Stefan Pukatzki, PhD
Dept. of Medical Microbiology & Immunology
University of Alberta
Faculty of Medicine & Dentistry
T6G 2E1 Edmonton, AB
Ph : (780) 492-0904
Fx : (780) 492-7521
Em : email@example.com
- Associate Professor, Dept. of Medical Microbiology & Immunology
My laboratory studies the interaction between microbial pathogens and their hosts. To cause infections, bacteria use sophisticated strategies, some of which involve virulence factors that interact with cellular components and signaling pathways of host cells. Part of the allure of this area of research is that it not only allows us to observe a cat-and-mouse game of attack and response over evolutionary time, but it also permits us to identify novel drug targets for alternative therapies.
A number of host-pathogen interactions must have evolved in environmental reservoirs where bacteria and eukaryotic predators occupy the same niche. As a consequence, pathogens may apply some of the strategies that they acquired in the environment when exposed to humans. With this concept in mind, we have pioneered the use of the environmental amoeba Dictyostelium discoideum as a genetically accessible host model to discover novel bacterial virulence mechanisms. This approach has lead to the identification of the type VI protein secretion pathway in Vibrio cholerae – the causative agent of cholera. The type VI system confers cytotoxicity not only toward amoebae, but also mammalian macrophages, indicating that the host targets are evolutionarily conserved.
Vibrio cholerae utilizes conserved virulence mechanisms to kill Dictyostelium: We can grow Dictyostelium cells in the laboratory by plating them with avirulent bacteria, like Klebsiella aerogenes. Amoebae ingest bacteria, which enables them to grow and form plaques. When Dictyostelium is plated with virulent Vibrio cholerae, amoebae are killed and unable to form plaques (middle plate). However, when we remove virulence genes from Vibrio, Dictyostelium cells can now utilize these bacteria as a source of nutrients, and form plaques (right plate). We can exploit this phenotypical difference and screen mutant libraries for virulence genes and their host targets.
Our biochemical and genetic data suggest that the type VI system injects effector molecules into the cytosol of infected host cells. We have identified one effector, VgrG1, which crosslinks cytoskeletal actin monomers to injure host cells – a process that requires direct contact. We are currently conducting experiments to define the contribution of each type VI gene to the secretion pathway, characterize the supramolecular structure of the secretion apparatus, and identify host targets of type VI effectors.
Our studies will aid our molecular understanding of how bacteria cause disease, in particular the contribution of VI-mediated toxin secretion.
- Verena Bachmann (Post Doctoral Fellow)
- Ben Kostiuk (Graduate Student)
- Daniel Unterweger (Graduate Student)
- Pukatzki, S.; Ma, A.T.; Sturtevant, D; Krastins, B.; Sarracino, D.; Nelson, W.C.; Heidelberg J.F.; Mekalanos, J.J.: Identification of a conserved protein secretion system in Vibrio cholerae using the Dictyostelium host model system. Proceedings of the National Academy of Sciences 103: 1528-1533. 2006.
- Smith, M.G.; Gianoulis, T.A.; Pukatzki, S.; Mekalanos, J.J.; Ornston, L.N.; Gerstein, M.; Snyder, M.: New insights into Acinetobacter baumannii pathogenesis revealed by high-density pyrosequencing and transposon mutagenesis. Genes & Development 21: 601-614. 2007.
- Lee, V.T.; Pukatzki, S.; Sato, H.; Kikawada, E.; Kazimirova, A.A.; Huang, J.; Li, X.; Arm, J.P.; Frank, D.W.; Lory, S.: Pseudolipasin A Is a Specific Inhibitor for Phospholipase A2 Activity of Pseudomonas aeruginosa Cytotoxin ExoU. Infection & Immunity: 75 (3): 1089-1098. 2007.
- Pukatzki, S.; Kessin, R.H.; Mekalanos, J.J.: The human pathogen Pseudomonas aeruginosa utilizes conserved virulence pathways to infect the social amoeba Dictyostelium discoideum. Proceedings of the National Academy of Sciences 99 (5): 3159-3164. 2002.
For more details you should also have a look at our Pukatzki lab web site.