Characterization of a thermophilic sulfur oxidizing enrichment culture dominated by a Sulfolobus sp. obtained from an underground hot spring for use in extreme bioleaching conditions.

A thermoacidophilic elemental sulfur and chalcopyrite oxidizing enrichment culture VS2 was obtained from hot spring run-off sediments of an underground mine. It contained only archaeal species, namely a Sulfolobus metallicus-related organism (96% similarity in partial 16S rRNA gene) and Thermoplasma acidophilum (98% similarity in partial 16S rRNA gene). The VS2 culture grew in a temperature range of 35-76 degrees C. Sulfur oxidation by VS2 was optimal at 70 degrees C, with the highest oxidation rate being 99 mg S(0 )l(-1 )day(-1). At 50 degrees C, the highest sulfur oxidation rate was 89 mg l(-1 )day(-1 )(in the presence of 5 g Cl(-) l(-1)). Sulfur oxidation was not significantly affected by 0.02-0.1 g l(-1) yeast extract or saline water (total salinity of 0.6 M) that simulated mine water at field application sites with availability of only saline water. Chloride ions at a concentration above 10 g l(-1) inhibited sulfur oxidation. Both granular and powdered forms of sulfur were bioavailable, but the oxidation rate of granular sulfur was less than 50% of the powdered form. Chalcopyrite concentrate oxidation (1% w/v) by the VS2 resulted in a 90% Cu yield in 30 days.