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

Abstract

Partial sequences of therecNgene (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 ofrecNgene sequences (66.6 %) was found to be lower than those of the 16S rRNA gene (94.1 %),rpoB(84.6 %),sodA(74.8 %),groEL(78.1 %) andgyrB(73.2 %). Phylogenetically derived trees revealed six statistically supported groups:Streptococcus salivarius,S. equinus,S. hyovaginalis/S. pluranimalium/S. thoraltensis,S. pyogenes,S. mutansandS. suis. The ‘mitis’ group was not supported by a significant bootstrap value, but three statistically supported subgroups were noted:Streptococcus sanguinis/S. cristatus/S. sinensis,S. anginosus/S. intermedius/S. constellatus(the ‘anginosus’ subgroup) andS. mitis/S. infantis/S. peroris/S. oralis/S. oligofermentans/S. pneumoniae/S. pseudopneumoniae. The partialrecNgene sequence comparison highlighted a high percentage of divergence betweenStreptococcus dysgalactiaesubsp.dysgalactiaeandS. dysgalactiaesubsp.equisimilis. This observation is confirmed by other gene sequence comparisons (groEL,gyrB,rpoBandsodA). A high percentage of similarity was found betweenS. intermediusandS. constellatusafter sequence comparison of therecNgene. To study the genetic diversity among the ‘anginosus’ subgroup,recN,groEL,sodA,gyrBandrpoBsequences were determined for 36 clinical isolates. The results that were obtained confirmed the high genetic diversity within this group of streptococci.