A new anaerobic, proteolytic, moderately thermophilic bacterium, strain 3RT, was isolated from a methanogenic mesophilic reactor treating protein-rich wastewater. The cells were Gram-negative, non-spore-forming, non-motile rods. The DNA base composition was 43 mol% G + C. The optimum pH and temperature for growth were 7.0 and 55 degrees C respectively. The bacterium fermented gelatin, casein, bovine albumin, peptone and yeast extract. Glucose, fructose, sucrose, maltose and starch were poorly fermented. The major fermentation products from glucose were acetate, CO2 and H2 and, from gelatin, propionate was also detected. Growth on glucose was stimulated by thiosulfate, which was reduced to sulfide. Sulfate and nitrate were not reduced. 16S rRNA gene analysis revealed that the isolated bacterial strain was phylogenetically related to Coprothermobacter proteolyticus (96.3% sequence similarity), the only known species within the genus. DNA-DNA hybridization analysis demonstrated a very low level of homology, indicating that the isolated strain and C. proteolyticus were not related at species level. Therefore, it is proposed to classify the described strain in the genus Coprothermobacter as a new species, Coprothermobacter platensis. The type strain of C. platensis is strain 3RT (= DSM 11748T).