Clostridium proteoclasticum sp. nov., a novel proteolytic bacterium from the bovine rumen

A novel proteolytic bacterium was isolated from rumen contents of New Zealand cattle grazing fresh forage and was designated strain B316(T) (T = type strain). Strain B316(T) cells were straight to slightly curved rods (width, 0.4 to 0.6 microns; length, 1.3 to 3.0 microns) that were gram-positive and possessed a single subterminal flagellum. This isolate did not produce catalase, indole, ammonia, lipase, or lecithinase, or reduce nitrate, but it did produce a curd reaction with milk. Strain B316(T) was proteolytic, hydrolyzing casein and fraction I leaf protein. The crude proteinase was predominantly the serine type, but some cysteine proteinase and metallo-proteinase activities were also detected. The DNA base composition of strain B316(T) was 28 mol% G+C. A 16S ribosomal DNA sequence analysis of strain B316(T) indicated that it was most closely related to a member of clostridial cluster XIVa, viz., Clostridium aminophilum, an amino acid-fermenting organism isolated from the rumen; the similarity value was 92.2%. The results of the phenotypic characterization analysis, G+C content analysis, and phylogenetic analysis of the 16S ribosomal DNA sequence set strain B316(T) apart from all of the members of cluster XIVa. We propose that strain B316(T) should be designated a new species of the genus Clostridium, Clostridium proteoclasticum. Strain B316 is the type strain and has been deposited in the American Type Culture Collection as strain ATCC 51982.