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Modulation of epigenetic phase variations in periodontal bacteria as a novel strategy for control of periodontal disease

Project Description

Rationale and overall aim of the project: Periodontal disease (PD) is a major health issue in Scotland and worldwide with ever-increasing prevalence due to the increasing age of the population. The inflammatory process leading to progressive destruction of tooth-supporting structures in PD is driven by complex bacteria in conjunction with abnormal immune responses. All bacterial species implicated in PD colonise the mouth of healthy individuals and the mere presence of these species does not promote disease. The overall bacterial mechanisms which mediate the transition from harmless bacteria to opportunistic pathogens in PD are unknown. This project will characterise an important biological phenomenon that has been completely ignored in periodontal bacteria, namely the phase variations of clonal bacterial populations and their role in disease initiation and progression. In some bacteria it has been shown that the “switching” to a pathogenic status is genetically unstable and that epigenetic phase variations which determine distinct degrees of pathogenicity are controlled by rearrangement of genes contained in a type I restriction-modification (R-M) system 1. A recent genomic study indicate that these systems exist in most major periodontal bacteria 2. The aim of this project is to characterise the phase variations associated with rearrangements of R-M systems in periodontal bacteria and to study the resulting microbiological changes and effect on ability to cause disease.

Methods: Phase variation in R-M loci will be monitored using combined PCR/restriction genescan analysis. Phenotypic behaviour of variant clones will be tested using a range of methodologies including growth assays, biofilm formation, adhesion/invasion of gingival epithelial cells and inhibition of IL-8 production. The molecular characterisation of strains will include full genome sequencing, methylome analysis and gene expression profiling by RNAseq.

Milestone 1. Identification of one prototypic strain of one of the four species with clear evidence of phenotypic changes induced by the phase variable methylation system.
Milestone 2. Description of methylation profiles and changes in gene expression associated with phase variation.

Translational aspect: The project has the potential of unveiling an epigenetic mechanism which controls overall changes of phenotypic behavior of periodontal bacteria leading to destruction of tooth supporting structures, and addresses a critical gap to understanding pathogenicity mechanisms of periodontal pathogens. It is expected to drive a novel approach to targeting oral opportunistic pathogens, namely the modulation of the activity of R-M systems as opposed to targeting putative virulence factors or specific strains.
Findings will ultimately contribute to the imperative of developing targeted antimicrobial approaches for control of PD as an alternative to broad-spectrum antimicrobial therapy (associated with bacterial resistance to antimicrobials) and a complement to mechanical and local measures (heavily reliant on patient compliance).

This project is advertised in relation to the research areas of DENTAL SCIENCES. Formal applications can be completed online: You should apply for Degree of Doctor of Philosophy in Dental Sciences, to ensure that your application is passed to the correct person for processing.

NOTE CLEARLY THE NAME OF THE SUPERVISOR AND EXACT PROJECT TITLE ON THE APPLICATION FORM. Applicants are limited to applying for a maximum of 3 applications for funded projects. Any further applications received will be automatically withdrawn.

Funding Notes

This project is funded by a University of Aberdeen Elphinstone Scholarship. An Elphinstone Scholarship covers the cost of tuition fees only, whether home, EU or overseas.

For details of fees: View Website

Candidates should have (or expect to achieve) a minimum of a First Class Honours degree in a relevant subject. Applicants with a minimum of a 2:1 Honours degree may be considered provided they have a Distinction at Masters level.


1. Manso et al. A random six-phase switch regulates pneumococcal virulence via global epigenetic changes. Nature Communication 2014 Sep 30;5:5055.

2. Haigh RD, Crawford L, Ralph J, Wanford JJ, Vartoukian SR, Hijazi K, Wade W and Oggioni MRO. Phase variable restriction modification systems in periodontal pathogens Prevotella intermedia, Tannerella forsythia and Porphyromonas gingivalis. Genome Announc 2017 Nov 16;5(46).

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