by Purificación López-García
Equipe Diversié et Evolution Microbiennes,
Unité d'Ecologie, Systématique et Evolution, CNRS UMR 8079,
Université Paris-Sud, France; puri.lopez@u-psud.fr
A microbial colonizer (see Fig.6) has been installed on the SN-4 just before deployment.
The pilot experience proposed here is a complement to an ongoing project initiated during the Marnaut 2007 cruise aiming at better understanding the microbial ecology of the Marmara deep plankton and sediment communities, with a particular emphasis in biogeochemical processes associated to methane seeps [Quaiser et al., 2010] and (Chevalier et al., in preparation). The discovery of anaerobic oxidation of methane (AOM) by mixed microbial consortia formed by archaea belonging to newly identified phylogenetic groups (ANME 1 to 3 groups) and sulfate reducing bacteria belonging to the Deltaproteobacteria dates back only to the beginning of the 2000s'. This hitherto unknown metabolic process linking AOM to sulfate reduction appears extensive in marine sediments of methane seep areas all around the world (for a review, see [Jorgensen & Boetius, 2007]). Very recently, the possibility that AOM is linked to manganese and iron reduction [Beal et al., 2009] as well as to nitrification (in particular the conversion of nitrite to dinitrogen) [Ettwig et al., 2010] has been shown. This highlights our limited knowledge about AOM and suggests that links, via symbioses, to other metabolic processes are possible and remain to be discovered. Microbial communities associated to marine anoxic sediments, where sulfate is relatively abundant, are dominated by deltaproteobacterial sulfate-reducers, which explains that AOM in methane seep anoxic sediments is coupled mainly to sulfate reduction. However, sediment bacterial communities are extremely rich and complex. This makes it difficult to study the real contribution of the different microbial species to these microbial AOM consortia. So far, the physical separation by magnetic beads of symbiotic assemblages has facilitated the study of those symbioses when there is a close and stable physical interaction [Brown et al., 2008].
In the present experiment, we propose to explore by molecular biology tools the diversity of microorganisms that colonize a porous inert substrate exposed for six months to methane-enriched seawater in a cold seep area in the Marmara Sea. This will allow (i) to test whether potential AOM symbiotic consortia colonizing this substrate are similar to those inhabiting the sediments or whether, on the contrary, they correspond to other kind of anaerobic methanotrophic consortia being part of methane-consuming plankton that remain to be described and (ii) to identify the first microorganisms colonizing this particular niche. If these turn out to be AOM communities similar to those inhabiting the sediments, they will constitute a natural in situ enrichment that could be subsequently studied by metagenomic approaches and compared to sediment and plankton communities from the Marmara Sea.
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