Isolation and Some Properties of an Iron-Oxidizing Bacterium<i>Thiobacillus ferrooxidans</i>Resistant to Bisulfite Ion

Abstract

An iron-oxidizing bacterium Thiobacillus ferrooxidans resistant to bisulfite ion (strain OK1-50) was isolated from stream water from Okayama City, Japan and characterized. When grown statically on FeSO4 · 7H2O (3%)-salts medium without sodium sulfite, OK1-50 and T. ferrooxidans strain AP19-3 had the same level of cell growth (200 x 106 cells/ml). However, when cultured in FeSO4 · 7H2O (3%)-salts medium with 5 mM sodium sulfite, OK1-50 and AP19-3 gave maximal cell yield of 105 x 106 and 35 x 106 cells/ml, respectively, suggesting that OK1-50 was much more resistant to bisulfite ion than AP19-3 is. The inhibition site of bisulfite ion on iron oxidase system is cytochrome c oxidase, which is one of the essential constituents of the iron oxidase system. Iron-oxidizing activity of AP19-3 was completely inhibited by 0.2mM bisulfite ion. In contrast, the activity of OK1-50 was not inhibited by 2mM sodium sulfite. Cytochrome c oxidase activity of AP19-3 was completely inhibited by 2 mM bisulfite ion. However, 5 mM bisulfite ion did not inhibit the activity of OK1-50. A similar level of sulfite: ferric ion oxidoreductase activity was observed in both strains. Hydrogen sulfide: ferric ion oxidoreductase activity of OK1-50 was one half of the activity of AP19-3. NADH-dependent sulfite reductase activity of OK1-50 was three times higher than that of AP19-3. These results indicate that having an iron oxidase system resistant to bisulfite ion makes strain OK1-50 much more resistant to bisulfite ion than AP19-3 is.