Carbon source-dependent capsule thickness regulation in Streptococcus pneumoniae

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• The polysaccharide capsule of Streptococcus pneumoniae is crucial for virulence, adherence, and survival.
• Different carbon sources like galactose, mannose, and N-acetylglucosamine (GlcNAc) are metabolized in specific human niches (nasopharynx vs. blood).
• Understanding carbon source influence on pneumococcal growth, capsule biosynthesis, and adherence is vital.

Purpose of the Study:

• To investigate the impact of various carbon sources on Streptococcus pneumoniae growth.
• To analyze the effect of carbon sources on pneumococcal capsule biosynthesis and thickness.
• To determine how carbon sources influence the adherence potential of S. pneumoniae.

Main Methods:

• Cultured wild-type and capsule knockout S. pneumoniae strains with different carbon sources (galactose, GlcNAc, mannose, glucose).
• Measured capsule thickness using FITC-dextran exclusion assays.
• Quantified capsule precursors (UDP-glucose, UDP-galactose) via 31P-NMR and assessed epithelial adherence.
• Performed transcriptome analysis (RNA sequencing) on clinical isolates.

Main Results:

• Growth was reduced in galactose, mannose, and GlcNAc compared to glucose.
• Capsular size decreased with mannose and GlcNAc.
• Reduced accumulation of UDP-glucose and UDP-galactose precursors was observed with mannose and GlcNAc.
• Increased epithelial adherence was noted when grown in mannose versus glucose.
• Transcriptome analysis revealed strain-specific and common carbon source-specific gene expression patterns.

Conclusions:

• S. pneumoniae exhibits adaptive lifestyle strategies based on available monosaccharides in different human niches.
• Carbon source availability significantly influences pneumococcal capsule formation and adherence capabilities.
• Gene expression is modulated by carbon sources, contributing to niche adaptation.