The eukaryome of modern microbialites reveals distinct colonization across aquatic ecosystems

Microbial diversity includes bacteria, archaea, eukaryotes, and viruses; however, protists are less studied for their impact and diversity within ecosystems. Protists have been suggested to shape the emergence and decline of ancient stromatolites. Modern microbialites offer a unique proxy to study the deposition of carbonate by microbial communities due to analog status for ancient ecosystems and their cosmopolitan abundance. We examined protists across aquatic ecosystems between freshwater (Kelly and Pavilion Lake in British Columbia, Canada) and marine microbialites (Shark Bay, Australia and Highborne Cay, Bahamas) to decipher the transition with respect to diversity and composition. While factors such as sequencing technology and primer-bias might influence our conclusions, we found that at the taxonomic compositional-level, the freshwater microbialite communities were clearly distinct from the marine microbialite communities. Chlorophytes were significantly more abundant in the freshwater microbialites, while saltwater microbialites communities were primarily composed of pennate diatoms. Despite the differences in taxonomic make-up, we can infer the convergent important role of these protists to microbialite community health and function. These results highlight not only the consistency and potential role of microbialite eukaryotic communities across geographic locations, but also that other factors such as salinity seem to be the main drivers of community composition. ### Competing Interest Statement The authors have declared no competing interest.