Isolation and Identification of an Iron-Oxidizing Bacterium Which Can Grow on Tetrathionate Medium and the Properties of a Tetrathionate-Decomposing Enzyme Isolated from the Bacterium

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Among 150 pure strains of iron-oxidizing bacteria obtained from natural environments, two strains, Funis 2-1 and OK1-50,had the ability to use potassium tetrathionate (K_2S_4O_6) as a sole energy source for growth. Funis 2-1 was a gram-negative, rod-shaped, acidophilic iron- and sulfur-oxidizing chemolithotrophic bacterium and had the same cytochrome composition and mean G+C content of DNA as Thiobacillus ferrooxidans, indicating that the strain is T. ferrooxidans. A tetrathionate-decomposing enzyme that catalyzes the disproportionate metabolism of 4 mol of tetrathionate into 7 mol of thiosulfate and 2 mol of sulfate was located on the plasma membrane of K_2S_4O_6-grown, but no Fe^<2+>-grown Funis 2-1 cells. Washed intact cells and cell extracts prepared from Funis 2-1 cells grown on K_2S_4O_6 medium supplemented with more than 11 mM FeSO_4 did not show K_2S_4O_6-decomposing enzyme activity. K_2S_4O_6-decomposing enzyme was purified to homogeneity from K_2S_4O_6-grown Funis 2-1 cells. The apparent molecular weight of this enzyme was estimated to be 50,000 by gel filtration, 50,000 by SDS-PAGE, and 49,600 using a time-of-flight mass spectrometer, indicating that the enzyme is monomeric. The enzyme was most active at pH 3.5 and 50°C and the activity was enhanced approximately 18 fold by a concentration of 200 mM of sulfate ion. The Michaelis constant of this enzyme for K_2S_4O_6 was 0.73 mM.
社団法人日本生物工学会の論文
1996-09-25