Project description:Small distortions in transcriptional networks might lead to drastic phenotypical changes, especially in cellular developmental programs such as competence for natural transformation. Here, we report a pervasive circuitry rewiring for competence and predation interplay in commensal streptococci. Canonically, in model species of streptococci such as Streptococcus pneumoniae and Streptococcus mutans, the pheromone-based two-component system BlpRH is a central node that orchestrates the production of antimicrobial compounds (bacteriocins) and incorporates signal from the competence activation cascade. However, the human commensal Streptococcus salivarius does not contain a functional BlpRH pair and in this species, the competence signaling system ComRS directly couples bacteriocin production and competence commitment. This network shortcut might account for an optimal reaction against microbial competitors and could explain the high prevalence of S. salivarius in the human digestive tract. Moreover, the broad spectrum of bacteriocin activity against pathogenic bacteria showcases the commensal and genetically tractable S. salivarius species as a user-friendly model for natural transformation and bacterial predation. Overall design: Examination of mRNA transcriptional profiles in WT and 2 mutant strains activated with a pheromone + Examination of small RNA transcriptional profiles in WT with or without pheromone induction
Project description:The human oral cavity is one of the most competing environments, considering the extent and diversity of the bacterial community that colonizes it, as well as the multiple stresses to which it is subjected. The commensal species Streptococcus salivarius is one of the first colonizers of the oral mucosa (tongue, gums, inner cheeks and tooth enamel) in infants and remains predominant throughout the life of an adult. In order to adapt to diverse and variable environmental conditions, S. salivarius triggers in a coordinated way two bacterial developmental processes: competence (acquisition of extracellular DNA and new genetic traits) and predation (secretion of cytotoxic molecule), via ComR, a transcription factor activatable by a "pheromone" peptide. Nevertheless, the activation of other transcriptional regulators can uncouple these 2 mechanisms to allow, for example, only the production of toxins without triggering the competence phase. Overall design: Examination of mRNA transcriptional profiles in WT and 2 deletion and 2 overexpression mutant strains.
Project description:In streptococcal species, the key step of competence development is the transcriptional induction of comX, which encodes the alternative sigma factor sigma(X), which positively regulates genes necessary for DNA transformation. In Streptococcus species belonging to the mitis and mutans groups, induction of comX relies on the activation of a three-component system consisting of a secreted pheromone, a histidine kinase, and a response regulator. In Streptococcus thermophilus, a species belonging to the salivarius group, the oligopeptide transporter Ami is essential for comX expression under competence-inducing conditions. This suggests a different regulation pathway of competence based on the production and reimportation of a signal peptide. The objective of our work was to identify the main actors involved in the early steps of comX induction in S. thermophilus LMD-9. Using a transcriptomic approach, four highly induced early competence operons were identified. Among them, we found a Rgg-like regulator (Ster_0316) associated with a nonannotated gene encoding a 24-amino-acid hydrophobic peptide (Shp0316). Through genetic deletions, we showed that these two genes are essential for comX induction. Moreover, addition to the medium of synthetic peptides derived from the C-terminal part of Shp0316 restored comX induction and transformation of a Shp0316-deficient strain. These peptides also induced competence in S. thermophilus and Streptococcus salivarius strains that are poorly transformable or not transformable. Altogether, our results show that Ster_0316 and Shp0316, renamed ComRS, are the two members of a novel quorum-sensing system responsible for comX induction in species from the salivarius group, which differs from the classical phosphorelay three-component system identified previously in streptococci.
Project description:Streptococcus salivarius strains are significant contributors to the human oral microbiome. Some possess unique fimbriae that give them the ability to coaggregate and colonize particular oral structures. We present here the complete genomes of Streptococcus salivarius Lancefield K-/K+ strains ATCC 25975 and ATCC 27945, which can and cannot, respectively, produce fimbriae.
Project description:The oral microbial flora consists of many beneficial species of bacteria that are associated with a healthy condition and control the progression of oral disease. Cooperative interactions between oral streptococci and the pathogens play important roles in the development of dental biofilms in the oral cavity. To determine the roles of oral streptococci in multispecies biofilm development and the effects of the streptococci in biofilm formation, the active substances inhibiting Streptococcus mutans biofilm formation were purified from Streptococcus salivarius ATCC 9759 and HT9R culture supernatants using ion exchange and gel filtration chromatography. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry analysis was performed, and the results were compared to databases. The S. salivarius HT9R genome sequence was determined and used to indentify candidate proteins for inhibition. The candidates inhibiting biofilms were identified as S. salivarius fructosyltransferase (FTF) and exo-beta-d-fructosidase (FruA). The activity of the inhibitors was elevated in the presence of sucrose, and the inhibitory effects were dependent on the sucrose concentration in the biofilm formation assay medium. Purified and commercial FruA from Aspergillus niger (31.6% identity and 59.6% similarity to the amino acid sequence of FruA from S. salivarius HT9R) completely inhibited S. mutans GS-5 biofilm formation on saliva-coated polystyrene and hydroxyapatite surfaces. Inhibition was induced by decreasing polysaccharide production, which is dependent on sucrose digestion rather than fructan digestion. The data indicate that S. salivarius produces large quantities of FruA and that FruA alone may play an important role in multispecies microbial interactions for sucrose-dependent biofilm formation in the oral cavity.
Project description:A CadDX system that confers resistance to Cd(2+) and Zn(2+) was identified in Streptococcus salivarius 57.I. Unlike with other CadDX systems, the expression of the cad promoter was negatively regulated by CadX, and the repression was inducible by Cd(2+) and Zn(2+), similar to what was found for CadCA systems. The lower G+C content of the S. salivarius cadDX genes suggests acquisition by horizontal gene transfer.
Project description:Streptococcus salivarius is an abundant isolate of the oral cavity. The genome of S. salivarius 57.I consists of a 2-Mb chromosome and a 40,758-bp circular molecule, designated YMC-2011. Annotation of YMC-2011 revealed 55 open reading frames, most of them associated with phage production, although plaque formation is not observed in S. salivarius 57.I after lytic induction using mitomycin C. Results from Southern hybridization and quantitative real-time PCR confirmed that YMC-2011 exists extrachromosomally, with an estimated copy number of 3 to 4. Phage particles were isolated from the supernatant of mitomycin C-treated S. salivarius 57.I cultures, and transmission electron microscopic examination indicated that YMC-2011 belongs to the Siphoviridae family. Phylogenetic analysis suggests that phage YMC-2011 and the cos-type phages of Streptococcus thermophilus originated from a common ancestor. An extended -10 element (p L ) and a ?70-like promoter (p R ) were mapped 5' to Ssal_phage00013 (encoding a CI-like repressor) and Ssal_phage00014 (encoding a hypothetical protein), respectively, using 5' rapid amplification of cDNA ends, indicating that YMC-2011 transcribes at least two mRNAs in opposite orientations. Studies using promoter-chloramphenicol acetyltransferase reporter gene fusions revealed that p R , but not p L , was sensitive to mitomycin C induction, suggesting that the switch from lysogenic growth to lytic growth was controlled mainly by the activity of these two promoters. In conclusion, a lysogenic state is maintained in S. salivarius 57.I, presumably by the repression of genes encoding proteins for lytic growth.IMPORTANCE The movement of mobile genetic elements such as bacteriophages and the establishment of lysogens may have profound effects on the balance of microbial ecology where lysogenic bacteria reside. The discovery of phage YMC-2011 from Streptococcus salivarius 57.I suggests that YMC-2011 and Streptococcus thermophilus-infecting phages share an ancestor. Although S. salivarius and S. thermophilus are close phylogenetically, S. salivarius is a natural inhabitant of the human mouth, whereas S. thermophilus is commonly found in the mammary mucosa of bovine species. Thus, the identification of YMC-2011 suggests that horizontal gene transfer via phage infection could take place between species from different ecological niches.
Project description:Streptococcus salivarius is a nonpathogenic Gram-positive bacterium and the predominant colonizer of the oral microbiota. It finds a wide application in the prevention of upper respiratory tract infections, also reducing the frequency of other main pathogens. Here, we present the complete genome sequence of the oral probiotic S. salivarius JF.
Project description:Streptococcus salivarius is a commensal species commonly found in the human oral cavity and digestive tract, although it is also associated with human infections such as meningitis, endocarditis, and bacteremia. Here, we report the complete sequence of S. salivarius strain CCHSS3, isolated from human blood.
Project description:Salivaricin G32, a 2667?Da novel member of the SA-FF22 cluster of lantibiotics, has been purified and characterized from Streptococcus salivarius strain G32. The inhibitory peptide differs from the Streptococcus pyogenes-produced SA-FF22 in the absence of lysine in position 2. The salivaricin G32 locus was widely distributed in BLIS-producing S. salivarius, with 6 (23%) of 26 strains PCR-positive for the structural gene, slnA. As for most other lantibiotics produced by S. salivarius, the salivaricin G32 locus can be megaplasmid encoded. Another member of the SA-FF22 family was detected in two Streptococcus dysgalactiae of bovine origin, an observation supportive of widespread distribution of this lantibiotic within the genus Streptococcus. Since the inhibitory spectrum of salivaricin G32 includes Streptococcus pyogenes, its production by S. salivarius, either as a member of the normal oral microflora or as a commercial probiotic, could serve to enhance protection of the human host against S. pyogenes infection.