MICROBIAL DIVERSITY OF OOIDS FROM GREAT SALT LAKE, UT

Ooids (laminated coated grains) are ubiquitous in the geologic record, but the processes that govern their formation are still poorly understood. Ooids are traditionally thought to form abiogenically, where calcium carbonate precipitates around a nucleus in an environment supersaturated with respect to calcium carbonate. Recent work suggests that microbial metabolism and its byproducts (e.g., proteins, extracellular polymeric substances) may enhance calcium carbonate precipitation, and has demonstrated that ooids from disparate localities shared some lipid biomarkers, suggesting a common microbiota and thus putative microbial origin. Thus, the meaning of ooids as a potential biosignature in ancient rocks remains problematic. The Great Salt Lake, UT provides an opportunity to assess the microbial community of petrogaphically identical ooids from two unique environments: a more saline North Arm and a less saline South Arm. These aragonitic ooids display alternating radial, concentric, and radial-concentric fabric. We collected ooids from Antelope Island (South Arm) and Spiral Jetty (North Arm). Using 16S rRNA gene sequencing, we compared the microbial communities of ooids from the North and South Arms. Both sites yielded low DNA concentrations. While ooids from both sites were dominated by members of Alphaproteobacteria, Gammaproteobacteria, and Betaproteobacteria, the relative abundance of the remaining OTUs was distinct to each site, indicating the diversity is not controlling precipitation in an obvious way.