Project description:Streptococcus sobrinus is an etiologic cause of dental caries (tooth decay) in humans. Our knowledge of S. sobrinus is scant despite the organism's important role in oral health. It is widely believed that S. sobrinus lacks the natural competence pathways that are used by other streptococci to regulate growth, virulence, and quorum sensing. The lack of natural competence has also prevented genetic manipulation of S. sobrinus, limiting our knowledge of its pathogenicity. We discovered that most strains of S. sobrinus contain a new class of the ComRS competence system. Although S. sobrinus is typically placed among the mutans group streptococci, the S. sobrinus ComRS system is most similar to the competence pathways in the salivarius group. Unlike all other ComRS systems, the S. sobrinus pathway contains 2 copies of the transcriptional regulator ComR and has a peptide pheromone (XIP) that lacks any aromatic amino acids. Synthetic XIP enables transformation of S. sobrinus with plasmid or linear DNA, and we leverage this newfound genetic tractability to confirm that only 1 of the ComR homologs is required for induced competence while the other appears to suppress competence. Exogenous XIP increases the expression of bacteriocin gene clusters and produces an antimicrobial response that inhibits growth of S. mutans. We also identified 2 strains of S. sobrinus that appear to be "cheaters" by either not responding to or not producing XIP. We show how a recombination event in the nonresponsive strain could restore function of the ComRS pathway but delete the gene encoding XIP. Thus, the S. sobrinus ComRS pathway provides new tools for studying this pathogen and offers a lens into the evolution of ecological cheaters.

| S-EPMC8060777 | biostudies-literature

Identification of NAD+ synthetase from Streptococcus sobrinus as a B-cell-stimulatory protein.

Project description:Streptococcus sobrinus, one agent of dental caries, secretes a protein that induces lymphocyte polyclonal activation of the host as a mechanism of immune evasion. We have isolated from culture supernatants of this bacterium a protein with murine B-cell-stimulatory properties and subsequently cloned the relevant gene. It contains an open reading frame of 825 bp encoding a polypeptide with 275 amino acid residues and a molecular mass of 30 kDa. The protein displays high sequence homology with NAD(+) synthetases from several organisms, including a conserved fingerprint sequence (SGGXD) characteristic of ATP pyrophosphatases. The polypeptide was expressed in Escherichia coli as a hexahistidine-tagged protein and purified in an enzymatically active form. The recombinant NAD(+) synthetase stimulates murine B cells after in vitro treatment of spleen cell cultures, as demonstrated by its ability to induce up-regulation of the expression of CD69, an early marker of lymphocyte activation. Stimulation with the recombinant NAD(+) synthetase was also observed with other B-cell markers, such as CD19(+), B220(+), and CD21(+). Cell proliferation follows the activation induced by the recombinant NAD(+) synthetase.

| S-EPMC305756 | biostudies-literature

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