Moderate thermophiles including “Ferroplasma cupricumulans” sp. nov. dominate an industrial-scale chalcocite heap bioleaching operation

This study describes the microbiology of the MICCL Monywa chalcocite heap bioleaching operation. Microorganisms were detected in the heap using culture-based techniques and culture-independent PCR–DGGE analysis of the 16S rRNA gene. The metabolic requirements, temperature and pH optima were determined for selected strains isolated from the heap material.Six strains (BH1–BH6) were enriched and isolated from heap solids and leachate samples. Phylogenetic analysis of the 16S rRNA genes showed that strains BH3 and BH4 were closely related to the acidophilic bacterium Acidithiobacillus caldus and strains BH5 and BH6 were closely related to Leptospirillum ferriphilum. The optimum growth temperature for one of the L. ferriphilum strains was 41.3 °C and the optimum pH range was 1.1 to 1.5.A new species of Archaea was isolated from the heap samples. Cells of the proposed species, “Ferroplasma cupricumulans” (formerly “Ferroplasma cyprexacervatum”), were non-motile pleomorphic cocci, capable of chemomixotrophic growth with ferrous sulphate and yeast extract. Cells grew anaerobically on potassium tetrathionate and yeast extract as electron donors with ferric iron as the electron acceptor. Growth occurred from 22 °C to 63 °C, with an optimum temperature of 53.6 °C. The optimal pH for growth was 1.0–1.2. Phylogenetic analysis based on the 16S rRNA gene showed the most closely related described species to strain BH2 was Ferroplasma acidiphilum YT (95% sequence similarity).Molecular analysis of mine samples (16S rRNA PCR–DGGE) detected the above-mentioned cultured strains as well as species of Sulfobacillus and unknown representatives of the Proteobacteria.The microbial community of the Myanmar bioleach heaps contained similar levels of diversity to a dump bioleach operation in Chile, but contained greater amounts of biomass than another heap bioleach operation in Australia. The operating parameters of the Myanmar heaps have selected for the growth of moderately thermophilic microorganisms that are more commonly found in extremely low pH acidic mine drainage sites than in heap bioleach systems. The novel species of Ferroplasma is considered to be involved in the aerobic and anaerobic cycling of iron within the heap bioleaching environment.