9615356 Stahl This research will extend studies in microbial ecology of sediment biogeochemistry in Lake Michigan. The first component of the research will continue to characterize site conditions which will serve as a comparative data base for studies at additional sites in this Lake. The PIs will continue to determine geochemical profiles to use as baseline criteria for relating the contribution of different microbial populations to organic mineralization via different respiratory processes. Quantification and identification of populations using group-specific hybridization probes and comparative rRNA sequencing will remain the principal organizing framework. This research will continue to relate individual population abundance to seasonal variation in sediment processes thought to be governed primarily by changes in organic matter input. To further understanding of carbon and electron flow in this complex habitat, the PIs will combine two independent molecular measures, group-specific DNA probes and lipid biomarkers. This will serve as a critical comparison of methods, provide independent measures of total active biomass, and serve as a foundation for subsequent stable isotope measurements. Stable isotope composition of signature lipid components that can be clearly associated with well-defined phylogenetic groups will be used to infer the carbon source for individual groups. Preliminary studies suggest that this will provide very useful information about the trophic relationships of individual sediment populations. More standard microbiological methods of enumeration will be used for comparison. The emphasis will be on anaerobic process, although recent observations have prompted continued analysis of a novel archaeal population. In the longer term, these studies should also contribute to establishing the connections between sediment and water column activities, for example, how sediment microbial populations may affect or regulate the production of organic matter in the overlying water .
