Functional versatility and host adaptation of the type VI secretion system

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Type VI secretion systems (T6SS) are versatile and dynamic nanomachines that Gram-negative bacteria have adapted for use in numerous different biological functions. These include self-recognition and killing of non-self bacteria, natural competence, and direct communication with eukaryotic cells, such as with mammalian, avian, reptile, and plant hosts. Given the broad functionality of the T6SS, the long-term goal of my proposed research program is to study the amazing versatility of this secretion system to ask the question: how have Gram-negative bacteria adapted the T6SS for various roles and numerous hosts?******The T6SS is used to forcibly inject effector molecules into nearby cells and the encoding genes for the apparatus often found in a distinct locus. However, many species have been shown to have numerous uncharacterized extra open reading frames, or non-core genes, and/or auxiliary gene clusters that are hypothesized to be regulators and effectors of the system. My NSERC proposal addresses the question of T6SS versatility by characterizing non-core genes at the molecular level, both biochemically and structurally.******The model system for this proposal is the Salmonella T6SS because; 1) Salmonella has an extensive host-range (humans, farm-animals, reptiles), 2) the Salmonella T6SS non-core genes differ by serovar and host-species, with many shown to be crucial for proper interaction with a host, and 3) there are a large number of strains, protein expression tools, and genetic tools that are available to work with the system. Given the diversity of the T6SS across Salmonella spp. this research will lay the ground-work for the comparison of Salmonella and expansion to other Gram-negative species.******This research program will begin by focusing on four non-core gene clusters of the Salmonella typhimurium T6SS (total of 12 genes of interest), with the working hypothesis that they provide the T6SS with its amazing versatility. Genetic studies have shown these to be crucial for survival within macrophages and potentially aid in competition with the gut microbiota. However, there is a lack of a mechanistic understanding of the corresponding proteins, making it unclear if they are effectors that manipulate target cells, regulators of the T6SS apparatus, or if they are bonafide determinants of host-cell specificity. Together with my trainees, we aim to determine their molecular structures as a guide to explore their function, and in parallel discover protein interaction partners either in Salmonella or the host organism. As a consequence, the combined structural and biochemical data will reveal how the Salmonella typhimurium T6SS has been adapted for its specific role(s). These studies will involve a combination of molecular biology, structural biology and protein biochemistry and will provide a multidisciplinary training environment for students to pursue careers in research and the life sciences.