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Abstract

Extremophiles can reveal the origins of life on Earth and the possibility of life elsewhere. Yet, most identified extremophiles are single-cell microbes, leaving gaps in our knowledge concerning the origins, or habitable limits, of multicellular organisms. Here, we report the recovery of roundworms (nematodes) from the Great Salt Lake, UT, a terminal lake referred to as “America’s Dead Sea” due to its extreme salinity. Phylogenetic divergence and comparison to sampling efforts from Owens Lake, an analogous terminal saline lake in the Great Basin, suggest that they represent multiple previously undescribed species of Monhysteridae, the dominant nematode family in the abyssal zone and deep-sea hydrothermal vents. Nematodes in the GSL are specifically enriched in microbialites – organosedimentary structures which were once abundant on early Earth. Nematode:bacteria asso- ciations within microbialites hint at convergent mechanisms of survival and adaptation, and may reflect ancient animal:microbe interactions.