Anoxygenic purple sulfur bacteria flourish in globally occurring habitats, wherever light reaches sulfidic water layers or sediments, and often grow as dense accumulations in conspicuous blooms in freshwater as well as marine aquatic ecosystems. Here they are not only major players in the reoxidation of sulfide produced by sulfate-reducing bacteria in deeper anoxic layers but also important primary producers of fixed carbon (up to 83% of primary production in lakes can be anoxygenic). The overall goal of this project is to obtain a comprehensive understanding of the metabolic network present in a globally occurring anoxygenic purple sulfur bacterium, to thereby better understand its contribution to global carbon, sulfur, and nitrogen fluxes and to obtain a solid basis for its use in the removal of sulfur compounds and biohydrogen production.
Allochromatium vinosum DSM 180T, a member of the family Chromatiaceae, is the best studied representative of this metabolic group, and a huge body of literature exists on enzymology and biochemistry of carbon, sulfur, nitrogen and hydrogen metabolism in this organism. Furthermore, methods for manipulative genetics exist for A. vinosum. This will facilitate interpretation of sequence data, allow testing of gene function predictions by mutational analysis, and lead to a complete understanding of the metabolic network in this and other purple sulfur bacteria. A. vinosum already serves as a model organism for sulfur oxidation. Comparative genomics with other types of sulfur-oxidizing bacteria, several of which have already been or are currently being sequenced by JGI, will facilitate a better understanding of the genes and processes involved in chemo- and photolithotrophic metabolisms (getting energy from inorganic chemical reactions and light, respectively), adaptation to extreme conditions, and the formation of symbioses with invertebrate hosts. Functional genomics (i.e., transcriptomics and proteomics in combination with culture experiments under defined conditions) will reveal enzymes involved in sulfur oxidation, important steps of which have still not been clarified in any sulfur-oxidizing organism. DNA microoarrays will be created to study the physiology of the organisms in natural and engineered ecosystems. This will ultimately allow improving the performance of the organism in the transfer of CO2 into biomass, in the removal of reduced sulfur compounds from waste, and in the production of biohydrogen.
Principal Investigators: Christiane Dahl (Univ. of Bonn)