Branching order of members of the salivarius group as inferred from ML and MP analyses of secY gene sequences (1287 positions; 735 variable, 686 phylogenetically informative). The best ML tree computed with PHYML 3.0 under the GTR+Γ4+I model of nucleotide substitution is shown here. Bootstrap support for the major nodes is indicated over the corresponding nodes: ML values left, MP values right. Asterisks denote nodes that were retrieved in all the bootstrap replicates. Dashes indicate nodes that were retrieved in fewer than 50% of the bootstrap replicates. Streptococcal species belonging to the salivarius group are shown in orange (S. salivarius), blue (S. vestibularis) or green (S. thermophilus). Other streptococcal species shown in black were outgroups. Branch lengths are drawn to scale.