Proteomic analysis of the differential virulence and tropism of Salmonella serovars in food-producing animals
Salmonella enterica is a zoonotic and facultative intracellular pathogen of worldwide importance. Infections present in a variety of ways from asymptomatic colonisation to inflammatory diarrhoea or typhoid fever depending on serovar- and host-specific factors. Human diarrhoeal infections are commonly acquired via the food chain and farm environment owing to the ability of selected non-typhoidal serovars to colonise the intestines of food-producing animals and contaminate the avian reproductive tract and egg. Colonisation of reservoir hosts often occurs in the absence of clinical symptoms, however some S. enterica serovars pose a threat to animal health owing to their ability to cause acute enteritis or translocate from the intestines to other organs causing fever, septicaemia and abortion. Despite the availability of complete genome sequences of isolates representing multiple serovars, the molecular mechanisms underlying Salmonella colonisation, pathogenesis and transmission in reservoir hosts remain ill-defined.
This project will utilise proteomics to characterise the repertoire of secreted proteins from Salmonella serovars differing in virulence and host tropism in food-producing animals, specifically chickens, pigs and cattle. In the first instance, we will define the repertoire of secreted proteins of four genome-sequenced strains of highly-defined differential virulence in food-producing animals. A wealth of literature supports roles for Type 3 secreted effector proteins in Salmonella virulence and some differences in the repertoire and expression level of effectors has been detected between serovars, but with ill-defined consequences. Type 3 secretion systems act in a manner akin to molecular syringes to deliver effectors into target cells where they subvert cellular processes to the benefit of the pathogen. Quantitative proteomics will be used to derive comprehensive data on the repertoire and levels of secreted proteins for all strains tested and a subset of differentially secreted proteins targeted for mutagenesis and analysis in cell- and Galleria-based assays and, where justified, animal models of salmonellosis. We will also map the effector repertoire using T3SS null or dysregulated mutants, as we recently described for pathogenic Burkholderia [Mol Cell Proteomics (2015) 14:905-16]. Wild-type, isogenic mutant and complemented strains will be assessed for uptake and intracellular net replication in primary macrophages differentiated from bone marrow of chickens, pigs and cow using established methods. In addition, the function of novel secreted proteins will be characterised using assays for protein-protein interactions and biochemical activity as appropriate. Where justified, scope exists to evaluate the role of selected factors in target animal models of Salmonella persistence and pathogenesis.
The project will yield valuable information on the molecular basis of tropism and virulence of S. enterica serovars associated with farmed animals. This may, with further development, aid in the development of tools to assess the zoonotic and pathogenic potential of serovars found in farmed animals. Importantly, cross-protective vaccines for control of Salmonella in farmed animals are lacking and the project may identify important conserved antigens for future development.
The student will be registered with the University of Edinburgh and be located at The Roslin Institute. Opportunities will be provided for postgraduate training and travel to relevant national and international conferences. The student will join a vibrant research environment and contribute to high-impact research on the molecular basis of microbial pathogenicity. The project will instil training in diverse areas including computational analysis of genomes, proteomics approaches, molecular methods to manipulate the organism, and cell-based and in vivo assays.
Candidates should have or expect to have a minimum of an appropriate upper 2nd class degree. To qualify for full funding students must be UK or EU citizens who have been resident in the UK for 3 years prior to commencement.
Applications including full CV with names and addresses (including email addresses) of two academic referees, should be sent to: Liz Archibald, Postgraduate Research Student Administration, The Roslin Institute and R(D)SVS, The University of Edinburgh, Easter Bush, Midlothian, EH25 9RG. Or to [Email Address Removed]. When applying please state clearly the title of the studentship and the supervisors in your covering letter.