Kinetic studies of iron oxidation by whole cells of Ferrobacillus ferrooxidans.

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 x 10(-3)m in an unbuffered system and 2.2 x 10(-3)m in the presence of beta-alanine-SO(4) (2-) buffer. Glycine and beta-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 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.