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J Bacteriol. 1969 August; 99(2): 552-557
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Kinetic Studies of Iron Oxidation by Whole Cells of Ferrobacillus ferrooxidans

^a Department of Bacteriology and Botany, Syracuse University, Syracuse, New York 13210

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 K_m for iron oxidation to be 5.4 x 10^–3M in an unbuffered system and 2.2 x 10^–3M in the presence of ß-alanine-SO₄^2– buffer. Glycine and ß-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 SO₄^2– 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 SO₄^2– and Cl^– indicated that Cl^– did not inhibit iron oxidation but that SO₄^2– was required. Sulfate could be partially replaced by HPO₄^2– and HAsO₄^2– but not by BO₃^–, MoO₄^2–, NO₃^–, or Cl^–; formate and MoO₄^2– inhibited iron oxidation.

¹ Present address: Department of Microbiology, University of Virginia Medical School, Charlottesville, Va.

² Present address: Department of Microbiology and Immunology, Duke University Medical Center, Durham, N.C. 27706.

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