ISOLATION AND SOME PROPERTIES OF AN IRON-OXIDIZING BACTERIUM THIOBACILLUS-FERROOXIDANS RESISTANT TO MOLYBDENUM ION

Among seventy five strains of iron-oxidizing bacteria obtained from na tural environments, only one strain, Thiobacillus ferrooxidans Funis 2 -1, grew on Fe2+-medium with 1.25 mM of sodium molybdate (Mo6+). In co ntrast, T. ferrooxidans AP19-3, the representative of Mo sensitive str ains, could not grow on Fe2+-medium with 1.0 mM of sodium molybdate. B y 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 act ual inhibitor for the iron oxidation enzyme system, especially for cyt ochrome c oxidase, Cytochrome c oxidase of Funis 2-1 was more resistan t 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 show ed a lower binding activity to Mo6+ or Mo5+ compared to AP19-3. Cytoch rome c oxidase of T. ferrooxidans has been known to catalyze the oxida tion of not only reduced mammalian cytochrome c but also Mo5+. Mo5+-ox idizing activities measured with intact cells and a purified cytochrom e c oxidase from Funis 2-1 cells were higher than those of AP19-3, sug gesting that Funis 2-1 cells can oxidize toxic Mo5+ more rapidly to ha rmless Mo6+ than AP19-3 does. Since Mo6+ is known to be chemically red uced by Fe2+ to give Mo5+ and Fe3+, the growth inhibition by sodium mo lybdate (Mo6+) observed in T. ferrooxidans is explained as follows: Mo 6+ added to Fe2+-medium is chemically reduced by Fe2+, and Mo5+ thus p roduced binds to the plasma membrane and inhibits iron oxidase, as a r esult, growth of the bacterium is stopped.