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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 performed 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 sample that contained chalcopyrite and covellite. We found that 0.5 g/L of As does not affect living biomass or biooxidative activity on Cu sulfides, but it dissolves Cu, while As precipitates as arsenic acid (H 3 AsO 4 ·½H 2 O). The arsenic tolerant community, as identified by 16S rDNA gene sequence analysis, was composed of three main metabolic groups: chemolithotrophs ( Leptospirillum ,  Sulfobacillus ); chemolithoheterotrophs and organoheterotrophs as  Acidovorax temperans ,  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 H 3 AsO 4 -As(V) detoxification and strengthens the community’s response to As.

Community of thermoacidophilic and arsenic resistant microorganisms isolated from a deep profile of mine heaps