B-271. Transport of Glycoconjugate-Derived Monosaccharides by Streptococcus pneumoniae

S. J. King1,2, A. M. Burnaugh1;
1The Res. Inst. at Nationwide Children’s Hosp., Columbus, OH, 2The Ohio State Univ. Coll. of Med., Columbus, OH.

The human pathogen Streptococcus pneumoniae (Sp) colonizes the human oro-nasopharynx as a necessary first step in pathogenesis. It is unknown how Sp colonizes the upper airway, which is largely devoid of free sugars for Sp metabolism. We proposed that glycoconjugates abundant in the oro-nasopharynx serve as a carbon source for Sp during colonization. We recently demonstrated that Sp uses glycoconjugates as a sole carbon source for growth, and that this growth depends on the release of monosaccharides by Sp exoglycosidases. This study aims to identify transporters responsible for the uptake of sialic acid (SA), galactose (Gal) and N-acetylglucosamine (GlcNAc), the three sugars liberated from complex N-linked glycans. Growth of Sp on chemically defined medium (CDM) supplemented with SA, Gal, or GlcNAc as the sole carbon source demonstrated that all three sugars can sustain Sp growth. In order to identify relevant transporters, unmarked, non-polar, deletions of putative SA, Gal, and GlcNAc transporter genes were constructed. Single mutants in two ATP-binding cassette (ABC) transporters associated with the nanA and nanB loci were significantly reduced in growth on SA compared to wild type. A mutant in both ABC transporters exhibited no growth on SA, demonstrating that these genes are essential for Sp growth on SA. Additionally, our data confirm the previous identification of the Gal transporter (SPR0562-65). However, neither the previously predicted GlcNAc transporter (SPR0291, 0293-95) nor a transporter located downstream of strH in the genome (SPR0059-63) are required for growth of Sp on GlcNAc in our system. Investigations are currently under way to identify the GlcNAc transporter(s), as well as to investigate all of the identified transporters using radio-labeled sugars. In this study, we have identified two ABC transporters required for Sp growth on SA. Further investigation into the transport of glycoconjugate-derived monosaccharides will increase our knowledge of pneumococcal growth and colonization in the upper respiratory tract, and may open the door to new therapeutic techniques.