Investigation of the role of Treponema denticola motility and uncharacterized protein TDE0659 in synergistic biofilm formation with Porphyromonas gingivalis
AuthorNg, Hong Min
AffiliationMelbourne Dental School
Document TypePhD thesis
Access StatusThis item is embargoed and will be available on 2020-11-28. This item is currently available to University of Melbourne staff and students only, login required.
© 2018 Dr. Hong Min Ng
Chronic periodontitis has a polymicrobial biofilm etiology and interactions between key oral bacterial species such as Porphyromonas gingivalis, Treponema denticola and Tannerella forsythia contribute to disease progression. P. gingivalis and T. denticola both have a set of virulence factors that are believed to contribute to the initiation and development of disease. It has been previously shown that P. gingivalis and T. denticola exhibit strong synergy in growth, biofilm formation and virulence in an animal model of disease. The motility of T. denticola, although not considered as a classic virulence factor, is likely to be involved in synergistic biofilm development between P. gingivalis and T. denticola. In order to investigate this, an optimized protocol for the transformation of T. denticola was developed and used to produce a number of T. denticola mutants targeting the motility machinery. The resulting mutants lacked periplasmic flagella (∆flgE) or possessed periplasmic flagella that were either non-functional (∆motA and ∆motB) or non-regulatable (∆cheY). ∆cheY contained a large genomic excision and was thus omitted from the study, however analyses of ∆flgE, ∆motA and ∆motB showed that they were impaired in motility and growth. Quantitative proteomic analyses of mutant strains showed that the inactivation of these motility-associated genes, especially motA and motB, have far reaching effects beyond motility. The inactivation of motA and motB activated a cellular stress response in the mutants and directly or indirectly impacted the growth of the mutants through the change in abundance of a number of proteins. T. denticola motility mutant and WT strains were grown as mono- and dual-species biofilms with P. gingivalis. Results showed that T. denticola motility and/or spiral morphology are required for monospecies biofilm formation and T. denticola periplasmic flagella are essential for synergistic biofilm formation with P. gingivalis. Zones of clearing were observed between T. denticola sibling colonies grown close to one another on agar, similar to the sibling killing phenomenon observed in Paenibacillus dendritiformis. Given that a sibling killing phenomenon could have a considerable effect on biofilm formation, this phenomenon was investigated further in T. denticola. Although T. denticola was found to possess a homologue (TDE0659) of the dendritiformis sibling bacteriocin (DfsB) produced by P. dendritiformis, the protein did not undertake the same function in T. denticola. Construction and analysis of a T. denticola mutant strain lacking TDE0659 showed that the loss of this gene product from T. denticola did not prevent adjacent sibling colonies from forming zones of clearing on agar, further the mutant was able to form monospecies biofilms similar to WT. However, the lack of TDE0659 prevented the incorporation of P. gingivalis in a dual-species static biofilm with T. denticola, indicating that TDE0659 is essential for promoting synergistic biofilm formation with P. gingivalis. Together, the findings from this study will further our understanding about how P. gingivalis and T. denticola interact with one another and proliferate during disease.
KeywordsTreponema denticola; Porphyromonas gingivalis; synergistic polymicrobial biofilm; motility; T. denticola dendritiformis sibling bacteriocin
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