A taxonomic re-evaluation ofPropionibacterium coccoides

[摘要] English: A study was undertaken to re-evaluate the systematic position ofPropionibacterium coccoides relative to that of other classical Propionibacteriumspecies. Two P. coccoides strains were evaluated by numerically relating them tothe type and reference strains of the genus Propionibacterium as well as the type strainof the genus Luteococcus (as outgroup) by comparison of a wide range of phenotypiccharacters. Numerical clustering revealed five major groups, four of whichcorresponded to the existing classical species, while the fifth cluster grouped the twoP. coccoides strains with the type strain of the species Luteococcus japonicus.These results clearly indicated that a higher degree of overall phenotypic similarityexisted between L. japonicus and the P. coccoides strains than between the latterand the genus Propionibacterium.Using the polymerase chain reaction, the various 16S ribosomal RNA genes ofthe four Propionibacterium type strains, the two P. coccoides strains and the typestrain of L. japonicus were successfully amplified. Visual differentiation between thefour classical Propionibacterium type strains was possible after restrictionendonuclease digestion of the peR products obtained using primers 16sP 1-16sP4 withthe restriction endonucleases HaeIII and A/uI. Although a unique pattern was obtained for the two P. coccoides and the L. japonicus strains when compared tothose as obtained for the four classical Propionibacterium type strains, differentiationbetween the two P. coccoides and the L. japonicus strains, even after the evaluationof numerous restriction endonucleases, was essentially still problematic.Due to the success obtained during the application of ribotyping as a techniqueto enable species differentiation within the genus Propionibacterium, this techniquewas also utilised during this study. The combination of the HaeII and Smal restrictionendonuclease patterns resulted in the elucidation of the four classicalPropionibacterium type strains as well as the two P. coccoides and the L. japonicusstrains. A unique yet identical ribotyping profile was obtained for the twoP. coccoides strains and the L. japonicus type strain. In an attempt to justify thephenotypic heterogeneity observed between the two P. coccoides strains and theL. japonicus type strain, numerous other restriction endonucleases were also evaluatedusing ribotyping. The two P. coccoides strains and the L. japonicus type straincould only be differentiated after digestion of the genomic DNA with the restrictionendonuclease BstEII.The intrageneric phylogenetic relationship of the four classicalPropionibacterium type strains, the two P. coccoides strains as well as theL. japonicus type strain and various other phylogenetic related genera was determinedby comparative analysis of their 16S ribosomal RNA gene sequence data. TheP. coccoides strains were observed to cluster together with the type strain of thegenus Luteococcus in a clade which was phylogenetically clearly delineated from thecluster containing the various Propionibacterium species. This data subsequentlyconfirmed the results obtained during the numerical analysis of the phenotypiccharacteristics.Finally DNA:DNA probe hybridisation was evaluated as a possible reliable species differentiation technique. Five major DNA:DNA homology groups could bedistinguished. Four of these homology groups resembled the various classicalPropionibacterium species, while the fifth DNA:DNA homology group consisted outof the P. coccoides strains and the L. japonicus type strain. The high degree ofDNA:DNA homology between the P. coccoides strains and the L. japonicus typestrain subsequently confirmed the phylogenetic analysis of the 16S rDNA sequencedata.The results of this study subsequently indicate that the proposal by Vorobjevaet al. (1983) to include P. coccoides as a new species within the genusPropionibacterium is incorrect due to the higher degree of phenetic, molecular andphylogenetic similarity between Luteococcus japonicus and P. coccoides thanbetween the latter and the genus Propionibacterium. It is subsequently proposed thatthe P. coccoides strains be putatively reclassified as Luteococcus japonicussubspecies casei and Luteococcus japonicus subspecies tyrophilus and that the genusdescription of Luteococcus be revised to include the phenetic and moleculardescription of these strains.

[发布机构] University of the Free State