Ferrous Iron and Pyrite Oxidation by “Acidithiomicrobium” Species

Novel iron- and sulfur-oxidizing, moderate thermophiles were isolated from an acidic geothermal site and from a previously studied, pyrite-enrichment mixed culture (which also contained the related actinobacterium Acidimicrobium ferrooxidans). The novel species (proposed genus “Acidithiomicrobium”) grew autotrophically with ferrous iron at an optimum temperature of about 50°C, efficiently degraded pyrite at 55°C and also grew well autotrophically on sulfur. The extensive dissolution of pyrite during autotrophic growth contrasted with a requirement for yeast extract for significant growth of the related Acidimicrobium ferrooxidans.