Kinetic Studies of Iron Oxidation by Whole Cells of Ferrobacillus ferrooxidans

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Abstract
A colorimetric assay was developed for studying the kinetics of iron oxidation with whole cells of the chemoautotroph, Ferrobacillus ferrooxidans. The assay was more advantageous than the conventional method of Warburg manometry because of its simplicity, rapidity, and the small amount of cells required. The assay measured Fe3+ as a chloride complex which absorbs at 410 nm. Kinetic analysis showed the apparent Km for iron oxidation to be 5.4 × 10−3m in an unbuffered system and 2.2 × 10−3m in the presence of β-alanine-SO42− buffer. Glycine and β-alanine buffers were used in the measurement of the pH optimum for iron oxidation; the optimum ranged from 2.5 to 3.8. The effect of pH was primarily on the Vmax while the Km remained constant. Added SO42− was found to stimulate iron oxidation by increasing the Vmax of iron oxidation by whole cells, but it did not affect the Km. Results of assays of iron oxidation in systems containing various mole percentages of SO42− and Cl− indicated that Cl− did not inhibit iron oxidation but that SO42− was required. Sulfate could be partially replaced by HPO42− and HAsO42− but not by BO3−, MoO42−, NO3−, or Cl−; formate and MoO42− inhibited iron oxidation.