Bacterially driven anaerobic sulfide oxidation by manganese oxide reduction studied in Sulfurimonas spp. (ANAMARE)

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The redox reaction of anaerobic sulfide oxidation by manganese oxide reduction has been repeatedly suggested as a possible energy source for bacteria, but all earlier attempts to enrich for microorganisms with this particular metabolism failed. In this project we propose to study a newly isolated bacterial strain, which is growing lithoautotrophically with sulfide or thiosulfate as electron donor and manganese(IV) oxide as sole electron acceptor. The isolate originates from the suboxic zone of the central Black Sea and belongs to the genus Sulfurimonas. This genus is known to be abundant in marine redoxclines, but all strains obtained earlier couple anaerobic sulfide oxidation with denitrification. First experiments revealed, that the bacterial mediated reaction between sulfide and manganese oxide, carried out by the new strain, is at least 3-5 times faster than the chemical reaction. In the course of this project, we plan to characterize the growth of the new strain in depth e.g. in terms of growth rate, growth efficiency and accumulation of intermediates such as Mn(III) and S0 in the medium. Further on, we want to gain all information, which is necessary to understand the autecology of this species and define it's ecological niche. This will include e.g. studies addressing the use of alternative electron donors and acceptors, the use of organic carbon sources, nitrogen fixation, motility and optimal growth conditions in terms of pH, salinity and temperature. With this information we aim to validly describe the new strain and deposit it in the German culture collection. Last not least we plan to sequence the genome of the strain and conduct a comparative genomic and physiological study with 3 other Sulfurimonas spp., for which both a pure culture and the complete genome sequences are available. Thereby, we can get a first impression on how wide spread this new anaerobic sulfide oxidation might be within the genus Sulfurimonas and most importantly we can search for indicative genes involved in this metabolism. In combination with experimental work, the genomic analysis will focus on the mode by which insoluble manganese oxide can be used as electron acceptor.