Effect of mineral nutrients and organic substances on the development of Thiobacillus ferrooxidans

The effect of inorganic nutrients on iron oxidation by Thiobacillus ferrooxidans was studied using a concentration of 2.0 g Fe2+/liter. Besides ammonium-nitrogen and phosphorus, the essential nutrients were sulphate and magnesium, with the lowest unlimiting concentration being 2.0 g SO/liter and 2.0 mg Mg2+/liter for a suspension of about 108 cells/ml. Omitting nitrate, calcium, potassium, and chloride had no influence on the iron oxidation. Nitrate and chloride were inhibitory in high concentrations although the bacteria were able to adapt to their presence. Several organic compounds tested in 0.5% (w/v) concentrations inhibited iron oxidation. Complete inhibition up to 14 days was caused by fructose, lactose, meat extract, yeast, extract, peptone, and tryptone. T. ferrooxidans-strains were able to adapt to the presence of organic material even though they were not necessarily able to use the organic compounds for energy. Some general conclusions are made concerning the role of nutrients in leaching processes.