LExEN: Life in Acid

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9978205BanfieldUnusual microorganisms thrive in hot, extremely acidic solutions associated with weathered pyrite-rich rocks. Prior work has documented a dynamic archaeal, bacterial, and eukaryotic community in 30 - 50 degrees C, pH 0 - 1.0 solutions. Reduced iron and sulfur from pyrite are key microbial energy sources. Microbes that catalyze the oxidation of Fe2+ dramatically impact sulfuric acid generation rates. Populations of lithotrophs and heterotrophs vary with temperature, solution composition, pH, and location. This project will explore how these populations change with changes in geochemical conditions and determine the specific acid and ionic strength resistance and energy generation mechanisms that allow microbial communities to exist in extremely acidic environments. In general, little is known about the identity and survival strategies of the majority of members of extremely acidiphilic microbial communities. A novel mesothermophilic iron-oxidizing archaea (Ferromonas acidiphilium) has been isolated from a field site at Iron Mountain, CA. Additional species will be isolated from samples known to contain the little studied Acidomicrobium ferrooxidans and previously recognized and new relatives of "Leptospirillum ferrooxidans". Isolates will be used in biochemical investigations. Many organisms from this site have not been identified; these will be the focus of further sequencing and isolation efforts. It is anticipated that cells will employ passive pH resistance mechanisms (involving cell membrane constituents, possibly in conjunction with S-layers). Thus, the dependence of cell wall composition (i.e., fatty acids and/or proteins) on growth conditions will be explored, and thereby possible resistance mechanisms evaluated. Prior work indicates that cytochromes other than rusticyanin (used by Thiobacillus ferrooxidans) are important for iron oxidation by bacterial and archaeal species. Relevant cytochromes will be identified in order to evaluate the diversity of energy generation mechanisms that underpin the ecosystem.