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15 <br />catalyze the oxidation of elemental sulfur and S203 <br />species to SO4 It doesn't appear to attack Sz or S_. <br />Ferrobacillus microorganisms were previously known (24, <br />26), but recently it was concluded that they were the <br />same as Thiobacillus ferrooxidans. These bacteria work <br />at pHs between 2 and 3.5. <br />B. Thiobacillus thiooxidans: Gains its primary nourishment <br />by catalyzing the reaction of all sulfur species S2=,- S , <br />S0, 5203 to SO4 It is uncertain whether it can cata- <br />lyze Fe(II) to Fe(III). The organism can catalyze the <br />oxidation of sulfide minerals such as CuS and ZnS. It <br />functions best at pH's between 3.5 and 2.0. <br />There has been much discussion concerning which species <br />• actually catalyzes pyrite oxidation. Dugan (24) has recently <br />found that neither T ferrooxidans nor T thiooxidans alone <br />is effective in the attack on pyrite in coal and that mixed <br />cultures worked the best. Probably both species are present <br />in severe mine drainage situations. There is also much <br />discussion over whether other species are catalyzing reactions <br />above a pH of 3.5 (8, 26). It appears that other bacteria <br />are really effective only in special situations and that <br />the above two species are most important in mine drainage <br />situations (6, 8, 23). It has been shown that these organisms <br />increase the rate of pyrite oxidation by over a thousand <br />times the abiotic rate (6, 8, 23). Once Fe(III), S04 and H+ <br />are released, these species are also powerful catalysts for <br />the weathering of other sulfide minerals (11).