Cell Surface Glycoside Hydrolases of Streptococcus gordonii Promote Growth in Saliva

Abstract

The growth of the oral commensal Streptococcus gordonii in saliva may depend on a number of glycoside hydrolases (GHs), including three cell wall-anchored proteins that are homologs of pneumococcal ␤-galactosidase (BgaA), ␤-N-acetylglucosaminidase (StrH), and endo-␤-N-acetylglucosaminidase D (EndoD). In the present study, we introduced unmarked in-frame deletions into the corresponding genes of S. gordonii DL1, verified the presence (or absence) of the encoded proteins on the resulting mutant strains, and compared these strains with wild-type strain DL1 for growth and glycan foraging in saliva. The overnight growth of wild-type DL1 was reduced 3-to 10-fold by the deletion of any one or two genes and approximately 20-fold by the deletion of all three genes. The only notable change in the salivary proteome associated with this reduction of growth was a downward shift in the apparent molecular masses of basic proline-rich glycoproteins (PRG), which was accompanied by the loss of lectin binding sites for galactose-specific Erythrina cristagalli agglutinin (ECA) and mannose-specific Galanthus nivalis agglutinin (GNA). The binding of ECA to PRG was also abolished in saliva cultures of mutants that expressed cell surface BgaA alone or together with either StrH or EndoD. However, the subsequent loss of GNA binding was seen only in saliva cocultures of different mutants that together expressed all three cell surface GHs. The findings indicate that the growth of S. gordonii DL1 in saliva depends to a significant extent on the sequential actions of first BgaA and then StrH and EndoD on N-linked glycans of PRG. IMPORTANCEThe ability of oral bacteria to grow on salivary glycoproteins is critical for dental plaque biofilm development. Little is known, however, about how specific salivary components are attacked and utilized by different members of the biofilm community, such as Streptococcus gordonii. Streptococcus gordonii DL1 has three cell wall-anchored glycoside hydrolases that are predicted to act on host glycans. In the present study, we introduced unmarked in-frame deletions in the corresponding genes, verified the presence (or absence) of encoded proteins on the resulting mutant strains, and compared these strains with wild-type DL1 for growth and glycan foraging in saliva. The results indicate that the growth of S. gordonii DL1 depends to a significant extent on sequential action of these cell surface GHs on N-linked glycans of basic proline-rich salivary glycoproteins, which appears to be an essential first step in salivary glycan foraging. T he development of dental plaque in the absence of exogenous nutrients has long been thought to depend on bacterial foraging of host salivary glycans (1, 2). Little is known, however, about how different oral species attack and utilize salivary macromolecules as substrates for growth and whether cross-feeding between species influences dental plaque biofilm development. Recently, we compared the growth of different oral bacteria in filter-sterilized saliva that was first...

Differential Utilization of Basic Proline-Rich Glycoproteins during Growth of Oral Bacteria in Saliva

“…4 and 5), this region was shown to be highly basic, which implied it to be PRG. Conclusive identification by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was obtained in a subsequent study that examined the role of specific cell surface hydrolases in the growth of S. gordonii in saliva (27).…”

“…These species all grew poorly in our experiments. In recent studies to assess the role of cell wall-anchored GHs in salivary glycan foraging (27), we deleted genes for the three cell wall-anchored GHs of S. gordonii DL1, which are homologous to pneumococcal ␤-galactosidase (BgaA), ␤-N-acetylglucosaminidase (StrH), and endohexosaminidase D (EndoD). Importantly, the loss of these enzymes resulted in a 20-fold reduction in the growth of DL1 in saliva and abolished the degradation of PRG.…”

Glycan recognition at the saliva – oral microbiome interface

“…These strains show a preference for Nglycans linked to the proline-rich glycoprotein (PRG) [202]. For S. gordonii , this specificity for PRG is due to the sequential action of three glycoside hydrolases that are able to break down the most common glycan structure on PRG [203]. The ability to scavenge host sialic acids has also been observed in Haemophilus influenzae , Tannerella forsythia, and Vibrio cholerae .…”

Amino Sugars Reshape Interactions between Streptococcus mutans and Streptococcus gordonii

“…The copyright holder for this preprint this version posted June 23, 2020. ; https://doi.org/10.1101/2020.06.22.166272 doi: bioRxiv preprint Current research supports roles for EndoD and BgaC in the ability of S. gordonii to grow on saliva by sequentially releasing monosaccharides from the basic proline-rich glycoproteins, in concert with the activity of the β-N-acetylglucosaminidase StrH (23).…”

“…S3 for KEGG visualization). Similar to S. mutans growing on GlcN, most of these carbohydrate metabolic genes showed significantly increased expression in the presence of GlcN, including: two extracellular β-galactosidase, bgaC/EII operon (SGO_0043~SGO_0048, increased by 29~210-fold) (23,24) and bgaA (SGO_1486, increased by 9-fold)(24), two putative glucan-binding proteins (SGO_0477~SGO_0478, . CC-BY-NC-ND 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.…”