DISTRIBUTION OF THIOBACILLUS-FERROOXIDANS AND LEPTOSPIRILLUM FERROOXIDANS - IMPLICATIONS FOR GENERATION OF ACID-MINE DRAINAGE

Although Thiobacillus ferrooxidans and Leptospirillum ferrooxidans are widely considered to be the microorganisms that control the rate of g eneration of acid mine drainage, little is known about their natural d istribution and abundance. Fluorescence in situ hybridization studies showed that at Iron Mountain, California, T. ferrooxidans occurs in pe ripheral slime-based communities (at pH over 1.3 and temperature under 30 degrees C) but not in important subsurface acid-forming environmen ts (pH 0.3 to 0.7, temperature 30 degrees to 50 degrees C). Leptospiri llum ferrooxidans is abundant in slimes and as a planktonic organism i n environments with lower pH. Thiobacillus ferrooxidans affects the pr ecipitation of ferric iron solids but plays a limited role in acid gen eration, and neither species controls direct catalysis at low pH at th is site.