Abstract

Several species that conserve energy from ferrous iron and sulfur oxidation are included in the Acidithiobacillus genus. The recognized differences between those species are tolerance to low temperature, low pH, chloride, transition metals and aluminum. Two different sequences from the Acidithiobacillus genus closed related to At. ferrooxidans were retrieved from the very beginning of the industrial process at Escondida mine (2001-2002), and representative isolates were obtained and identified as strains D2 and DM. Furthermore, two new species, At. ferriphilus and At. ferrivorans, were reported, which match 100% with those sequences, respectively, by 16S rRNA gene comparison. The reported percentage of similarity between both type strains 16S sequences is 89% and the ANI calculation based on MUMmer reported between At. ferriphilus and At. ferrivorans is 93.4%. Each of those isolates were grown in the lab at different conditions, and quantitative polymerase chain reaction (Q-PCR) was used to monitor their population in the industrial bioleaching heap during 16 years of operation. The duplication time of D2 was lower with ferrous iron and sulfur than that of DM, but was higher than that of DM when growing anaerobically with the oxidation of reduced elemental sulfur coupled to ferric iron reduction. The abundance of D2 and DM were similar at the initial stage of the industrial process when one lift of the heap was on irrigation, varying during the leaching cycle of each strip. In the actual stage of the industrial heap, with six lifts in operation, the abundance of DM was higher than that of D2 during the whole leaching cycle. We will describe the historical development of both strains in the industrial heap and the behavior of several parameters that have changed in that time, such as the acid content in the irrigation solution, the concentration of sulfate and aluminum as impurities, and the temperature.