Pyrite oxidation and copper sulfide ore leaching by halotolerant, thermotolerant bacteria

Pyrite oxidation was observed in a mixed culture of salt-tolerant, thermotolerant, acidophilic bacteria from warm, acidic, coastal sediments of the island of Milos (Greece). Analysis of 16S rRNA gene sequences cloned from DNA extracted from the mixed culture indicated two species which were related to Thiobacillus prosperus. One of the sequences was found previously in warm, sediment samples from the island of Vulcano (Italy). Iron solubilization from pyrite by the Milos culture at 47 °C was most rapid in the presence of NaCl at 30 g l−1. A novel species was isolated from the mixed culture and grew in pure culture on pyrite with 50 g l−1 NaCl, but iron solubilization was most rapid at just below 50 °C with 20 g l−1 NaCl. Establishment of activity of the halotolerant, thermotolerant bacteria in copper sulfide ore leaching columns was more difficult than with related bacteria growing at lower temperatures.