Mineral Microbiomes Entombed in Great Salt Lake Gypsum: Considerations for Martian Evaporites.

Abstract

Modern Great Salt Lake, UT, United States, is what remains after the extensive evaporation of Pleistocene Lake Bonneville, which makes this site an appropriate analog to ancient martian lacustrine systems. Today, evaporite minerals surround the lake, including recently precipitated displacive gypsum selenite crystals. Our hypothesis was that hydrated clay solid inclusions within the gypsum would support microbial life with water and nutrients, while the mineral encasement would provide protection from ultraviolet light and temperature fluctuations. Our data demonstrate a complex microbial community that thrives in the clay-rich inclusions within the gypsum crystals. This mineral microbiome includes archaea and fungi, but most notably an immense number of bacterial species from the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Evidence of primary producers (cyanobacteria and microalgae) that have the capacity for diverse metabolisms suggests the possibility of an entombed ecosystem with trophic levels, energy currencies, and connected metabolisms. X-ray diffraction analyses of the sediment in which the gypsum formed show the clay fraction mostly comprises discrete and randomly interstratified illite and smectite, along with lesser amounts of kaolinite and chlorite. The methods developed here for modern gypsum can be extended to studies of ancient minerals on Earth as well as hydrated sulfate minerals on Mars.