A strictly anaerobic, Gram-positive, non-spore-forming bacterium was isolated from sewage sludge which grew on creatinine as sole source of carbon and energy. This new isolate, designated strain KRE 4, totally degraded creatinine via creatine, sarcosine and glycine to the products acetate, monomethylamine, ammonia and carbon dioxide. Growth on creatinine or creatine was selenium-dependent and stimulated by formate, indicating the involvement of a creatine reductase, sarcosine reductase and/or glycine reductase. This was substantiated by the fact that creatine, sarcosine and glycine were reduced by cell-free extracts. Growth on creatinine or creatine was also possible in the absence of formate, but with an increase in doubling time. The new bacterium occurred as rod-shaped cells, which exhibited an angular form (2–6 μm long and 0·7–1·1 μm wide) and showed motility by means of peritrichous flagella. The G+C content of the DNA was 30 mol%. Comparative 16S rRNA sequence analysis demonstrated that strain KRE 4represents a new subline within the genus . Due to its very restricted substrate spectrum and the inability of whole cells to utilize sarcosine and glycine as intermediates of creatine breakdown, this organism can be readily separated from currently described species of . Therefore, based on the phenotypic and phylogenetic distinctiveness of the new isolate, it is proposed that the bacterium be classified as a new species of the genus sp. nov. The type strain is KRE 4 (= DSM 6911).


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