The governing position of microorganisms in biogeochemical cycles has long been appreciated, yet the ecology of the contributing natural microbial populations remains poorly resolved. This is principally a consequence of the technical and historical limitations of pure culture isolation and phenotypic classification. However, the advent of molecular systematics and newer techniques of molecular biology and recombinant DNA have markedly changed the repertoire of tools available to the microbial ecologist. It is now feasible to define microbial communities at the level of populations and even single cells. The proposed research will use and, to a more limited extent, develop phylogenetically-based molecular techniques to study the population structure of complex anaerobic communities. These studies will emphasize the characterization of methanogenic and sulfate- reducing bacterial populations. Sulfate-reducing and mentanogenic bacteria comprise anaerobic populations which perform the terminal mineralization of organic matter within the microbial communities of aquatic sediments and other anaerobic settings. They are generally considered to be in competition for substrates, the outcome of which is dependent upon the availability of sulfate as the electron acceptor. Comparative 16s rRNA sequencing will provide the framework for developing and applying analytical molecular techniques to determine the population structure of each functional group in different communities. The molecular techniques will include: 1) Selective PCR amplification, cloning and sequencing of 16s rRNA genes, and 2) Phylongentically-based hybridization probes. Differences (and similarities) in population structure within these communities will be evaluated in relationship to community activity (i.e. sulfate reduction, methanogenesis or acetate catabolism).
