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Project Progress

Early Microbial Ecosystems (dm)

We are investigating the microbial populations and ecological processes that influence adaptation and evolution, and that create signatures of life (e.g., biomarkers such as gases, chemical compounds and morphologic features in sediments). In microbial mats at Guerrero Negro, Mexico, the budgets of oxygen and carbon have been found to vary between subtidal and intertidal mats, reflecting, in part, differences between the relative importance of oxic respiration versus sulfate respiration during organic degradation. Significant methane production occurred in unexpected places, such as the near-surface layers of subtidal mats and in the presence of high sulfate concentrations. Substantial hydrogen production occurred in mat surface layers, and is perhaps attributable to fermentation and also nitrogenase activity. Such hydrogen fluxes indicate that benthic microbial ecosystems might have played a significant role in determining the oxidation state of the Earth’s early atmosphere. The budgets of volatile sulfur gases, such as dimethyl sulfide, indicate that a delicate balance exists between biological and nonbiological processes of production and oxidation. A variety of low molecular weight thiol biomarkers was catalogued. Green nonsulfur bacteria from Yellowstone and Guerrero Negro mats revealed a diverse, more deeply divergent population of phototrophs than previously represented by Chloroflexus spp. The roles played by ultraviolet light in the structure, function and evolution of cyanobacteria was extensively summarized in a published review article. The Ames greenhouse facility “Archean Gardens” was enhanced to create important research opportunities involving samples collected on field trips and involving information systems technology at Ames. Long-term monitoring of mats transplanted from Baja California indicates that this facility can successfully maintain hypersaline mats in their near-original state for several months after field collection. Lithified laminae in Bahamian carbonate stromatolites are formed by biofilm communities that alternately dissolve and precipitate carbonate during early diagenesis. Laminated stromatolitic fabrics arise due to successions between different types of biofilm communities. Recent observations of the phylogeny of photopigments, together with the geologic record of stromatolites, indicate that anoxygenic phototrophic bacteria arose sometime prior to 2.8 Ga ago, and prior to the development of cyanobacteria.