- CoDL - Prony Hydrothermal Field - New Caledonia
Serpentinization and associated geochemical reactions are important sources of energy and organic carbon for subsurface habitats, but very few studies have explored the distribution, ecology, and evolution of serpentinite-hosted microbial communities. The most fully characterized example of a serpentinization-driven microbial ecosystem is that found in the carbonate chimneys of the Lost City hydrothermal field, near the Mid-Atlantic Ridge, which have been the focus of many interdisciplinary studies that aim to understand the relationship between deep carbon, deep energy, and deep life. Furthermore, such systems have been highlighted as potentially providing important clues about the origins and early evolution of life. Until recently, the Lost City carbonate chimneys were thought to be a unique microbial ecosystem, drastically different from any that had been discovered. However recently, similar hydrothermal chimneys in the Bay of Prony, New Caledonia, have been found to be analogous to the Lost City chimneys in many respects, while at the same time providing an interesting point of comparison. In the Bay of Prony, New Caledonia, carbonate chimneys vent 22-43°C, pH 11 fluids rich in hydrogen and methane at shallow depth. The fluids represent mixing of seawater with low-salinity groundwater derived from continental ultramafic rock. In each chimney, bacterial richness was at least an order of magnitude higher than that of archaea, in agreement with previous studies at Lost City. Interestingly, many sequences were affiliated with thermophilic anaerobic organisms related to marine and terrestrial hydrothermal systems, despite the moderate temperatures of chimney fluids. Remarkably, the archaeal community was dominated by uncultured Methanosarcinales represented by three phylotypes, of which one is found in the Lost City chimneys and another is found in a continental serpentinite site (The Cedars, California). The most abundant and diverse bacterial communities were mainly composed of Chlorofexi, Deinococcus-Thermus, Proteobacteria, and Firmicutes, the later two phyla containing phyloptypes also common to either Lost City or the Cedars. Therefore, Prony site represents an interesting transition between continental serpentinite springs. In spite of the considerable interest to the microbiology of serpentinite ecosystems it appears that the large majority of the microorganisms thriving in this extreme environment resisted cultivation attempts because until very recently no isolate has been described. Culture-based approaches of representative isolates, allowing detailed and reproducible physiological and genomic studies, constitute a key step in understanding the ecophysiological properties of these extremophiles, that is how they adapted to such harsh conditions and how their metabolic activities potentially interact with the geochemistries of their environments. The importance of such studies is exemplified by the recent description of a new genus of alkaliphilic betaproteobacteria, Serpentinomonas, isolated from The Cedars springs. This CoDL research aims to sequence the genome of the first alkaliphilic bacteria representative of a marine serpentinization-driven ecosystem.