Phenotypic heterogeneity and temporal expression of the capsular polysaccharide in Staphylococcus aureus

• Published in: Molecular microbiology Vol. 98; no. 6; pp. 1073 - 1088
• Main Authors: George, Shilpa E., Nguyen, Tran, Geiger, Tobias, Weidenmaier, Christopher, Lee, Jean C., Liese, Jan, Wolz, Christiane
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.12.2015
• Subjects: Bacterial Capsules - chemistry; Bacterial Capsules - genetics; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biosynthesis; Gene expression; Gene Expression Regulation, Bacterial; Genotype & phenotype; Gram-positive bacteria; Humans; Microbiology; Nose - microbiology; Phenotype; Polysaccharides, Bacterial - biosynthesis; Polysaccharides, Bacterial - genetics; Promoter Regions, Genetic; Proteins; Quorum Sensing; Repressor Proteins - genetics; RNA, Bacterial - genetics; Staphylococcal Infections - microbiology; Staphylococcus aureus - genetics; Staphylococcus aureus - growth & development; Staphylococcus aureus - metabolism; Staphylococcus aureus - pathogenicity; Virulence - genetics
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.13174

Summary Bacteria respond to ever‐changing environments through several adaptive strategies. This includes mechanisms leading to a high degree of phenotypic variability within a genetically homogeneous population. In Staphylococcus aureus, the capsular polysaccharide (CP) protects against phagocytosis, but also impedes adherence to endothelial cells and/or matrix proteins. We analysed the regulation of core biosynthesis genes (capA‐P) necessary for CP synthesis using single‐cell assays (immunofluorescence and promoter‐activity). In persistent human carriers, we found a distinct subpopulation of nasal S. aureus to be CP positive. In vitro, cap expression is also heterogeneous and strongly growth‐phase dependent. We asked whether this peculiar expression pattern (earlyOff/lateHeterogen) is orchestrated by the quorum system Agr. We show that the Agr‐driven effector molecule RNAIII promotes cap expression largely via inactivation of the repressor Rot. High NaCl, deletion of CodY or Sae also resulted in higher cap expression but did not change the earlyOFF/lateHeterogen expression pattern. Activity of the quorum system itself is largely homogenous and does not account for the observed heterogeneity of cap expression or the strictly growth phase dependent expression. Our findings are in contrast to the prevailing view that quorum sensing is the main driving force for virulence gene expression when bacterial cell densities increase. During exponential growth, cap genes involved in capsular polysaccharide biosynthesis are tightly repressed. In the later growth phase, the repressor Rot is inactivated via quorum sensing and CodY through limitation of ligands; GTP and/or branched chain amino acids. However, cap repression is only partially relieved, leaving a distinct sub‐population un‐encapsulated. Heterogeneous cap expression also occurs during human nasal colonization. Such bistability may have evolved to avoid phagocytosis (encapsulated bacteria) while simultaneously allowing adherence (non‐encapsulated bacteria).