random coil among the 12 ars proteins. Three-dimensional structure analysis showed that there totally existed three major types of three-dimensional structure of the 12 ars proteins in A. caldus SM-1. Subcellular localization of these proteins indicated that these ars proteins were mainly located in the bacterial cytoplasm, while Atc_0977, Atc_1809 and Atc_m110 were especially localized in bacterial inner membrane. Furthermore, DNA-binding residues in ArsR proteins and binding sites of ArsC-As were predicted. Phylogeny analysis revealed that A. caldus, A. ferrooxidans, A. ferrivorans and A. thiooxidans were well-supported group based on ArsB and ArsC sequences data. This bioinformatics analysis of ars genes could help in probing to the arsenic resistance of A. caldus SM-1.