Plasmid biology in human adapted pathogens

Plasmids are responsible for virulence and antimicrobial resistance in many bacteria. We will dissect fundamental mechanisms of plasmid maintenance in the obligate human pathogens, Shigella spp. and Neisseria gonorrhoeae, declared as high priority organisms by WHO/CDC. Toxin:antitoxin (TA) systems (addiction systems) are important for plasmid maintenance by eliminating bacteria failing to inherit a plasmid after cell division. For example, the VapBC TA system is essential for maintaining the 210kb Shigella virulence plasmid. Additionally, TA systems (including VapBC) are increasingly recognised for their role in antibiotic tolerance, often a precursor to resistance. Despite this, little is known of how plasmid maintenance is integrated with the bacterial host, and how TA systems are activated after plasmid loss/during tolerance. Combining our understanding of variation in VapBC and the VapC toxin target tRNAfMet with multidisciplinary approaches (mutagenesis/structural:function studies/single cell analysis), we will define mechanisms of TA system activation and the temporal dynamics of events following plasmid loss that culminate in cell death. We will examine the acquisition and maintenance of resistance plasmids in Shigella and N. gonorrhoeae, and the interactions between plasmids and their contribtion to tolerance and horizontal transfer.