Bioremediation and resource recovery from wastes and wastewaters are central issues for sustainable development. Anaerobic digestion is a cost-effective way to treat wastewaters, resulting in the production of biogas (a fuel gas). Propionate and butyrate are key intermediates in the anaerobic conversion of complex organic materials; these intermediates are generally degraded by syntrophic communities of acetogenic bacteria and methanogenic archaea and/or sulfate-reducing bacteria (SRB). Syntrophomonas species are known for their ability to degrade butyrate and longer chain fatty acids. Syntrophomonas wolfei is the best studied fatty-acid degrading syntrophic bacterium and is able to utilize saturated fatty acids with four to eight carbons. Saturated and unsaturated longer chain fatty acids (up to 18 carbon atoms) can be degraded by, for example, Syntrophomonas zehnderi – a strain previously isolated at our lab. Propionate conversion is known to be performed by bacteria from the genera Syntrophobacter, Pelotomacullum and Smithella; they use either the methylmalonyl-CoA pathway (Syntrophobacter and Pelotomaculum) or the dismutation pathway (Smithella) for propionate oxidation. Smithella species are especially found in oil-contaminated environments and seem to play an important role in alkane degradation. The aim of this project is to study syntrophic interactions in the conversion of fatty acids to get insight into physiological properties. To accomplish this, we will perform: (1) Physiological (proteomics) and kinetic studies of co-cultures of syntrophs (Pelotomacullum and Syntrophomonas species) with methanogens or syntrophs with sulfate-reducing bacteria, (2) Genomic comparison of Pelotomaculum species and Smithella propionica, and (3) Genomic and physiological studies to elucidate the role of Smithella species in alkane degradation.