Casas‑Flores et al. AMB Expr (2015) 5:54 DOI 10.1186/s13568‑015‑0132‑5 ORIGINAL ARTICLE Community of thermoacidophilic

and arsenic resistant microorganisms isolated from a deep profile of mine heaps S Casas‑Flores1, E Y Gómez‑Rodríguez1 and J V García‑Meza2* Soluble arsenic (As) in acidic feed solution may inhibit the copper (Cu) bioleaching process within mine heaps. To clarify the effect of soluble arsenic on the live biomass and bioxidative activity in heaps, toxicological assays were per‑ formed using a synthetic feed solution given by a mine company. The microorganisms had previously been isolated from two heap samples at up to 66 m depth, and cultured using specific media for chemolithotrophic acidophiles (pH 1–2) and moderate thermophiles (48°C), for arsenic tolerance assay. The four media with the highest biomass were selected to assay As‑resistance; one culture (Q63h) was chosen to assay biooxidative activity, using a heap sam‑ ple that contained chalcopyrite and covellite. We found that 0.5 g/L of As does not affect living biomass or biooxida‑ tive activity on Cu sulfides, but it dissolves Cu, while As precipitates as arsenic acid (H3AsO4·H2O). The arsenic toler‑ ant community, as identified by 16S rDNA gene sequence analysis, was composed of three main metabolic groups: chemolithotrophs (Leptospirillum, Sulfobacillus); chemolithoheterotrophs and organoheterotrophs as Acidovorax tem-perans, Pseudomonas alcaligenes, P. mendocina and Sphingomonas spp. Leptospirillum spp. and S. thermosulfidooxidans were the dominant taxa in the Q63–66 cultures from the deepest sample of the oldest, highest‑temperature heap. The results indicated arsenic resistance in the microbial community, therefore specific primers were used to amplify ars (arsenic resistance system), aio (arsenite oxidase), or arr (arsenate respiratory reduction) genes from total sample DNA. Presence of arsB genes in S. thermosulfidooxidans in the Q63–66 cultures permits H3AsO4‑As(V) detoxification and strengthens the community’s response to As