IADR Abstract Archives
Porphyromonas gingivalis Surface Protein Variability is not Related to Phylogeny
Objectives: Porphyromonas gingivalis is regarded as a keystone pathogen of chronic periodontitis. The virulence of P. gingivalis is reported to be strain related. P. gingivalis can exchange chromosomal DNA between strains by natural competence and conjugation. The aim of this study was to determine the genetic variability P. gingivalis strains and determine if variability in virulence related proteins has a phylogenetic basis.
Methods: Whole genome sequencing was performed on thirteen strains and comparison made to ten previously sequenced strains.
Results: A single nucleotide polymorphism-based phylogenetic analysis demonstrated a shallow tri-lobed phylogeny indicating low phylogenetic diversity. The P. gingivalis pan-genome consisted of 3920 clusters, containing 1326 core gene families present in all 21 strains, 1427 gene families that were found in more than one strain and 1167 strain-specific gene families. The core genome comprised 72% of the average P. gingivalis genome of 1832 predicted CDSs. There was a high level of reticulation in the phylogenetic network, demonstrating extensive horizontal gene transfer between the strains. Two distinct forms of the Kgp protease catalytic domain were found, along with extensive rearrangement of the Kgp adhesin domains. Four distinct types of FimA were detected and there were two major forms of the fimCDE gene cluster. There were two major forms of MfaI, four discernible types of RagAB, two variants of Streptopain and three of Tpr. A comparison of the occurrence of all these protein variants in the P. gingivalis strains formed a mosaic that was not related to the phylogeny. The variability in these eight proteins alone generated nearly 7000 different combinations and none of the P. gingivalis strains in this study had the same combination of variants of these proteins.
Conclusions: In conclusion P. gingivalis uses specific domain rearrangements and allelic exchange through horizontal gene transfer to generate diversity in specific surface proteins.
Methods: Whole genome sequencing was performed on thirteen strains and comparison made to ten previously sequenced strains.
Results: A single nucleotide polymorphism-based phylogenetic analysis demonstrated a shallow tri-lobed phylogeny indicating low phylogenetic diversity. The P. gingivalis pan-genome consisted of 3920 clusters, containing 1326 core gene families present in all 21 strains, 1427 gene families that were found in more than one strain and 1167 strain-specific gene families. The core genome comprised 72% of the average P. gingivalis genome of 1832 predicted CDSs. There was a high level of reticulation in the phylogenetic network, demonstrating extensive horizontal gene transfer between the strains. Two distinct forms of the Kgp protease catalytic domain were found, along with extensive rearrangement of the Kgp adhesin domains. Four distinct types of FimA were detected and there were two major forms of the fimCDE gene cluster. There were two major forms of MfaI, four discernible types of RagAB, two variants of Streptopain and three of Tpr. A comparison of the occurrence of all these protein variants in the P. gingivalis strains formed a mosaic that was not related to the phylogeny. The variability in these eight proteins alone generated nearly 7000 different combinations and none of the P. gingivalis strains in this study had the same combination of variants of these proteins.
Conclusions: In conclusion P. gingivalis uses specific domain rearrangements and allelic exchange through horizontal gene transfer to generate diversity in specific surface proteins.