MELISSA is a micro-organism based ecosystem, designed to recycle waste products, primarily through anaerobic processes. In order to have an efficient cycling of elements such as C, N, S, the degradation of biological polymers, present in the MELISSA substrate, is a crucial step. In this paper batch experiments to evaluate the cellulolytic capacity of Clostridium thermocellum and Clostridium thermosaccharolyticum are described. A thermophilic proteolytic strain was isolated from a dry anaerobic composting reactor digest. The strain was taxonomically studied and identified as Coprothermobacter proteolyticus I8, a strictly anaerobic bacterium. Five proteins and ten carbohydrates were tested as a substrate for the isolated strain. Growth of the three strains on rat faeces (= test substrate) was monitored. Both Clostridium strains failed to grow in the substrate whereas Coprothermobacter could grow. The proteolytic activity of Coprothermobacter proteolyticus should be improved.