Streptococcus gordoniiDL1 adhesin SspB V‐region mediates coaggregation via receptor polysaccharide of Actinomyces oris T14V

Abstract

Streptococcus gordonii SspA and SspB proteins, members of the antigen I/II (AgI/II) family of Streptococcus adhesins, mediate adherence to cysteine-rich scavenger glycoprotein gp340 and cells of other oral microbial species. In this article we investigated further the mechanism of coaggregation between S. gordonii DL1 and Actinomyces oris T14V. Previous mutational analysis of S. gordonii suggested that SspB was necessary for coaggregation with A. oris T14V. We have confirmed this by showing that Lactococcus lactis surrogate host cells expressing SspB coaggregated with A. oris T14V and PK606 cells, while L. lactis cells expressing SspA did not. Coaggregation occurred independently of expression of A. oris type 1 (FimP) or type 2 (FimA) fimbriae. Polysaccharide was prepared from cells of A. oris T14V and found to contain 1,4-, 4,6- and 3,4-linked glucose, 1,4-linked mannose, and 2,4-linked galactose residues. When immobilized onto plastic wells this polysaccharide supported binding of L. lactis expressing SspB, but not binding of L. lactis expressing other AgI/II family proteins. Purified recombinant NAVP region of SspB, comprising amino acid (aa) residues 41-847, bound A. oris polysaccharide but the C-domain (932-1470 aa residues) did not. A site-directed deletion of 29 aa residues (Δ691-718) close to the predicted binding cleft within the SspB V-region ablated binding of the NAVP region to polysaccharide. These results infer that the V-region head of SspB recognizes an actinomyces polysaccharide ligand, so further characterizing a lectin-like coaggregation mechanism occurring between two important primary colonizers.

A commensal streptococcus hijacks a Pseudomonas aeruginosa exopolysaccharide to promote biofilm formation

“…gordonii adhesin, SspB, is directly involved in interacting with the Mfa1 surface protein of Porphyromonas gingivalis to promote P . gingivalis biofilm formation, and also mediates binding to an Actinomyces oris -derived polysaccharide [31–33]. However, unlike previous studies that demonstrate adhesin-specific interactions between bacteria that are generally specific to the oral cavity, our study highlights a unique association between an oral bacterial adhesin and a polysaccharide produced by a traditionally non-oral bacterium.…”

Interactions between Streptococcus oralis, Actinomyces oris, and Candida albicans in the development of multispecies oral microbial biofilms on salivary pellicle

“…It is possible that there are additional coaggregation mechanisms between A. oris T14V and S. oralis 34 that are secondary to the fimbriae-RPS interaction. For example, we have recently shown that the Streptococcus gordonii SspB (antigen I/II-family) protein binds to a polysaccharide receptor present on A. oris T14V (Back et al, 2015). Streptococcus oralis 34 also carries an antigen I/II protein-encoding gene, and so the S. oralis antigen I/II protein might act similarly.…”

Transcriptional responses of Streptococcus gordonii and Fusobacterium nucleatum to coaggregation

“…In some cases, strong coaggregation is mediated by interactions between one type of adhesin and a complementary receptor. For example, S. gordonii DL1 SspB is necessary and sufficient for binding to an Actinomyces oris MG1 cell surface carbohydrate and mediating coaggregation . Other coaggregation interactions involve multiple proteins and/or carbohydrates.…”

“…For example, S. gordonii DL1 SspB is necessary and sufficient for binding to an Actinomyces oris MG1 cell surface carbohydrate and mediating coaggregation. 7,8 Other coaggregation interactions involve multiple proteins and/or carbohydrates. Recent evidence indicates that coaggregation between Fusobacterium nucleatum and S. gordonii involves at least three F. nucleatum outer membrane proteins: two arginine-inhibitable adhesins, RadD and CmpA, and an accessory protein Aid1 that facilitates RadD-mediated adhesion.…”