THE IMPORTANCE OF NUTRIENT ADAPTATION AND UPTAKE BY GROUP A STREPTOCOCCUS FOR ITS GROWTH AND INFECTION

Abstract

A major human-specific pathogen, Streptococcus pyogenes (Group A Streptococcus, GAS) causes a wide range of infections, from superficial to life-threatening diseases throughout different host niches. Thus, it is necessary to gain a better understanding of how GAS is able to overcome environment-specific challenges. One critical strategy for successful infection is efficient nutrient acquisition; the phosphotransferase system (PTS), which couples the import of carbohydrates with their phosphorylation, has been linked to GAS pathogenesis. In a screen of an insertional mutant library of all 14 annotated PTS permease genes in MGAS5005, the ß-glucoside PTS permease (bglP) was found important for GAS growth and survival in human blood. This was validated in another clinically relevant strain, 5448. In 5448, bglP was shown to be in an operon with a phospho-ß-glucosidase (bglB) downstream and an antiterminator (licT) upstream, with the operon repressed by glucose and induced by the ß-glucoside salicin as the sole carbon source. Investigation of individual bglPB mutants determined they influence regulation of virulence-related genes that control biofilm formation, SLS-mediated hemolysis, and localized ulcerative lesions during murine subcutaneous infections. Another nutrient acquisition system was previously identified as critical for fitness during murine soft tissue infection, the subcutaneous fitness (scf) genes CDE. This previously uncharacterized locus was transcribed as an operon and predicted to encode an ATP-Binding Cassette (ABC) importer for nutrient uptake. Individual scfCDE deletion mutants exhibited attenuation in multiple infection-related environments such as in vivo murine soft tissue infection and ex vivo whole human blood, indicating their impact is not limited to superficial infections. This was evident when vaccination with the permease mutant, scfD, resulted in protection against severe GAS invasive infection. Additionally, growth defects of scfD in nutrient-limiting chemically-defined media (CDM) could be rescued by addition of excess peptides, suggesting ScfCDE is an amino acid or peptide importer. Metabolomics and RNA-seq experiments suggested losing scfD affects multiple amino acid pathways. Since scfCDE is conserved throughout Firmicutes, this work may contribute to the development of therapeutic strategies against GAS and other Gram-positive pathogens. Overall, results indicate that the ß-glucoside PTS and ScfCDE nutrient transporters can differentially influence GAS pathophysiology during infection.