A new moderately thermophilic proteolytic anaerobe, strain U, was isolated from mesophilic granular methanogenic sludge. The cells were spore-forming, motile rods that were 0.4 μ.m wide and 2.4 to 4 μ.m long and stained gram negative. Electron micrographs of thin sections revealed the presence of an atypical gram-positive cell wall. Optimum growth occurred at 55°C and at pH values between 7.0 and 7.5, with a doubling time of 30 min. The DNA base ratio of guanine plus cytosine was 31 mol%. The bacterium fermented proteins mainly to acetate, hydrogen, formate, and branched-chain fatty acids. Several amino acids, including glutamate, aspartate, arginine, histidine, threonine, methionine, and branched-chain amino acids, were also utilized. Glutamate was degraded to acetate, formate, hydrogen, and alanine. In addition, the strain degraded carbohydrates, including glucose, fructose, mannose, cellobiose, and starch, to acetate, ethanol, formate, lactate, and hydrogen. The results of a 16S rRNA sequence analysis phylogenetically placed strain Uin the low-guanine-plus-cytosine-content subgroup of the gram-positive phylum. We propose to classify the described strain in the genus as a new species, . The type strain of , strain U, has been deposited in the Deutsche Sammlung von Mikroorganismen as strain DSM 10124.


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