Fig. 1

The modular structure of the T7SS loci of S. aureus. Schematic representation of the ess operon in four reference genomes strains of S. aureus, demonstrating the four modules that describe variation in the operon and the four major variants of essC and its immediate downstream gene cluster: Module 1. A conserved cluster of five genes (esxA to essB) at the 5’ end of the operon that encode one secreted protein (EsxA) and other components of the T7SS machinery; Module 2. A variable region that includes the essC gene, of which there are four variants, each associated with a distinct cluster of four to six downstream genes that are predicted to encode a number of secreted and transmembrane proteins; Module 3. A highly variable region which encodes a number of predicted transmembrane proteins and proteins possessing the domain of unknown function (DUF600); and Module 4. A 3’ conserved region, encoding two highly conserved hypothetical proteins of unknown function. Light pink shading demonstrates regions that are conserved between isolates, with the degree of amino acid identity between isolates displayed in red text. An asterisk above the gene indicates that it is present as a pseudogene