Post‐translational modification by the Pgf glycosylation machinery modulates Streptococcus mutans OMZ175 physiology and virulence

• Published in: Molecular microbiology 2024-08, Vol.122 (2), p.133-151
• Main Authors: Mojana di Cologna, Nicholas, Andresen, Silke, Samaddar, Sandip, Archer‐Hartmann, Stephanie, Rogers, Ashley Marie, Kajfasz, Jessica K., Ganguly, Tridib, Garcia, Bruna A., Saengpet, Irene, Peterson, Alexandra M., Azadi, Parastoo, Szymanski, Christine M., Lemos, José A., Abranches, Jacqueline
• Format: Article
• Language: English
• Subjects: Adhesins; Adhesins, Bacterial - genetics; Adhesins, Bacterial - metabolism; Animals; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biofilms; Biofilms - growth & development; Carrier Proteins; Cnm; Colonization; Dental caries; Dental Caries - microbiology; Gene Expression Regulation, Bacterial; Glycosylation; Glycosyltransferase; Hexosamines; Humans; Inactivation; Operon; oral colonization; Pathogenicity; Pathogens; Pgf machinery; Polysaccharides; protein glycosylation; protein phosphorylation; Protein Processing, Post-Translational; Rats; Saliva; Saliva - microbiology; Streptococcus mutans; Streptococcus mutans - genetics; Streptococcus mutans - metabolism; Streptococcus mutans - pathogenicity; Surface charge; Surface stability; Translation; Tunicamycin; Virulence
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.15190

Streptococcus mutans is commonly associated with dental caries and the ability to form biofilms is essential for its pathogenicity. We recently identified the Pgf glycosylation machinery of S. mutans, responsible for the post‐translational modification of the surface‐associated adhesins Cnm and WapA. Since the four‐gene pgf operon (pgfS‐pgfM1‐pgfE‐pgfM2) is part of the S. mutans core genome, we hypothesized that the scope of the Pgf system goes beyond Cnm and WapA glycosylation. In silico analyses and tunicamycin sensitivity assays suggested a functional overlap between the Pgf machinery and the rhamnose‐glucose polysaccharide synthesis pathway. Phenotypic characterization of pgf mutants (ΔpgfS, ΔpgfE, ΔpgfM1, ΔpgfM2, and Δpgf) revealed that the Pgf system is important for biofilm formation, surface charge, membrane stability, and survival in human saliva. Moreover, deletion of the entire pgf operon (Δpgf strain) resulted in significantly impaired colonization in a rat oral colonization model. Using Cnm as a model, we showed that Cnm is heavily modified with N‐acetyl hexosamines but it becomes heavily phosphorylated with the inactivation of the PgfS glycosyltransferase, suggesting a crosstalk between these two post‐translational modification mechanisms. Our results revealed that the Pgf machinery contributes to multiple aspects of S. mutans pathobiology that may go beyond Cnm and WapA glycosylation. The Pgf glycosylation machinery is important for several aspects of Streptococcus mutans' OMZ175 pathobiology. Also, using the adhesin Cnm as a model in glycoproteomics analyses, we report a novel crosstalk between phosphorylation and glycosylation in S. mutans.