Evolutionary relationships among salivarius streptococci as inferred from multilocus phylogenies based on 16S rRNA-encoding, recA, secA, and secY gene sequences.
BACKGROUND
Streptococci are divided into six phylogenetic groups, i.e, anginosus, bovis, mitis, mutans, pyogenic, and salivarius, with the salivarius group consisting of only three distinct species. Two of these species, Streptococcus salivarius and Streptococcus vestibularis, are members of the normal human oral microflora whereas the third, Streptococcus thermophilus, is found in bovine milk. Given that S. salivarius and S. vestibularis share several physiological characteristics, in addition to inhabiting the same ecosystem, one would assume that they would be more closely related to each other than to S. thermophilus. However, the few phylogenetic trees published so far suggest that S. vestibularis is more closely related to S. thermophilus. To determine whether this phylogenetic relationship is genuine, we performed phylogenetic inferences derived from secA and secY, the general secretion housekeeping genes, recA, a gene from a separate genetic locus that encodes a major component of the homologous recombinational apparatus, and 16S rRNA-encoding gene sequences using other streptococcal species as outgroups.


RESULTS
The maximum likelihood (ML) and maximum parsimony (MP) phylogenetic inferences derived from the secA and recA gene sequences provided strong support for the S. vestibularis/S. thermophilus sister-relationship, whereas 16S rRNA-encoding and secY-based analyses could not discriminate between alternate topologies. Phylogenetic analyses derived from the concatenation of these sequences unambiguously supported the close affiliation of S. vestibularis and S. thermophilus.


CONCLUSIONS
Our results corroborated the sister-relationship between S. vestibularis and S. thermophilus and the concomitant early divergence of S. salivarius at the base of the salivarius lineage.
Pombert
Jean-François
JF
Groupe de Recherche en Ecologie Buccale, Faculté de Médecine Dentaire, Université Laval, Quebec City, QC G1V 0A6, Canada. jpombert@interchange.ubc.ca
Sistek
Viridiana
V
Boissinot
Maurice
M
Frenette
Michel
M
D000251:Adenosine Triphosphatases / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D019143:Evolution, Molecular; D026901:Membrane Transport Proteins / Q000235:genetics; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics*; D011938:Rec A Recombinases / Q000235:genetics; D000069816:SEC Translocation Channels; D000081416:SecA Proteins; D017422:Sequence Analysis, DNA; D013291:Streptococcus / Q000145:classification / Q000235:genetics*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D012336:RNA, Ribosomal, 16S; D000069816:SEC Translocation Channels; D011938:Rec A Recombinases; D000251:Adenosine Triphosphatases; D000081416:SecA Proteins