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

Laboratoire de Bacteriologie, Hopital de la Timone

¹ E-mail: vroux91{at}live.fr

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