Characterisation of a plasmid segregational stability determinant, par, of the staphylococcal multiresistance plasmid, pSK1

Abstract

Staphylococcus aureus is a bacterium that is a common cause of hospital-acquired infections that is also becoming a significant cause of serious community-acquired infections. Many clinical strains of S. aureus carry extrachromosomal DNA elements called plasmids, which often encode genes conferring antimicrobial resistance. Plasmid segregation mechanisms such as active partitioning systems ensure that low copy-number plasmids are accurately segregated and inherited by progeny cells upon division, even in the absence of selection. The staphylococcal multiresistance plasmid, pSK1, contains a gene, par, which enhances the efficiency of plasmid inheritance, possibly via an active plasmid partitioning system. Active plasmid partitioning systems characterised thus far encode two individual proteins – a DNA-binding protein and a force-generating NTPase protein. Although the pSK1 par system is widespread among non-conjugative staphylococcal plasmids, it differs from characterised plasmid partitioning systems by encoding only a single protein, Par. Previous studies have shown that pSK1 Par exhibits both DNA-binding and multimerisation activities that are common to characterised partitioning proteins. Much remains to be elucidated about the mechanism by which pSK1 par facilitates efficient plasmid inheritance. This knowledge gap will be addressed by this experiments described in this thesis, which aim to 1) determine the functional significance the predicted Par domains, particularly the disordered C-terminal domain, 2) identify any host factors that interact with Par, and 3) determine the localisation of Par and plasmid DNA during plasmid segregation in S. aureus. These experiments are designed to provide a broader understanding of the mechanism of par-mediated plasmid inheritance, and provide greater insight into possible methods of disrupting the spread and maintenance of antimicrobial resistance plasmids.