Partial recN gene sequencing: a new tool for identification and phylogeny within the genus Streptococcus

<jats:p>Partial sequences of the<jats:italic>recN</jats:italic>gene (1249 bp), which encodes a recombination and repair protein, were analysed to determine the phylogenetic relationship and identification of streptococci. The partial sequences presented interspecies nucleotide similarity of 56.4–98.2 % and intersubspecies similarity of 89.8–98 %. The mean DNA sequence similarity of<jats:italic>recN</jats:italic>gene sequences (66.6 %) was found to be lower than those of the 16S rRNA gene (94.1 %),<jats:italic>rpoB</jats:italic>(84.6 %),<jats:italic>sodA</jats:italic>(74.8 %),<jats:italic>groEL</jats:italic>(78.1 %) and<jats:italic>gyrB</jats:italic>(73.2 %). Phylogenetically derived trees revealed six statistically supported groups:<jats:italic>Streptococcus salivarius</jats:italic>,<jats:italic>S. equinus</jats:italic>,<jats:italic>S. hyovaginalis</jats:italic>/<jats:italic>S. pluranimalium</jats:italic>/<jats:italic>S. thoraltensis</jats:italic>,<jats:italic>S. pyogenes</jats:italic>,<jats:italic>S. mutans</jats:italic>and<jats:italic>S. suis</jats:italic>. The ‘mitis’ group was not supported by a significant bootstrap value, but three statistically supported subgroups were noted:<jats:italic>Streptococcus sanguinis</jats:italic>/<jats:italic>S. cristatus</jats:italic>/<jats:italic>S. sinensis</jats:italic>,<jats:italic>S. anginosus/S. intermedius/S. constellatus</jats:italic>(the ‘anginosus’ subgroup) and<jats:italic>S. mitis</jats:italic>/<jats:italic>S. infantis</jats:italic>/<jats:italic>S. peroris</jats:italic>/<jats:italic>S. oralis</jats:italic>/<jats:italic>S. oligofermentans</jats:italic>/<jats:italic>S. pneumoniae</jats:italic>/<jats:italic>S. pseudopneumoniae</jats:italic>. The partial<jats:italic>recN</jats:italic>gene sequence comparison highlighted a high percentage of divergence between<jats:italic>Streptococcus dysgalactiae</jats:italic>subsp.<jats:italic>dysgalactiae</jats:italic>and<jats:italic>S. dysgalactiae</jats:italic>subsp.<jats:italic>equisimilis</jats:italic>. This observation is confirmed by other gene sequence comparisons (<jats:italic>groEL</jats:italic>,<jats:italic>gyrB</jats:italic>,<jats:italic>rpoB</jats:italic>and<jats:italic>sodA</jats:italic>). A high percentage of similarity was found between<jats:italic>S. intermedius</jats:italic>and<jats:italic>S. constellatus</jats:italic>after sequence comparison of the<jats:italic>recN</jats:italic>gene. To study the genetic diversity among the ‘anginosus’ subgroup,<jats:italic>recN</jats:italic>,<jats:italic>groEL</jats:italic>,<jats:italic>sodA</jats:italic>,<jats:italic>gyrB</jats:italic>and<jats:italic>rpoB</jats:italic>sequences were determined for 36 clinical isolates. The results that were obtained confirmed the high genetic diversity within this group of streptococci.</jats:p>