Phylogenetic relationships between diverse strains of Treponema denticola

Abstract

The presence and abundance of the oral spirochete bacterium Treponema denticola have previously been associated with the incidence and severity of periodontal disease. To date, more than 100 different reference strains and clinical isolates of T. denticola have been studied. However, the genetic relationships between these various T. denticola strains have never been systematically investigated. Objectives: To establish the genetic diversity and relationships between 16 of the most highly studied reference strains and clinical isolates of T. denticola using multiple gene sequence analyses. Methods: Sixteen T. denticola strains previously isolated from 3 different continents were selected for genetic analysis. The 16S rRNA gene and six protein-encoding genes highly conserved within bacteria were PCR-amplified from each strain using conserved primer sets. PCR-amplified genes were TOPO-cloned then sequenced. Various software tools were used to analyze sequence data and gene phylogeny.Results: There was significant genetic diversity within the 16 strains analyzed. Several strains isolated from different continents appeared to be very closely related, and we could not identify any geographical relationships. No one gene had sufficient discriminatory power to unambiguously identify or differentiate between the 16 strains, although this could be achieved using the sequences of two genes. Different genes exhibited quite distinct phylogenetic patterns, indicating significant genome plasticity and inter-strain genetic reassortment. Conclusions: Phylogenetic analysis has revealed that there is considerable genetic diversity within the species Treponema denticola. Our results establish a robust and powerful genetic framework for the future analysis and discrimination of T. denticola isolates.