Genome-wide screen identifies novel factors for surface protein cross-wall trafficking and cell envelope homeostasis in Staphylococcus aureus

ABSTRACT Cell-wall-anchored surface proteins are integral components of gram-positive bacterial cell envelopes. The trafficking of many surface proteins carrying a YSIRK/G-S signal peptide is synchronized with cell envelope biogenesis during cell division, whereby YSIRK proteins traffic to the septal membrane and anchor to the septal peptidoglycan (cross-wall). Previous work demonstrated that LtaS-mediated lipoteichoic acid (LTA) synthesis restricts YSIRK proteins’ septal trafficking. Here, we did a comprehensive immunofluorescence microscopy screen of the entire Staphylococcus aureus Nebraska Transposon Mutant Library (NTML) for additional factors regulating cross-wall trafficking of staphylococcal protein A (SpA), an archetype of YSIRK proteins. We characterized nine major hits that drastically diminished SpA cross-wall localization, including ypfP, ltaA, mprF, lcpB, lytH, scdA, yjbH, cbiO, and SAUSA300₂311, along with a tagO mutant. Interestingly, unlike the ltaS mutant that delocalizes SpA at both the septal membrane and peptidoglycan layer, all the hits only delocalized SpA at the peptidoglycan layer, suggesting that these mutants affect the late-stage SpA trafficking. In addition, mutants of lcpB, yjbH, cbiO, and 2311 exhibited both transcriptional and spatial regulations. All the hits showed defects in cell cycle, cell morphology, and spatially dysregulated peptidoglycan (PG) synthesis. The shared phenotypes among the mutants suggest that impaired PG homeostasis and cell cycle defects are the mechanisms underlying dysregulated SpA localization. Overall, this work not only expands our understanding of YSIRK protein cross-wall trafficking but also identifies new leads that have a broader impact on the dynamics of cell cycle and cell envelope homeostasis. IMPORTANCE Surface proteins of gram-positive bacteria are key virulence factors in the human pathogen Staphylococcus aureus. Most surface proteins carry a YSIRK/G-S type signal peptide that promotes cross-wall trafficking and attachment to the septal cell wall during cell division. This study identified several new factors regulating this process through a comprehensive screen. The mutants identified here display dysregulated cell wall synthesis along with cell cycle defects. The results provide new insight into virulence factor trafficking and cell envelope homeostasis, which lays the foundation for developing new drug targets.