AUTHOR=Werren Joel P. , Mostacci Nadja , Gjuroski Ilche , Holivololona Lalaina , Troxler Lukas J. , Hathaway Lucy J. , Furrer Julien , Hilty Markus 

TITLE=Carbon source–dependent capsule thickness regulation in Streptococcus pneumoniae

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=Volume 13 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1279119

DOI=10.3389/fcimb.2023.1279119

ISSN=2235-2988

ABSTRACT=Background: The polysaccharide capsule of Streptococcus pneumoniae plays a major role in virulence, adherence to epithelial cells and overall survival of the bacterium in the human host. Galactose, mannose and N-acetylglucosamine (GlcNAc) are likely to be relevant for metabolization in the nasopharynx while glucose is the primary carbon source in the blood. In this study, we aim to further the understanding of the influence of carbon sources on pneumococcal growth, capsule biosynthesis and subsequent adherence potential. 
Methods: We tested the growth behavior of clinical wild type and capsule knock out S. pneumoniae strains, using galactose, GlcNAc, mannose and glucose as carbon source for growth. We measured capsule thickness and quantified capsule precursors by fluorescein isothiocyanate (FITC)-Dextran Exclusion Assays and 31P-Nuclear Magnetic Resonance (NMR) measurements, respectively. We also performed epithelial adherence assays using Detroit 562 cells and performed a transcriptome analysis (RNA sequencing).
Results: We observed a reduced growth in galactose, mannose and GlcNAc compared to growth in glucose and found capsular size reductions in mannose and GlcNAc compared to galactose and glucose. Additionally, capsular precursor measurements of uridine diphosphate-(UDP)-glucose and UDP-galactose showed less accumulation of precursors in GlcNAc or mannose than in glucose and galactose, indicating a possible link with the received capsular thickness measurements. Epithelial adherence assays showed an increase in adherence potential for a pneumococcal strain, when grown in mannose compared to glucose. Finally, transcriptome analysis of four clinical isolates revealed strain specific but also common carbon source-specific gene expression.
Conclusion: Our findings may indicate a careful adaption of the lifestyle of S. pneumoniae according to the monosaccharides encountered in the respective human niche.