Stahl 97-14303 Diversity and Habitat Range of Sulfate-Reducing Microorganisms The biogeochemical cycling of elements (e.g., C, N, S, P) is the most general characteristic of the biosphere. The persistence of key biogeochemical cycles through different environmental extremes is the most general question encompassed by this research. More specifically, this study will focus on one step in the sulfur cycle, dissimilatory sulfate reduction (sulfate respiration), and better define the microbial diversity associated with, and the environmental constraints on, this key process. The need for this focus was indicated by recent comparative analyses of a highly conserved enzyme in the pathway for sulfate respiration, the dissimilatory sulfite reductase (DSR), suggesting that sulfate (or sulfite) respiration is an extremely ancient metabolism, possibly predating the divergence of the three domains of life. If this is so, then the diversity of sulfate-reducing microorganisms is almost certainly poorly described. In order to more fully evaluate their diversity and activity, environments demonstrating extremes of pH, temperature, and salinity will be characterized using a DSR-based analysis in combination with complementary microbiological, molecular (165 rRNA), and functional analyses. These studies should greatly expand understanding of the evolutionary origins of organisms mediating this key step in the sulfur cycle and the roles they play in contemporary ecosystems. This project, which is being supported by the Division of Environmental Biology, the Chemistry Division, and the Office of Multidisciplinary Activities of the Mathematical and Physical Sciences Directorate.
