Production of Hydrogen Sulfide from Tetrathionate by the Iron-Oxidizing Bacterium Thiobacillus ferrooxidans NASF-1

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When incubated under anaerobic conditions, five strains of Thiobacillus ferrooxidans tested produced hydrogen sulfide (H_2S) from elemental sulfur at pH 1.5. However, among the strains, T.ferrooxidans NASF-1 and AP19-3 were able to use both elemental sulfur and tetrathionate as electron acceptors for H_2S production at pH 1.5. The mechanism of H_2S production from tetrathionate was studied with intact cells of strain NASF-1. Strain NASF-1 was unable to use dithionate, trithionate, or pentathionate as an electron acceptor. After 12 h of incubation under anaerobic conditions at 30℃, 1.3 μmol of tetrathionate in the reaction mixture was decomposed, and 0.78 μmol of H_2S and 0.6 μmol of trithionate were produced. Thiosulfate and sulfite were not detected in the reaction mixture. From these results, we propose that H_2S is produced at pH 1.5 from tetrathionate by T.ferrooxidans NASF-1, via the following two-step reaction, in which AH_2 represents an unknown electron donor in NASF-1 cells. Namely, tetrathionate is decomposed by tetrathionate-decomposing enzyme to give trithionate and elemental sulfur (S_4O_6^<2->→S_3O_6^<2->+S^0, Eq.1), and the elemental sulfur thus produced is reduced by sulfur reductase using electrons from AH_2 to give H_2S (S^0+AH_2→H_2S+A, Eq.2). The optimum pH and temperature for H_2S production from tetrathionate under argon gas were 1.5 and 30℃, respectively. Under argon gas, the H_2S production from tetrathionate stopped after 1 d of incubation, producing a total of 2.5 μmol of H_2S/5 mg protein. In contrast, under H_2 conditions, H_2S production continued for 6 d, producing a total of 10.0 μmol of H_2S/5 mg protein. These results suggest that electrons from H_2 were used to reduce elemental sulfur produced as an intermediate to give H_2S. Potassium cyanide at 0.5 mM slightly inhibited H_2S production from tetrathionate, but increased that from elemental sulfur 3-fold. 2, 4-Dinitrophenol at .0.5 mM, carbonylcyanide-m-chlorophenyl- hydrazone at 0.01 mM, mercury chloride at 0.05 mM, and sodium selenate at 1.0 mM almost completely inhibited H_2S production from tetrathionate, but not from elemental sulfur.
社団法人日本生物工学会の論文
2000-08-25

Production of Hydrogen Sulfide from Tetrathionate by the Iron-Oxidizing Bacterium Thiobacillus ferrooxidans NASF-1

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