The objective of the proposed study is to use molecular criteria to identify obligate or synergistic associations among members of a natural anaerobic microbial biofilm community under changing environmental conditions. To achieve this objective, comparative sequencing of environmentally derived 16s ribosomal RNAs and application of phylogenetically-based hybridization probes will be used to identify and monitor the dominant members of groundwater biofilm communities that are established within laboratory bioreactor systems. In conjunction with in situ hybridization techniques, this molecular framework will be used to define interdependent relationships among community members such as those involving H2-producing bacteria (fermentative and fatty acid-and alcohol-oxidizing bacteria) and H2-consuming bacteria (methanogenic bacteria and sulfate-reducing bacteria). Bioreactor operating conditions (eg. Substrate concentration and sulfate concentration) will be altered to detect these interdependent associations by following coordinate fluctuations among selected microbial populations (using the molecular approach described above) during biofilm colonization, development and establishment of the climax community. The proposed research should provide fundamental information regarding the diversity, stability and function of natural microbial communities. Such basic information about microbial communities has thusfar been inaccessible, but constitutes the foundation for studies of microbial ecosystem perturbation and assessment of the risk associated with the release of genetically engineered microorganisms into the environment.
