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Genomic Approach to Study the Role of Bacterioplankton in the Sulfur Cycle

Periodic Report Summary - GENS (Genomic Approach to Study the Role of Bacterioplankton in the Sulfur Cycle)

GENS has explored microbial roles controlling and processing relevant climatic gas Dimethylsuflide (DMS) and its precursor Dimethylsulfoniopropionate (DMSP) in open-ocean and coastal waters through metatranscriptomics. Additionally, bacterial roles in biogeochemical cycling of other essential elements such as phosphorous and complementary energy sources through the expression of functional geneswere surveyed.

Overall, the results indicated that DMSP supports heterotrophic activity, and depletes transcriptomes related to light-related energy generation. Genes for degradation of C3 compounds were significantly overrepresented after DMSP additions, likely reflecting the metabolism of the C3 component of DMSP. Mapping these transcripts on already known biochemical pathways indicated that both acetyl-CoA and succinyl-CoA may be common entry points of this moiety into the tricarboxylic acid cycle. In general, different gene expression patterns suggested the use of DMSP by a diversity of bacteria as both carbon and sulphur sources.

Functional studies in the Nortwestern Mediterranean (Blanes Bay Microbial Observatory) were also carried out. Different acid nucleic content communities we sorted and sequenced over two contrasted periods of the year. We showed that the evidence of high DNA-low DNA cytometric signatures cannot be viewed as active versus inactive bacteria but rather as two common life strategies found in marine waters: restricted and versatile groups, respectively.

Finally, we applied for the first time metatranscriptomics to study freshwater communities of high altitude lakes within the Limnological Observatory of the Pyrenees. Comparison with similar studies from marine systems showed that high altitude lakes have strong phosphorus limitation and are largely enriched in genes devoted to cations processing. In addition, three main mechanisms have been found to take advantage of sunlight as an extra source of energy by heterotrophic bacteria: an indirect pathway in which bacteria obtain energy through the oxidation of carbon monoxide (CO) generated by photooxidation of organic matter; and two direct photoheterotrophic mechanisms in which bacteria obtain energy through bacteriochlorophyll a (Bchl a) and proteorhodospin (prho) generated ion fluxes (electrons and protons, respectively).