CHEMOARCH · Identity and biogeochemical role of chemoautotrophic prokaryotes in aquatic ecosystems

We aim to identify relevant aquatic chemoautotrophic prokaryotes, which can play a key biogeochemical role with the capacity to fix CO2 independently of light. Although severely underestimated, chemoautotrophy can be widespread in natural systems and it can importantly participate in carbon cycling. Chemoautotrophs are highly diverse at the phylogenetical and metabolical levels, but our knowledge about both aspects is still very limited and will be assessed in this project. Firstly, we will identify active chemoautotrophs through Stable Isotope Probing with 13CO2. By this approach, we will label and isolate the nucleic acids of aquatic chemoautotrophs with 13C, and identify them through appropriate molecular tools. Large inserts of the isolated genomes will be analysed in fosmid clone libraries, in order to find genes that can shed light to the metabolic fashion of these organisms. This is particularly relevant in order to establish links between chemoautotrophy and other biogeochemical processes. We will focus on a specific group, Crenarchaoeta, which grows chemoautotrophically and could play a key role in nitrogen cycle in marine waters, but has not yet been studied in freshwater/brackish systems such as the ones we will sample. Finally, a survey of distribution and activity of chemoautotrophs will be done by the combination of in situ hybridization with specific probes and microautoradiography with 14CO2. This will allow us to quantify the amount of active cells of different groups in CO2 uptake along environmental gradients (transcending the freshwater-coastal waters boundary), and evaluate their biogeochemical relevance in aquatic ecosystems.