title: Sulfite oxidation by iron-grown cells of Thiobacillus ferrooxidans at pH 3 possibly involves free radicals, iron, and cytochrome oxidase.
abstract: Thiobacillus ferrooxidans cells grown on ferrous iron oxidized sulfite to sulfate at pH 3, possibly by a free radical mechanism involving iron and cytochrome oxidase. A purely chemical system with low concentrations of Fe3+ simulated the T. ferrooxidans system. Metal chelators, ethylenediamine tetraacetic acid (EDTA), 4,5-dihydroxy-1-3-benzene disulfonic acid (Tiron), o-phenanthroline, and 2,2'-dipyridyl, inhibited both sulfite oxidation systems, but the T. ferrooxidans system was inhibited only after the initial brief oxygen consumption. EDTA and Tiron, strong chelators of Fe3+, inhibited the oxidation at lower concentrations than o-phenanthroline and 2,2'-dipyridyl, strong chelators of Fe2+. Inhibition of Fe3+-catalyzed sulfite oxidation by EDTA and Tiron was instant, but the inhibition by o-phenanthroline and dipyridyl was briefly delayed, presumably for the reduction of Fe3+ to Fe2+. Mannitol, a free radical scavenger, inhibited both systems to the same extent. Cyanide and azide inhibited only the T. ferrooxidans system, suggesting a role of cytochrome oxidase. It is proposed that sulfite is oxidized by a free radical mechanism initiated by Fe3+ on the cell surface of T. ferrooxidans. Cytochrome oxidase is possibly involved in the regeneration of Fe3+ from Fe2+ by the normal Fe2+-oxidizing system of T. ferrooxidans.
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Harahuc
authors.forename: I
authors.initials: I
authors.lastname: Suzuki
mesh_terms: D000143:Acids; D003576:Electron Transport Complex IV / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism*; D007502:Iron Chelating Agents / Q000494:pharmacology; D010084:Oxidation-Reduction; D013431:Sulfates / Q000378:metabolism; D013447:Sulfites / Q000378:metabolism*; D013855:Thiobacillus / Q000378:metabolism*; D015091:beta-Alanine / Q000378:metabolism
chemical_list: D000143:Acids; D005609:Free Radicals; D007502:Iron Chelating Agents; D013431:Sulfates; D013447:Sulfites; D015091:beta-Alanine; D007501:Iron; D003576:Electron Transport Complex IV