Uncovering the functional role and the ecology of uncultivated Euryarchaeota, key Archaea in aquatic ecosystems – EUREKA

The main objective of this project is to uncover the role and the global ecological importance of members of the Euryarchaeota phylum in aquatic ecosystems. Euryarchaeota, together with Thaumarchaeota, are the two main phyla belonging to the Archaea. Archaea were seen as specialist microorganisms that thrive in habitats of elevated temperature, low pH, high salinity, or strict anoxia. However, their importance in the functioning of oxic aquatic ecosystem has appeared clearly in recent years. Thaumarchaeota (previously known as Crenarchaeota) in particular are now recognized as key players in oxidizing ammonia and can outcompete the bacteria in the nitrogen cycle. In contrast to the effort put into understanding the relevance of Thaumarchaeota in aquatic habitats, basically nothing is known about the metabolisms and the ecology of uncultivated Euryarchaeota. This lack of information is critical as the high number of Euryarchaeota, that are often more abundant than Thaumarchaeota in aquatic ecosystems, suggests a pivotal ecological role for these microorganisms. The recent years have, however, seen advances regarding the biodiversity, and the spatial and temporal dynamics of their communities, but the role of these enigmatic microbes remains unknown. The objective of this project is thus to uncover the metabolisms, the distribution and the activity of the most common uncultured aquatic Euryarchaeota groups. We will target the Group II (subgroups a and b) that is particularly abundant in marine systems, and the LDS and RC-V groups that are often found in freshwater ecosystems. The technological aim of this unique project is to combine an array of state of the art methods with an approach going from the molecular to the community level, and from in silico data to environmental samples. We will use the complementary approaches of data mining, single cell genomic and environmental metagenomics to build a broad and solid base to bring new knowledge on the ecology of Euryarchaeota. This knowledge will be then channeled back to the field for an in situ assessment of the ecological importance of Euryarchaeota.