~~~~~The intra-and intergeneric relationships of the genus Actinomyces were determined by comparing long 16s rRNA sequences, generated by reverse transcriptase. All species formed a phylogenetically coherent cluster in which Actimmyces bovis, A. viscosus, A. naeslundii, A. odontolyticus and A. israelii constituted genetically well defined species. A. israelii DSM 43322 (serotype 2) was not closely related to three other strains of this species (serotype 1) and, as judged from phylogenetic distances, could be accommodated within A. naeslundi, or represent a new species. In contrast to previous findings, members of the genus Actinomyces appear to be related to Bifidobacterium bifidum. Sequence information was used to develop an oligonucleotide probe for the A. israelii serotype 1 strains, which did not react with the serotype 2 strain or with rRNA from strains of eight Actinomyces species.

The phylogenetic position of Aruchnia propionica was determined by using reverse transcriptase sequencing of long regions of 16s ribosomal ribonucleic acid. Aruchnia propionica formed a distinct group with Propionibucterium freudenrekhii and Propionibacten'um ucnes but was unrelated to members of the genus Actinomyces. The retention of Aruchnia as a separate genus is unjustified. On the basis of the present analysis and previous chemotaxonomic evidence, we propose that Arachniu propionica be reclassified in the genus Propionibucterium as Propionibacterium propionicus (Buchanan and Pine) comb. nov.Thegenus Arachnia was created to accommodate organisms previously designated Actinomyces propionicus (14). Although Arachnia propionica is a relatively well-defined taxon, its affinity to other filamentous actinomycetes and progionibacteria is controversial (1, 13, 16). In terms of pathogenicity and morphology, Actinomyces propionicus resembles certain Actinomyces spp. (particularly Actinomyces israelii) (20). However, Arachnia propionica differs from Actinomyces species in producing propionic acid as one of the major end products of glucose metabolism (1,16,17). Arachnia propionica also differs from actinomyces in possessing a murein based on LL-diaminopimelic acid (12,18,23). Members of the genus Actinomyces contain lysine or phylogenetic interrelationships of microorganisms. In an attempt to clarify the phylogenetic position of Arachnia propionica we compared long stretches of its 16s rRNA primary structure with those of Actinomyces and Propionibacterium species and some other actinomycetes . ornithine or both as the diamino acid(s) (18, 23; N. Weiss, personal communication). However, the walls of Arachnia propionica are consistent with certain Propionibacterium species (12). Arachnia propionica also resembles propionibacteria in rnenaquinone composition and in possessing major amounts of iso-and anteiso-methyl branched longchain fatty acids (7,8). However, despite the close metabolic and chemical similarity of Arachnia propionica and propionibacteria, these taxa were recovered in quite separate phena in a recent numerical phenetic study (19). Currently 16s ribosomal ribonucleic acid (rRNA) sequencing is the most powerful method for determining the * Corresponding author. MATERIALS AND METHODS Actinomyces bovisvon Mikroorganismen, Braunschweig, Federal Republic of Germany. The strains were cultured anaerobically in broth containing the following components: yeast extract, 1%; Trypticase, 1%; glucose, 1%; 2.5% (wthol) cysteifiehydrochloride solution, 5%; 0.1% resazurin solution, 0.2%; and mineral salts solution, 7.5% (3). Actinomyces species and Arachnia propionica were grown at 37"C, and Propionibacterium species were grown at 30°C.The isolation of 16s rRNA and sequence determination by reverse transcriptase were performed as described previously (5). Computation of levels of homology (6), calculation of K,,, values from homology values (ll), and construction of an unrooted tree (9, 15) were done as described previou...

The intra- and intergeneric position of Propionibacterium was determined by comparing reverse transcriptase sequences of 16S ribosomal ribonucleic acid. Propionibacterium jensenii. P. thoenii and P. acidipropionici formed a phylogenetically tight cluster, while P. freudenreichii, P. acnes and P. propionicus were as remotely related among each other as each of them was to the first three species. The genus Propionibacterium represents a well defined taxon that stands isolated among other major groups of the actinomycetes. Its phylogenetic neighbours are the genera Nocardioides and Terrabacter.