In Thiobacillus ferrooxidans AP19-3, elemental sulfur is oxidized by the cooperation of three enzymes, namely, hydrogen sulfide : ferric ion oxidoreductase (SFORase), sulfite : ferric ion ox-idoreductase, and iron oxidase. Sulfite ions are one of the products when elemental sulfur is oxidized by SFORase. Under the conditions in which sulfite ions are accumulated in the cells, use of sulfur as an energy source by this strain was strongly inhibited. So the mechanism of inhibition by sulfite ions in T. ferrooxidans AP19-3 was studied. The activities of SFORase and iron oxidase were completely inhibited by 0.8 mM and 1.5 mM NaHSO3, respectively. 14CO2 uptake into washed intact cells was also completely inhibited by 1 mM NaHSO3 when ferrous ion or elemental sulfur was used as an energy source. However, the activities of ribulose-1,5-bisphosphate carboxylase, phosphoribulokinase, and ribosephosphate isomerase measured with a cell-free extract were not inhibited by NaHSO3 at 1 mM, indicating that sulfite ions didn’t inhibit key enzymes of the Calvin cycle. Since the activity of CO2 uptake into washed intact cells was absolutely dependent on Fe2+- or S°-oxidation, mechanism of inhibition of sulfur use by sulfite ions is proposed as follows: sulfite ions inhibit SFORase and iron oxidase, as a result T. ferrooxidans AP19-3 can not obtain a carbon source for CO2 fixation and stops cell growth on sulfur—salts medium.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Agricultural and Biological Sciences(all)