Neuraminidase A-Exposed Galactose Promotes Streptococcus pneumoniae Biofilm Formation during Colonization

Abstract

f Streptococcus pneumoniae is an opportunistic pathogen that colonizes the nasopharynx. Herein we show that carbon availability is distinct between the nasopharynx and bloodstream of adult humans: glucose is absent from the nasopharynx, whereas galactose is abundant. We demonstrate that pneumococcal neuraminidase A (NanA), which cleaves terminal sialic acid residues from host glycoproteins, exposed galactose on the surface of septal epithelial cells, thereby increasing its availability during colonization. We observed that S. pneumoniae mutants deficient in NanA and ␤-galactosidase A (BgaA) failed to form biofilms in vivo despite normal biofilm-forming abilities in vitro. Subsequently, we observed that glucose, sucrose, and fructose were inhibitory for biofilm formation, whereas galactose, lactose, and low concentrations of sialic acid were permissive. Together these findings suggested that the genes involved in biofilm formation were under some form of carbon catabolite repression (CCR), a regulatory network in which genes involved in the uptake and metabolism of less-preferred sugars are silenced during growth with preferred sugars. Supporting this notion, we observed that a mutant deficient in pyruvate oxidase, which converts pyruvate to acetyl-phosphate under non-CCR-inducing growth conditions, was unable to form biofilms. Subsequent comparative transcriptome sequencing (RNA-seq) analyses of planktonic and biofilm-grown pneumococci showed that metabolic pathways involving the conversion of pyruvate to acetyl-phosphate and subsequently leading to fatty acid biosynthesis were consistently upregulated during diverse biofilm growth conditions. We conclude that carbon availability in the nasopharynx impacts pneumococcal biofilm formation in vivo. Additionally, biofilm formation involves metabolic pathways not previously appreciated to play an important role.

Streptococcus pneumoniae: transmission, colonization and invasion

“…The production of an extracellular matrix has a major impact on the ability of S. pneumoniae that has been grown in a biofilm in vitro to subsequently translocate from the nasopharynx to the lungs in a murine infection model 111 . A recent report has also suggested that NanA-mediated cleavage of sialic acid promotes biofilm formation in vivo and increases carbon availability during colonization 112 . Murine experiments suggested that the large surface-exposed glycoprotein PsrP is particularly important for bacterial attachment to lung cells and biofilm formation by intraspecies interaction 113 .…”

Glycan‐metabolizing enzymes in microbe–host interactions: the Streptococcus pneumoniae paradigm

“…However, there is also a wealth of evidence to show that the role of Nglycan degradation in the host-pathogen interaction extends beyond nutrition. NanA, as the initiator of complex N-glycan degradation, has been identified as a key virulence factor in S. pneumoniae that contributes to adherence [69,78,[80][81][82], biofilm formation [81][82][83][84], tissue invasion [69,85], colonization [82,[86][87][88][89], persistence [86,87], immune Box 2. NanA, as the initiator of complex N-glycan degradation, has been identified as a key virulence factor in S. pneumoniae that contributes to adherence [69,78,[80][81][82], biofilm formation [81][82][83][84], tissue invasion [69,85], colonization [82,[86][87][88][89], persistence [86,87], immune Box 2.…”

“…Like NanA, the role of BgaA in virulence appears to be multifaceted; however, the greatest evidence exists for its contribution to adherence (Table 1) [47,70,78,84]. The adherence function of BgaA has been mapped to its two CBMs [47] (Box 1).…”

Position of O-Acetylation within the Capsular Repeat Unit Impacts the Biological Properties of Pneumococcal Serotypes 33A and 33F

“…Biofilm formation by the serotype 33A variants was measured as previously described (69). Briefly, bacteria from blood agar plates were grown to an OD 600 of 0.2 (approximately 1 ϫ 10 8 CFU/ml).…”