Seven Fe2+-oxidising acidophilic bacterial strains were isolated at 50 degreesC from a pyritic coal from Collie, Australia and from a Fe2+-oxidising fluidised bed reactor running at 60 degreesC which was originally inoculated with the Collie coal. The 16S rRNA gene of five of the strains was partially sequenced. The strains isolated from the reactor were closely related (99% similarity in gene sequence) to Sutfobacillus thermosulfidooxidans and the strains isolated directly from the coal had a 97% gene sequence similarity to "Sulrobacillus yellowstonensis". The sequenced strains each hail an optimum temperature for growth using an organic carbon source of approximately 50 degreesC and a maximum temperature for growth of approximately 60 degreesC. All strains required a mixotrophic medium for growth on Fe 21 or on an organic carbon source. Of the five strains tested, all grew on pyrite whereas only three of the strains grew on chalcopyrite. The "S. yellowstonensis" -like strains grew better on S' than the other strains. The S. thermosulfidooxidans -like strains were more tolerant then the other strains to Cu2+ and Cl-. The "S. yellowstonensis" -like strains contained omega-cycloheptyl-18:0 and omega-cycloheptyl-18:0 2OH phospholipid fatty acids, whereas the S. thermosulfidooxidans-like strains contained no omega-cyclofatty acids in the phospholipid fraction. These strains have potential to be used in the bioleaching of heaps, especially the S. thermosulfidooxidans-like strains. Work is continuing to further characterise their bioleaching abilities and their usefulness in a commercial heap leach environment. (C) 2002 Elsevier Science Ltd. All rights reserved.