Isolation and Some Properties of an Iron-oxidizing Bacterium Thiobacillus ferrooxidans Resistant to Molybdenum Ion

Abstract

Among seventy five strains of iron-oxidizing bacteria obtained from natural environments, only one strain, Thiobacillus ferrooxidans Funis 2-1, grew on Fe2+-medium with 1.25 mm of sodium molybdate (Mo6+). In contrast, T. ferrooxidans AP19-3, the representative of Mo sensitive strains, could not grow on Fe2+-medium with 1.0mm of sodium molybdate. By comparing the levels of inhibition of iron oxidase and cytochrome c oxidase by Mo6+ or Mo5+, it was found that Mo5+ but not Mo6+ is an actual inhibitor for the iron oxidation enzyme system, especially for cytochrome c oxidase. Cytochrome c oxidase of Funis 2-1 was more resistant to Mo5+ than AP19-3. Mo5+, compared to Mo6+, strongly binds to both cells and the plasma membrane of T. ferrooxidans. Funis 2-1 cells showed a lower binding activity to Mo6+ or Mo5+ compared to AP19-3. Cytochrome c oxidase of T. ferrooxidans has been known to catalyze the oxidation of not only reduced mammalian cytochrome c but also Mo5+. Mo5+-oxidizing activities measured with intact cells and a purified cytochrome c oxidase from Funis 2-1 cells were higher than those of AP19-3, suggesting that Funis 2-1 cells can oxidize toxic Mo5+ more rapidly to harmless Mo6+ than AP19-3 does. Since Mo6+ is known to be chemically reduced by Fe2+ to give Mo5+ and Fe3+, the growth inhibition by sodium molybdate (Mo6+) observed in T. ferrooxidans is explained as follows: Mo6+ added to Fe2+-medium is chemically reduced by Fe2+, and Mo5+ thus produced binds to the plasma membrane and inhibits iron oxidase, as a result, growth of the bacterium is stopped. © 1997, Taylor & Francis Group, LLC. All rights reserved.