This seminar is part of the EAI on-line seminars
Determining the exact physicochemical extremes at which microbial life can still thrive is challenging. In these usually low-biomass environments, external contamination or the abiotic formation of cell-looking structures may constitute important confounding factors. In this talk, we will explore the limits of life at the polyextreme geothermal site of Dallol. Dallol is a proto-volcano located in the North of the Danakil Depression in Ethiopia. Raising from the bottom of a salt desert, the Dallol dome is subject to extensive degassing and hydrothermal activity. Together with an interdisciplinary team, we have been studying the presence and diversity of life in various systems displaying different combinations of extreme conditions at and around the Dallol area. While several of these systems harbor specialized microbial communities dominated by halophilic archaea, our results strongly suggest that microbial life is absent from highly chaotropic hypersaline lakes and from the hyperacidic (pH<0), hypersaline (>30% weight/volume) and, sometimes hot (up to ~110°C) brines of the Dallol dome. I will show that aerosols actively transport a wide diversity of prokaryotic and eukaryotic cells over Dallol but that, upon contact with the chaotropic hyperacidic brine, cells and DNA are rapidly degraded. I will also show the extant occurrence of mineral (mostly silica-based) biomorphs that unspecifically bind fluorescent probes and dyes. Our study highlights the need for controls and the consideration of alternative abiotic explanations before safely concluding on the presence of life in polyextreme terrestrial or extraterrestrial systems. The occurrence of lifeless brines on the surface of our planet questions the idea of liquid water on a planet’s surface as the only habitability criterion.