Unravelling the formation of unique modern stromatolites by taxonomic and functional analysis: implications for the early evolution of life

Lake Untersee in East Antarctica represents a unique ice-sealed ecosystem with ultra-oligotrophic waters, high pH and it is tightly sealed from the environment except for the penetration of sunlight (5%). This habitat serves as an ecological analog of early Earth and other worlds in our solar system characterized by thick permanent ice covers, such as Enceladus, Europa and ancient ice-covered lakes on Mars. It is the only known freshwater lake hosting large conical modern stromatolites at its bottom. These structures consist of a thin layer of oxygenic photosynthetic Bacteria covering alternating laminations of sediment and microbially derived organic matter. It is still unknown why these large conical stromatolites occur exclusively at this site. I propose to use an integrative approach to determine taxonomy and functionality of these structures to shed light on the mechanisms driving their formation. Investigations to understand the microbial assemblages as well as functional potential of communities will be done using in-depth environmental taxonomic, metagenomic and imaging analyses. This research will investigate the role played by Bacteria, Eukarya and Archaea in the formation of conical stromatolites as well as understanding whether these structures are characterized by a core taxonomy and functionality. Microbiome composition and function of the stromatolites of Lake Untersee will be compared with that of microbial structures in similar Antarctic lakes to understand the effect of environment and geography. SEM and confocal laser scanning will be used to explore physical interactions between microbes and minerals in conical stromatolites and to provide information on the biogeochemical processes involved. This research will advance our knowledge on the emergence of complex structures in microbial mats and is fundamental to interpret biological influences on ancient stromatolites.