Extremophile Microorganism Communities In Sulfates and Other Sulfur Minerals: Models for Mars and Other Solar System Bodies

The presence of various sulfates on the Martian surface and suggestions of significant sulfur presence on icy bodies like Europa has generated much astrobiological interest in analogous terrestrial Earth environments. Numerous active sulfur-transforming organisms live in sulfur rich environments in both the surface and subsurface. They are involved in processes that either degrade or precipitate sulfates. Our team has studied organisms and their associated mineralogies in several salient environments: 1) a sulfuric acid dominated cave system where the biological activity is integral to the precipitation of sulfates, 2) microbial communities in a briny sulfur-rich iron mine environment that appear to be mediating deposit of microcrystalline jarosite, 3) organisms that utilize copper sulfides producing copper oxides and sulfates as byproducts of that transformation, 4) gypsum fracture microbial communities in the Gypsum Plain area of southeastern NM and west Texas, and 5) microorganism remains, possible DNA and living organisms from giant hydrothermal selenite crystals in a Mexican mine/cave system.

The effects of microorganisms in these systems include physical proximity of organisms with mineral grains, transformations from amorphous to crystalline mineral phases in living materials, and isotopic fractionation indicative of microbial processes. Such Earth-based microbial communities are of relevance to potential biology and mineralogy of Mars and useful as a comparison to materials that will be studied on future life detection and other missions. In order to meet the standards of proof for science in Earth extreme environments, we must employ a variety of labor-intensive analyses beyond the foreseeable scope aboard near-term missions. As a byproduct, we are amassing a library of textures, microbial structures, and mineralogical compositions that can be associated on Earth unequivocally with biological activity. Such a field guide of properties can help guide life-detection mission strategies in the future to select samples of potentially great astrobiological significance.