Kinetic Studies of Iron Oxidation by Whole Cells of Ferrobacillus ferrooxidans

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 Fe 3+ as a chloride complex which absorbs at 410 nm. Kinetic analysis showed the apparent K m for iron oxidation to be 5.4 × 10 −3 m in an unbuffered system and 2.2 × 10 −3 m in the presence of β-alanine-SO 4 2− buffer. Glycine and β-alanine buffers were used in the measurement of the p H optimum for iron oxidation; the optimum ranged from 2.5 to 3.8. The effect of p H was primarily on the V max while the K m remained constant. Added SO 4 2− was found to stimulate iron oxidation by increasing the V max of iron oxidation by whole cells, but it did not affect the K m . Results of assays of iron oxidation in systems containing various mole percentages of SO 4 2− and Cl − indicated that Cl − did not inhibit iron oxidation but that SO 4 2− was required. Sulfate could be partially replaced by HPO 4 2− and HAsO 4 2− but not by BO 3 − , MoO 4 2− , NO 3 − , or Cl − ; formate and MoO 4 2− inhibited iron oxidation.