A novel bacterial sulfur oxidation pathway provides a new link between the cycles of organic and inorganic sulfur compounds

Oxidation of various inorganic sulfur compounds by Thiobacillus ferrooxidans was studied, and conditions necessary for maximum respiration rates were established. Optimum oxidation of elemental sulfur occurred at pH 5.0 and gave a Qo2(N) of 726; oxidation of thiosulfate gave a maximum Qo2(N) of 514 at pH 4.0; tetra- and tri-thionate, when oxidized at pH 6.0, gave a maximum Qo2(N) of 103 and 113, respectively. Polythionates accumulated during thiosulfate oxidation, but did not during oxidation of elemental sulfur. Metallic sulfide minerals were oxidized optimally as follows: chalcopyrite, pH 2.0, maximum Qo2(N) 3200; bornite, pH 3.0, maximum Qo2(N) 450; pyrite, pH 2.0, maximum Qo2(N) 1600. Maximum temperature for oxidation of all inorganic sulfur compounds tested was 40 C.The effect of a variety of organic compounds on sulfur oxidation is presented.T. ferrooxidans requires growth adaptation on iron for maximum respiration on that substrate; however, sulfur oxidation is not inducible. Iron and sulfur can be oxidized simultaneously, giving a rate equal to the sum of the maximum rates of oxidation of the two substrates individually.

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Oxidation of inorganic sulfur compounds: Chemical and enzymatic reactions

Canadian Journal of Microbiology ◽

10.1139/w98-223 ◽

1999 ◽

Vol 45 (2) ◽

pp. 97-105 ◽

Cited By ~ 69

Author(s):

Isamu Suzuki

Keyword(s):

Sulfur Oxidation ◽

Chemical Oxidation ◽

Sulfur Compounds ◽

Enzymatic Oxidation ◽

Enzymatic Reactions ◽

Oxidation Reactions ◽

Microbial Oxidation ◽

Inorganic Sulfur ◽

Nucleophilic Cleavage ◽

Oxidation Of Sulfur Compounds

Microbial oxidation of inorganic sulfur compounds is governed by both chemical and enzymatic reactions. It is therefore essential to understand reactions possible in chemistry when we consider enzymatic reactions. Various oxidation states of sulfur atoms in inorganic sulfur compounds and chemical oxidation reactions as well as nucleophilic cleavage of sulfur-sulfur bonds are discussed. The scheme of enzymatic oxidation of sulfur compounds with S2-→> S0→> SO32-→> SO42-as the main oxidation pathway is discussed with thiosulfate and polythionates leading into the main pathway for complete oxidation to sulfate. Enzymatic reactions are related to chemical reactions and the use of inhibitors for S0→> SO32-and SO32-→> SO42-is discussed for analyzing and establishing reaction stoichiometries. The proposed pathway is supported by a variety of evidence in many different microorganisms including some genetic evidence if the oxidation steps include all the systems irrespective of oxidizing agents (O2, Fe3+, cytochromes etc.).Key words: sulfur, oxidation, chemical, enzymatic, reactions.

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Mechanism of oxidation of inorganic sulfur compounds by thiosulfate-grown Thiobacillus thiooxidans

Canadian Journal of Microbiology ◽

10.1139/w01-015 ◽

2001 ◽

Vol 47 (4) ◽

pp. 348-358 ◽

Cited By ~ 16

Author(s):

Rosemarie Jefferey Y Masau ◽

Jae Key Oh ◽

Isamu Suzuki

Keyword(s):

Sulfur Oxidation ◽

Optimal Growth ◽

Sulfur Compounds ◽

Intact Cells ◽

Thiobacillus Thiooxidans ◽

Inorganic Sulfur ◽

Sulfite Oxidation ◽

Mechanism Of Oxidation ◽

Hydroxy Quinoline ◽

In Cells

Thiobacillus thiooxidans was grown at pH 5 on thiosulfate as an energy source, and the mechanism of oxidation of inorganic sulfur compounds was studied by the effect of inhibitors, stoichiometries of oxygen consumption and sulfur, sulfite, or tetrathionate accumulation, and cytochrome reduction by substrates. Both intact cells and cell-free extracts were used in the study. The results are consistent with the pathway with sulfur and sulfite as the key intermediates. Thiosulfate was oxidized after cleavage to sulfur and sulfite as intermediates at pH 5, the optimal growth pH on thiosulfate, but after initial condensation to tetrathionate at pH 2.3 where the organism failed to grow. N-Ethylmaleimide (NEM) inhibited sulfur oxidation directly and the oxidation of thiosulfate or tetrathionate indirectly. It did not inhibit the sulfite oxidation by cells, but inhibited any reduction of cell cytochromes by sulfur, thiosulfate, tetrathionate, and sulfite. NEM probably binds sulfhydryl groups, which are possibly essential in supplying electrons to initiate sulfur oxidation. 2-Heptyl-4-hydroxy-quinoline N-oxide (HQNO) inhibited the oxidation of sulfite directly and that of sulfur, thiosulfate, and tetrathionate indirectly. Uncouplers, carbonyl cyanide-m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), inhibited sulfite oxidation by cells, but not the oxidation by extracts, while HQNO inhibited both. It is proposed that HQNO inhibits the oxidation of sulfite at the cytochrome b site both in cells and extracts, but uncouplers inhibit the oxidation in cells only by collapsing the energized state of cells, ΔµH+, required either for electron transfer from cytochrome c to b or for sulfite binding.Key words: Thiobacillus thiooxidans, thiosulfate, oxidation, sulfite.

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Thiosulfate oxidation and mixotrophic growth of Methylobacterium oryzae

Canadian Journal of Microbiology ◽

10.1139/w07-057 ◽

2007 ◽

Vol 53 (7) ◽

pp. 869-876 ◽

Cited By ~ 16

Author(s):

R. Anandham ◽

P. Indiragandhi ◽

M. Madhaiyan ◽

Kyounga Kim ◽

Woojong Yim ◽

...

Keyword(s):

Novel Species ◽

Sodium Succinate ◽

Sodium Thiosulfate ◽

Sulfur Oxidation ◽

Sulfur Source ◽

Mixotrophic Growth ◽

Inorganic Sulfur ◽

Oxidation Pathway ◽

Thiosulfate Oxidation ◽

Methylobacterium Oryzae

Thiosulfate oxidation and mixotrophic growth with succinate or methanol plus thiosulfate was examined in nutrient-limited mixotrophic condition for Methylobacterium oryzae CBMB20, which was recently characterized and reported as a novel species isolated from rice. Methylobacterium oryzae was able to utilize thiosulfate in the presence of sulfate. Thiosulfate oxidation increased the protein yield by 25% in mixotrophic medium containing 18.5 mmol·L–1of sodium succinate and 20 mmol·L–1of sodium thiosulfate on day 5. The respirometric study revealed that thiosulfate was the most preferable reduced inorganic sulfur source, followed by sulfur and sulfite. Thiosulfate was predominantly oxidized to sulfate and intermediate products of thiosulfate oxidation, such as tetrathionate, trithionate, polythionate, and sulfur, were not detected in spent medium. It indicated that bacterium use the non-S4intermediate sulfur oxidation pathway for thiosulfate oxidation. Thiosulfate oxidation enzymes, such as rhodanese and sulfite oxidase activities appeared to be constitutively expressed, but activity increased during growth on thiosulfate. No thiosulfate oxidase (tetrathionate synthase) activity was detected.

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