Thiosulfate oxidation in sulfur-storing bacteria
Final Report Abstract
Thiosulfate is a stable and environmentally abundant sulfur compound of intermediate oxidation state and fulfils an important role in the natural sulfur cycle. In a number of facultatively chemo- and photolithotrophic organisms like Paracoccus pantotrophus or Rhodovulum sulfidophilum thiosulfate is oxidized to sulfate without the liberation of any intermediates while in many other environmentally important sulfur oxidizers including the phototrophic green and purple sulfur bacteria and chemotrophic sulfur oxidizers like Beggiotoa or Thiothrix conspicuous globules of polymeric, water-insoluble sulfur accumulate as intermediates. In both groups core elements (SoxXA, SoxB and SoxYZ) of the periplasmic thiosulfate-oxidizing Sox multienzyme complex are present. The biochemical differences between the two different Sox systems were worked out using the anoxygenic phototrophic purple sulfur bacterium Allochromatium vinosum as the model organism. We developed methods for heterologous production of purple bacterial Sox proteins in Escherichia coli and finally successfully set up an assay system combining recombinant Sox protein from A. vinosum and P. pantotrophus. One very important insight gained from these experiments was that A. vinosum SoxL, a rhodanese-like protein encoded immediately downstream of soxXAK, plays an important role in recycling of SoxYZ as it increases thiosulfate depletion velocity in vitro without increasing the electron yield. We applied a genetic approach to analyze the role of the purple sulfur bacterial Sox proteins for the oxidation of sulfur compounds other than thiosulfate. We thus showed that Sox proteins are not involved in the oxidation of sulfide, at least in the presence of sulfide:quinone oxidoreductase. Sox proteins are also not required for uptake of externally added elemental sulfur. The most surprising finding was the involvement of SoxYZ in purple sulfur bacterial sulfite metabolism. A function as a periplasmic sulfite-binding protein is probable. In the course of this work we identified a new sulfite-oxidizing protein, SoeABC, in A. vinosum. It probably also plays a major role on other phototrophic and chemotrophic sulfur oxidizers. Finally, we studied regulation of sox genes in Allochromatium vinosum. We showed that the genes are expressed on a low constitutive level even in the absence of reduced sulfur compounds. Thiosulfate and possibly sulfide lead to an induction of sox gene transcription. Additional translational regulation was not apparent. Regulation of soxXAK is probably performed by a twocomponent system consisting of a multi-sensor histidine kinase and a regulator with proposed diguanylate cyclase activity.
Publications
- (2008) Inorganic sulfur compounds as electron donors in phototrophic sulfur bacteria. In Advances in photosynthesis and respiration (Govindjee, series editor), Vol. 27: Sulfur metabolism in phototrophic organisms (Hell, R., Dahl, C., Knaff, D. & Leustek, T., eds.) Springer, Dordrecht, 289-317
Dahl, C.
- (2008) Sulfur oxidation in prokaryotes,. In Encyclopedia of Life Sciences (ELS), John Wiley & Sons, Ltd., Chichester
Dahl C., Friedrich, C. G. & Kletzin, A.
(See online at https://doi.org/10.1002/9780470015902.a0021155) - (2008) Thiosulfate and sulfur oxidation in purple sulfur bacteria. In Microbial sulfur metabolism (Dahl, C. & Friedrich, C. G., eds.) Springer Verlag, Heidelberg Berlin, 101-116
Grimm, F., Franz, B. & Dahl, C.
- (2009) Sulfur metabolism in phototrophic purple bacteria. In Advances in photosynthesis and respiration (Govindjee, series editor), Vol. 28: Phototrophic purple bacteria (Hunter, C. N. & Daldal, F. & Thurnauer, M. C. & Beatty, J.T., eds.) Springer, Dordrecht, 595-622
Sander, J. & Dahl, C.
- (2009) Sulfur metabolism in phototrophic sulfur bacteria. Adv. Microb. Physiol. 54, 103-200
Frigaard, N. U. & Dahl, C.
- (2009). Interaction between Sox proteins of two physiologically distinct bacteria and a new protein involved in thiosulfate oxidation. FEBS Lett. 583, 1281-1286
Welte, C., Hafner, S., Krätzer, C., Quentmeier, A. T., Friedrich, C. G. & Dahl, C.
- (2011) Complete genome sequence of Allochromatium vinosum DSM 180T. Stand. Genomic Sci. 5, 3
Weissgerber, T., Zigann, R., Bruce, D., Chang, Y.-J., Detter, J. C., Han, C., Hauser, L., Jeffries, C. D., Land, M., Munk, A. C., Tapia, R. & Dahl, C.
(See online at https://dx.doi.org/10.4056%2Fsigs.2335270) - (2011) Regulation of dissimilatory sulfur oxidation in the purple sulfur bacterium Allochromatium vinosum. Front. Microbio. 2, 51
Grimm, F., Franz, B. & Dahl, C.
(See online at https://doi.org/10.3389/fmicb.2011.00051)
