An obligately anaerobic, moderately thermophilic, glutamate-degrading bacterium (strain ZT) was isolated from an enrichment culture obtained from anaerobic thermophilic granular sludge. The cells were rod-shaped to filamentous and showed no motility or spore formation. The cell wall had a Gram-positive structure, which was revealed by electron microscopy. Optimum growth of the strain was observed under neutrophilic conditions at 50-55 degrees C. The doubling time of strain ZT grown in rich medium was approximately 1 h at optimal pH and temperature. Strain ZT was able to grow on a variety of organic compounds. Most carbon sources were converted to acetate, CO2, H2, and traces of propionate and lactate. Strain ZT oxidized glutamate to acetate, CO2, NH4+, traces of propionate and H2. The doubling time on this substrate was 1-6 d. The strain fermented glutamate syntrophically in co-culture with Methanobacterium thermoautotrophicum Z-245T to the same products, but the co-culture had a fourfold higher growth rate. 16S rDNA sequence analysis revealed a relationship with Thermobrachium celere, Caloramator indicus and Caloramator proteoclasticus. The G+C content was 31.7 mol%. Based on its morphological, phylogenetic and physiological characteristics, it is proposed that strain ZT should be classified in the genus Caloramator as a new species, Caloramator coolhaasii.