Research article

Evolutionary relationships among salivarius streptococci as inferred from multilocus phylogenies based on 16S rRNA-encoding, recA, secA, and secY gene sequences

Jean-François Pombert¹ , Viridiana Sistek² , Maurice Boissinot² and Michel Frenette³

¹  Canadian Institute for Advanced Research, Evolutionary Biology Program, Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada

²  Centre de Recherche en Infectiologie de l'Université Laval, Centre Hospitalier Universitaire de Québec (Pavilion CHUL), Quebec City, QC, G1V 4G2, Canada

³  Groupe de Recherche en Écologie Buccale, Faculté de Médecine Dentaire, Université Laval, Quebec City, QC, G1V 0A6, Canada

author email corresponding author email

BMC Microbiology 2009, 9:232doi:10.1186/1471-2180-9-232

Published:	30 October 2009

Abstract

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.

Conclusion

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.