Evolution of Streptococcus pneumoniae and Its Close Commensal Relatives
Figure 1
Phylogenetic tree constructed with the minimum evolution algorithm in MEGA version 4.0 and based on concatenated partial sequences of the house-keeping enzyme genes ddl, gdh, rpoB, and sodA.
Type strains of individual species are shown with species designation. Bootstrap values (%) are based on 1000 replications. The three major clusters supported by significant bootstrap values are the pneumoniae-mitis-pseudopneumoniae cluster (red lines), the Oralis cluster (blue lines), and the Infantis cluster (green lines). The subcluster of S. pneumoniae strains within the pneumoniae-mitis-pseudopneumoniae cluster is indicated by dark red lines (ruby), S. pseudoneumoniae strains within the pneumoniae-mitis-pseudopneumoniae cluster are indicated by pink, and strains previously assigned to “S. mitis biovar 2” within the Oralis cluster are indicated by dark blue lines. The random presence of homologues of virulence factors usually associated with S. pneumoniae (cap locus, capsule synthesis operon; iga, IgA1 protease gene; lytA, autolysin gene; ply, pneumolysin gene) in the diverse population of Mitis lineages is illustrated. A red signature indicates presence of the virulence gene, and black signature indicates a PCR product size compatible with absence of the gene. Black squares with a red center indicate IgA1 protease activity but an amplicon size in support of lack of an iga gene in the context found in S. pneumoniae. No signature indicates lack of a PCR product presumably due to no match of the primers. The arrow indicates the hypothetical immediate common ancestor of the red cluster. The scale bar refers to genetic divergence as calculated by the MEGA software.