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Understanding the molecular mechanism of type-IX secretion in Porphyromonas gingivalis

Project description

Understanding the mechanisms that bacteria use to cause disease is key for the development of new antimicrobial compounds. Many virulence factors of bacteria are proteins (e.g. toxins) secreted directly into their environment or host using dedicated secretion machines. However, many bacteria can also form outer-membrane vesicles (OMVs) via blebbing of their outer membrane, which can be used as a mechanism to export proteins out of the cell. OMVs can diffuse long distances and fuse with other bacteria and hosts, releasing their contents.

Porphyromonas gingivalis is a Gram-negative bacterium of the oral cavity that causes chronic periodontitis. It utilizes a type-IX secretion system (T9SS/PorSS) to export virulence factors across its outer membrane. These are covalently attached to the cell surface but also enriched in OMVs. However, very little is known about how this machine works to export its cargo but also how these proteins are then sorted into OMVs.

In this project you will study how proteins targeted for type IX-dependent secretion are recognized but also what the linksare between their export and OMV biogenesis. This project will involve the use of i) microbiology, ii) molecular biology/cloning, iii) biochemistry/biophysics and iv) structural biology. Proteins of the T9SS will be genetically knocked out and the effects on Porphyromonas gingivalis OMV biogenesis assessed. These proteins will also be cloned, expressed and purified and then characterized with biochemical approaches. Their atomic structures will be determined using X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy.

Funding notes

Applicants wishing to apply for PhD funding through Ciência sem Fronteiras, CONACYT or the China Scholarship Council are welcomed, as are those applicants who can self-fund. For further details on these international funding schemes, go to the relevant funding page.

Applicants should be able to demonstrate that they can cover the cost of living expenses and tuition fees for a minimum of 3.5 years. However, the School does offer a limited number of tuition fee only scholarships for excellent applicants and if you wish to apply for these, you should discuss this with your potential supervisor. Interested candidates should contact Dr Garnett ASAP.


[1] Nakayama, K. (2015) Porphyromonas gingivalis and related bacteria: from colonial pigmentation to the type IX secretion system and gliding motility. J. Periodint. Res. 50: 1-8.

[2] Haurat, M.F., Aduse-Opoku, J., Rangarajan, M., Dorobantu, L., Gray, M.R., Curtis, M.A. & Feldman, M.F. (2011) Selective Sorting of Cargo Proteins into Bacterial Membrane Vesicles. J. Biol. Chem. 286: 1269–1276

[3] Gorasia, D.G., Veith, P.D., Chen, D., Seers, C.A., Mitchell, H.A., Chen, Y-Y., Glew, M.D., Dashper, S.G. & Reynolds, E.c. (2015) Porphyromonas gingivalis Type IX Secretion Substrates Are Cleaved and Modified by a Sortase-Like Mechanism. PLoS Path. 11, e1005152.

[4] Pakharukova, N., Garnett, J.A., Tuittila,M., Paavilainen, S., Diallo, M., Xu, Y., Matthews, S.J. & Zaviolov, A.V. (2015) Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis. PLoS Pathog. 11, e1005269

[5] Garnett, J.A., Martínez-Santos, V.I., Saldaña, Pape, T., Hawthorne, W., Chan, J., Simpson, P., Cota, E., Puente, J.L., Girón, J.A. and Matthews, S. (2012). Structural insights into the biogenesis and biofilm formation by the E. coli common pilus. Proc. Nat. Acad. of Sci. U.S.A. 109, 3950-3955.

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