Real-time visualisation of the intracellular dynamics of Shigella’s virulence plasmid

Bacterial plasmids play critical roles in horizontal gene transfer, antibiotic resistance, virulence, and in shaping the interaction of bacteria with their environment, including those encountered in their hosts. They are integral to bacterial evolution as they act as vectors for rapid genetic change and adaptation. Shigella sonnei is a human-adapted pathogen that is a leading cause of bacillary dysentery and a significant threat to public health. In common to all species of Shigella , S. sonnei harbours an ∼ 210 kb virulence plasmid, pINV, which is essential for its virulence. pINV encodes a Type III secretion system that mediates bacterial invasion of epithelial cells. Understanding the dynamics of replication and segregation of pINV is therefore necessary to define how Shigella retains the plasmid and thence virulence. In this study, we used three fluorescent tagging approaches to detect the presence of pINV in live S . sonnei to allow tracking of the plasmid during cell division. Conclusively, we found that tagging the plasmid with the parS- ParB partitioning system sequences from Caulobacter crescentus chromosome, allowed suitable visualization of the single copy pINV in S. sonnei. This comprehensively enabled us to monitor the location and segregation of the plasmid during bacterial growth.