The elucidation of more specific disease associations is presently hampered by the lack of a reliable method for strain identification, and a very poor understanding of how strains differ at the genetic level. Here, we utilized a seven protein-coding gene multilocus sequence analysis (MLSA) approach, to characterize genomic diversity and evolutionary relationships in a small, but
carefully-selected collection of T. denticola isolates of diverse geographical origin. Our results revealed that there are relatively high levels of genetic diversity see more amongst T. denticola strains; with gene sequence similarities ranging between ca. 84 − 100% between the strains. These levels are considerably Androgen Receptor Antagonist in vivo higher than in T. pallidum; where strains of the pallidum and pertenue subspecies share ca. 100-99.6% genome sequence identity, and genetic differences are largely confined to recombination ‘hotspots’ or other areas of acquired DNA sequence . Whilst there were variations in the relative proportions of polymorphic sites present in the seven protein-encoding genes selected for analysis, all were under a strong (purifying) evolutionary pressure to conserve function. We found no evidence of genetic recombination in any gene sequence analyzed, indicating that genes had selleck kinase inhibitor evolved as intact units in each strain. It is interesting to note that the flaA gene, which encodes an endoflagellar
sheath protein that is a known a cell surface-exposed epitope , appeared to follow a similar evolutionary pathway as the pyrH and recA ‘housekeeping’ genes analyzed. Although we also sequenced the 16S rRNA (rrsA/rrsB) gene(s) from each strain, we did not add this to the concatenated multi-gene sequence for phylogenetic analysis. This was because it is present in two identical copies on the T. denticola genome , and may be
under distinct evolutionary Orotidine 5′-phosphate decarboxylase pressures, due to the fact that is not translated into a protein; e.g. it may have increased levels of nucleotide insertions or deletions (indels), or may have selection biases relating to its secondary structure . Based on the concatenated 7-gene (flaA, recA, pyrH, ppnK, dnaN, era and radC) datasets, both the Bayesian (BA) and maximum likelihood (ML) topologies clearly indicated that all 20 T. denticola strains are monophyletic; i.e. they originated from a single common ancestor that was genetically distinct from T. vincentii and T. pallidum (see Figure 3). Our data also indicates that at the genetic level, T. denticola is more closely related to the oral treponeme T. vincentii, than the syphilis spirochete. Six well-defined clades (I-VI) were formed in both the BA and ML trees, which comprised 18 of the 20 strains analyzed. The OTK strain from the USA does not fall within any of the defined clades, possibly due to the relatively low sample size.