Etoliko lagoon is part of a complex wetland in Western Greece extremely rich in biodiversity. The physical characteristics of Etoliko Lagoon include a permanent thermocline, halocline and anoxic conditions in the hypolimnion. This anoxic zone extends from 10m to 28m and a steep oxycline is evident between 5m and 10m. Etoliko lagoon is unique regarding: (a) the distribution of sulfates, which increases towards the bottom of the Etoliko lagoon while it decreases in all other well-known anoxic basins such as Framvaren Fjord, Cariaco Trench, Black Sea, Rogoznica Lake, and (b) the sediment of Etoliko lagoon is rich in microbial diversity as it has been discovered by 16S rRNA gene studies and single cell genomic approaches. These molecular studies from the sediment of Etoliko lagoon revealed the presence of more than 20 highly divergent representatives from bacterial and archaeal candidate phyla.

In this research proposal we plan to examine the microbial community assembly and evolutionary process in the transition from shallow to deep sediment. The results from this project will have implications for understanding microbial life in one of the largest, yet most inaccessible, ecosystems on Earth: the deep biosphere. This will be achieved by deploying a single cell genomics/metagenomics/metatranscriptomics approach, combined with a detailed 16S rRNA/ITS2 amplicon sequencing from anoxic deep sediment of Etoliko lagoon, targeting bacteria, archaea, and microalgae. The advanced molecular approach will be matched with an anaerobic culture-dependent approach, using several electron donors. This research proposal will produce first insights into the ecophysiologies of anaerobic natural organic matter degrading microorganisms, improve our understanding of the global carbon and sulfur cycle, and characterise unknown microbial communities.