Abstract
A mutant devoid of cytochrome c-554 (CT0075) in Chlorobium tepidum (syn. Chlorobaculum tepidum) exhibited a decreased growth rate but normal growth yield when compared to the wild type. From quantitative determinations of sulfur compounds in media, the mutant was found to oxidize thiosulfate more slowly than the wild type but completely to sulfate as the wild type. This indicates that cytochrome c-554 would increase the rate of thiosulfate oxidation by serving as an efficient electron carrier but is not indispensable for thiosulfate oxidation itself. On the other hand, mutants in which a portion of the soxB gene (CT1021) was replaced with the aacC1 cassette did not grow at all in a medium containing only thiosulfate as an electron source. They exhibited partial growth yields in media containing only sulfide when compared to the wild type. This indicates that SoxB is not only essential for thiosulfate oxidation but also responsible for sulfide oxidation. An alternative electron carrier or electron transfer path would thus be operating between the Sox system and the reaction center in the mutant devoid of cytochrome c-554. Cytochrome c-554 might function in any other pathway(s) as well as the thiosulfate oxidation one, since even green sulfur bacteria that cannot oxidize thiosulfate contain a cycA gene encoding this electron carrier.
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Abbreviations
- cyt:
-
Cytochrome
- MOPS:
-
3-(N-morpholino)propanesulfonic acid
- RC:
-
Reaction center
- Sox:
-
Sulfur oxidation
- SQR:
-
Sulfide:quinone reductase
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Acknowledgments
We thank Prof. Keiichi Fukuyama, Osaka University, for his participation in stimulating discussions and for his support during this study, and Prof. Susumu Takakuwa, Kyoto Women’s University, for his technical advice to estimate the quantity of sulfur compounds. We also thank Mr. Hirofumi Omori of Osaka University for his technical assistance with nucleotide sequencing. The study was financially supported by Grants-in-Aid for Scientific Research (C) (No. 19614008) (to H.O.) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan and by a postdoctoral fellowship from the Japan Society for the Promotion of Science (No. 181481 to Y.T. and No. 183495 to J.H.).
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Azai, C., Tsukatani, Y., Harada, J. et al. Sulfur oxidation in mutants of the photosynthetic green sulfur bacterium Chlorobium tepidum devoid of cytochrome c-554 and SoxB. Photosynth Res 100, 57–65 (2009). https://doi.org/10.1007/s11120-009-9426-2
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DOI: https://doi.org/10.1007/s11120-009-9426-2