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Project Progress

We examine the roles played by microbial ecological processes in creating biological markers (e.g., gases, chemical compounds and morphologic features in sediments) and in influencing the adaptation and evolution of microorganisms. In microbial mats at Guerrero Negro, Mexico, the budget of oxygen and carbon varied seasonally, probably due to changes in the balance between gross and net mat productivity. Significant methane production occurred in the surface layers of subtidal mats, but production was very low in intertidal mats. Substantial hydrogen production occurred in mat surface layers, and intertidal mats generated larger fluxes than the subtidal mats. Significant concentrations of the acids lactate, acetate, formate and propionate were observed in mat porewaters. These acids did not escape into the overlying water column under oxic conditions, but they did escape under anoxic conditions. The flux of dimethylsulfide from subtidal mats was significant in June but very small in October. A variety of low molecular weight thiol biomarkers was also found. Almost half of the cyanobacteria studied synthesize 2-methyl hopanoid, which appears to be uniquely diagnostic of cyanobacteria and was recently identified by some of us in 2.7 billion year old rocks. Phormidium cyanobacteria from Yellowstone exhibit at least four clades of distinct genetic types with considerable genetic distance between them, indicating a split of >>100 million years among them. Within this assemblage are three distinct clades that correspond to different lipid biomarkers, including 2-methylhopanoid. Studies of 16SrRNA in green nonsulfur bacteria in Guerrero Negro mats revealed a previously undocumented cluster of organisms that is deeply divergent from previously-described populations. Ultraviolet light substantially affects the net production of oxygen by intertidal mats at Guerrero Negro. A microbial mat greenhouse facility was established for post-field trip ongoing research and for integration with information systems technology at Ames. Cyanobacterial culture collections are being maintained and cross-referenced to increase their accessibility to the astrobiology community. We will explore the impact of environmental parameters such as season, temperature, sunlight and oxygen availability upon the structure and function of subtidal and intertidal mats, with an emphasis on their production of biomarker compounds, including gases. We will conduct parallel genetic studies of photosynthetic populations to establish relationships between population richness, biomarkers and ecosystem function.