Molecular ecology of microbial communities involved in carbon, nitrogen, and sulfur cycling. Application and development of combined molecular, metagenomic, and isotopic methods for relating uncultured microorganisms to biogeochemical processes and understanding interspecies interactions. Specific research interests include microbial community structure and function in deep subsurface habitats, deep sea marine sediments, oil and gas seeps, and early Earth analog environments, with specific emphasis on syntrophic interactions involved in methane production and consumption.