Porphyromonas gingivalis Uses Specific Domain Rearrangements and Allelic Exchange to Generate Diversity in Surface Virulence Factors

Abstract

Porphyromonas gingivalis is a keystone pathogen of chronic periodontitis. The virulence of P. gingivalis is reported to be strain related and there are currently a number of strain typing schemes based on variation in capsular polysaccharide, the major and minor fimbriae and adhesin domains of Lys-gingipain (Kgp), amongst other surface proteins. P. gingivalis can exchange chromosomal DNA between strains by natural competence and conjugation. The aim of this study was to determine the genetic variability of P. gingivalis strains sourced from international locations over a 25-year period and to determine if variability in surface virulence factors has a phylogenetic basis. Whole genome sequencing was performed on 13 strains and comparison made to 10 previously sequenced strains. A single nucleotide polymorphism-based phylogenetic analysis demonstrated a shallow tri-lobed phylogeny. There was a high level of reticulation in the phylogenetic network, demonstrating extensive horizontal gene transfer between the strains. Two highly conserved variants of the catalytic domain of the major virulence factor the Kgp proteinase (KgpcatI and KgpcatII) were found. There were three variants of the fourth Kgp C-terminal cleaved adhesin domain. Specific variants of the cell surface proteins FimA, FimCDE, MfaI, RagAB, Tpr, and PrtT were also identified. The occurrence of all these variants in the P. gingivalis strains formed a mosaic that was not related to the SNP-based phylogeny. In conclusion P. gingivalis uses domain rearrangements and genetic exchange to generate diversity in specific surface virulence factors.

Porphyromonas gingivalis as a Possible Risk Factor in the Development/Severity of Acute Alcoholic Hepatitis

“…Strain 33277 represents the fimbriated/nonencapsulated lineage and possesses both the Mfa1 and FimA fimbriae, which are present in 20 of 21 P. gingivalis strains. Strain W83 represents the nonfimbriated/capsulated lineage . Both strains are pathogenic in animal models of infection .…”

“…Strain W83 represents the nonfimbriated/capsulated lineage. (32) Both strains are pathogenic in animal models of infection. (33) Detection of the antibodies showed a wide range of concentrations.…”

Genetic exchange and reassignment in Porphyromonas gingivalis

“…P. gingivalis exchanges chromosomal DNA between strains by natural competence and conjugation [6–8]. By using antibiotic resistance markers, it was demonstrated that the strains ATCC 33277 T and W83 of P. gingivalis were able to exchange chromosomal DNA resulting in offspring, which carried DNA from both donor and recipient [6].…”

“…A high level of reticulation was seen in the phylogenetic networks constituted by 23 strains of P. gingivalis [8]. This indicated extensive horizontal gene transfer between the strains.…”

“…IS transposition can be limited by CRISPR interference as CRISPR limits both IS transposition and the introduction of DNA from other P. gingivalis cells [51]. Thus specific domain rearrangements and genetic exchange to generate diversity in surface virulence factors [8] cannot alone be held responsible for the diversity in virulence, although they probably play an important role.…”