A taxonomic re-evaluation of "Propionibacterium coccoides"

English: A study was undertaken to re-evaluate the systematic position of "Propionibacterium coccoides" relative to that of other classical Propionibacterium species. Two "P. coccoides" strains were evaluated by numerically relating them to the type and reference strains of the genus Propionibacterium as well as the type strain of the genus Luteococcus (as outgroup) by comparison of a wide range of phenotypic characters. Numerical clustering revealed five major groups, four of which corresponded to the existing classical species, while the fifth cluster grouped the two "P. coccoides" strains with the type strain of the species Luteococcus japonicus. These results clearly indicated that a higher degree of overall phenotypic similarity existed between L. japonicus and the "P. coccoides" strains than between the latter and the genus Propionibacterium. Using the polymerase chain reaction, the various 16S ribosomal RNA genes of the four Propionibacterium type strains, the two "P. coccoides" strains and the type strain of L. japonicus were successfully amplified. Visual differentiation between the four classical Propionibacterium type strains was possible after restriction endonuclease digestion of the peR products obtained using primers 16sP 1-16sP4 with the restriction endonucleases HaeIII and A/uI. Although a unique pattern was obtained for the two "P. coccoides" and the L. japonicus strains when compared to those as obtained for the four classical Propionibacterium type strains, differentiation between the two "P. coccoides" and the L. japonicus strains, even after the evaluation of numerous restriction endonucleases, was essentially still problematic. Due to the success obtained during the application of ribotyping as a technique to enable species differentiation within the genus Propionibacterium, this technique was also utilised during this study. The combination of the HaeII and Smal restriction endonuclease patterns resulted in the elucidation of the four classical Propionibacterium type strains as well as the two "P. coccoides" and the L. japonicus strains. A unique yet identical ribotyping profile was obtained for the two "P. coccoides" strains and the L. japonicus type strain. In an attempt to justify thephenotypic heterogeneity observed between the two "P. coccoides" strains and the L. japonicus type strain, numerous other restriction endonucleases were also evaluated using ribotyping. The two "P. coccoides" strains and the L. japonicus type strain could only be differentiated after digestion of the genomic DNA with the restriction endonuclease BstEII. The intrageneric phylogenetic relationship of the four classical Propionibacterium type strains, the two "P. coccoides" strains as well as the L. japonicus type strain and various other phylogenetic related genera was determined by comparative analysis of their 16S ribosomal RNA gene sequence data. The "P. coccoides" strains were observed to cluster together with the type strain of the genus Luteococcus in a clade which was phylogenetically clearly delineated from the cluster containing the various Propionibacterium species. This data subsequently confirmed the results obtained during the numerical analysis of the phenotypic characteristics. Finally DNA:DNA probe hybridisation was evaluated as a possible reliable species differentiation technique. Five major DNA:DNA homology groups could be distinguished. Four of these homology groups resembled the various classical Propionibacterium species, while the fifth DNA:DNA homology group consisted out of the "P. coccoides" strains and the L. japonicus type strain. The high degree of DNA:DNA homology between the "P. coccoides" strains and the L. japonicus type strain subsequently confirmed the phylogenetic analysis of the 16S rDNA sequence data. The results of this study subsequently indicate that the proposal by Vorobjeva et al. (1983) to include "P. coccoides" as a new species within the genus Propionibacterium is incorrect due to the higher degree of phenetic, molecular and phylogenetic similarity between Luteococcus japonicus and "P. coccoides" than between the latter and the genus Propionibacterium. It is subsequently proposed that the "P. coccoides" strains be putatively reclassified as Luteococcus japonicus subspecies casei and Luteococcus japonicus subspecies tyrophilus and that the genus description of Luteococcus be revised to include the phenetic and molecular description of these strains.