Investigating the molecular mechanism of effector secretion by the bacterial type IV secretion system

This joint PhD project will be based at The University of Melbourne with a minimum 12 month stay at the Shanghai Jiao Tong University.

Project description

The bacterial type IV secretion system (T4SS) translocates DNA-protein complexes, peptidoglycan and a wide range of effectors proteins into target cells and is responsible for multiple disease conditions in humans. However, the structural basis of T4SS function remains poorly understood. Recently, using electron cryotomography (cryoET), we revealed the first in situ architecture of the L. pneumophila Dot/Icm T4SS (Ghosal et al, 2019a). Driven by our common interest in bacterial secretion systems and complementary expertise, in this collaborative effort with Tao Dong’s laboratory at SJTU, we propose to resolve the structural and mechanistic details of effector secretion by the bacterial T4SS.

Tao Dong’s laboratory at SJTU is using advanced tools in bacterial genetics and microbiology to reveal the molecular details of bacterial type VI secretion system assembly and function. Encouraged by our mutual interest in bacterial secretion systems, common goal and complementary expertise, we aim to address some of the outstanding questions in the bacterial T4SS field.

We will use hybrid methods including in situ structural biology, correlative light and electron microscopy (CLEM), bacterial genetics, biochemistry and optical imaging to address the following questions:

  1. What triggers gate opening or activates of the T4SS?
  2. What are the structural changes associated with the activation of this complex? And finally;
  3. How effectors are secreted through the T4SS channel with a tight spatiotemporal control?

At the SJTU, the Dong lab has a strong track record in bacterial genetics and in microbiology (Liang et al., 2015, PNAS; Burkinshaw et al., 2018, Nature Microbiology; Pei et al., 2020, Nature Communications), whereas the Ghosal lab has been using cryoET and structural biology methods to reveal structural details of bacterial secretion systems (Ghosal et al., 2019 Nature Microbiology; Ghosal et al., 2019b Nature Microbiology). As per our expertise, the Ghosal lab will lead the structural aspects of this project, while the Dong lab will perform all the bacterial genetics and fluorescence imaging experiments. Together, as a team, we hope to substantially contribute towards our understanding of how the T4SS functions. Students participating in this UofM and SJTU joint program will receive training from both the laboratories and will have a unique international research experience.



  1. Ghosal, D., Jeong, K.C., Chang, Y.-W., Gyore, J., Teng, L., Gardner, A., Vogel, J.P., and Jensen, G.J.  (2019a). Molecular architecture, polar targeting and biogenesis of the Legionella Dot/Icm T4SS. Nat. Microbiol. 4, 1173–1182.
  2. Amyot, MW., deJesus, D., Isberg RI (2013). Poison domains block transit of translocated substrates via the Legionella pneumophila Icm/Dot system. Infect Immun. 2013 Sep;81(9):3239-52
  3. Liang, X., Kamal, F., Pei, T.-T., Xu, P., Mekalanos, J.J., and Dong, T.G. (2019). An onboard checking mechanism ensures effector delivery of the type VI secretion system in Vibrio cholerae. Proc. Natl. Acad. Sci. 116, 23292–23298.
  4. Burkinshaw, B.J., Liang, X., Wong, M., Le, A.N.H., Lam, L., and Dong, T.G. (2018). A type VI secretion system effector delivery mechanism dependent on PAAR and a chaperone–co-chaperone complex. Nat. Microbiol. 3, 632– 640.
  5. Pei, T.-T., …, Dong, T.G. (2020). Intramolecular chaperone-mediated secretion of an Rhs effector toxin by a type VI secretion system. Nat. Commun. 11, 1865.
  6. Ghosal, D., Kim, K.W., Zheng, H., Kaplan, M., Truchan, H.K., Lopez, A.E., McIntire, I.E., Vogel, J.P., Cianciotto, N.P., and Jensen, G.J. (2019b). In vivo structure of the Legionella type II secretion system by electron cryotomography. Nat. Microbiol. 4, 2101–2108.
  7. Liang, X., Moore, R., Wilton, M., Wong, M.J.Q., Lam, L., and Dong, T.G. (2015). Identification of divergent type VI secretion effectors using a conserved chaperone domain. Proc. Natl. Acad. Sci. 112, 9106–9111.

The project will be complemented by the project on Structure and function of the type VI secretion system in bacterial pathogens and the collaboration will ensure a successful completion of the project.

Supervision team:

Dr Debnath Ghosal (The University of Melbourne)

Professor Tao Dong (Shanghai Jiao Tong University)

How to apply