ABSTRACT The extracellular molecular landscape of oral bacteria remains underexplored beyond canonical secreted proteins. Here, we show that sucrose reshapes the culture‐supernatant protein–peptide output of the cariogenic pathobiont Streptococcus mutans UA159. Integrating proteomics with stringent peptidomic source assignment revealed that sucrose remodeled the supernatant‐detectable proteome toward surface/envelope‐ and cell‐wall‐associated features while reducing cytoplasmic, metabolic, and glucosyltransferase‐associated signatures. In parallel, sucrose was associated with a distinct endogenous peptide layer. Among 34 stringently defined UA159‐derived peptide candidates, 19 mapped to signal peptide regions, and many were preferentially detected under the sucrose condition. Functional screening of 16 successfully synthesized candidates identified two BHIS‐associated signal‐peptide‐region peptides, SmuG15 and SmuV13, that reduced biofilm biomass and glucan‐associated matrix signals when supplied exogenously, without detectable inhibition of planktonic growth in brain heart infusion (BHI). This separation between planktonic‐growth and biofilm phenotypes is consistent with a biofilm‐associated effect rather than detectable bacteriostatic activity under the planktonic‐growth conditions tested. Together, these findings identify culture‐supernatant peptides as sucrose‐responsive extracellular outputs and highlight peptide candidates whose synthetic counterparts showed antibiofilm activity upon exogenous application. The study expands the molecular view of sucrose‐driven cariogenic adaptation and provides a framework for discovering functional peptides from bacterial extracellular compartments.
ABSTRACT Understanding how S. mutans adapts to environmental stresses is key to deciphering its cariogenic virulence. Here, we report that alcohol‐acetaldehyde dehydrogenase (AdhE) modulates the stress adaptability in S. mutans by regulating a metabolic‐acetylation axis. We demonstrated that overexpression of adhE sensitizes S. mutans to H 2 O 2 and high temperature, impairing planktonic growth and biofilm integrity under oxidative and heat stress. Mechanistically, AdhE functions as a potential acetyl‐CoA (Ac‐CoA) synthase, with its overexpression elevating intracellular Ac‐CoA levels. Quantitative acetylomics revealed that elevated Ac‐CoA drives extensive protein acetylation, hyperacetylating 340 proteins. Protein interaction network analysis identified core antioxidant enzymes (Tpx, Dpr, TrxA/B, AhpC) and heat‐shock chaperones (DnaJ, GroEL, ClpE) as major targets, linking hyperacetylation to compromised stress defenses. Crucially, in a rat caries model, adhE overexpression attenuated the cariogenic virulence of S. mutans , reducing oral colonization and caries severity, an effect exacerbated by H 2 O 2 challenge. Collectively, these findings uncover AdhE as a metabolic regulator that bridges Ac‐CoA availability, global protein acetylation, and stress adaptation, offering new insights into posttranslational control of bacterial fitness and potential anti‑caries targets.
ABSTRACT While Th1 and Th17 cells are well known for their distinct roles in host defense, how these effector CD4 + T‐cell subsets influence epithelial responses to intracellular bacteria remains unclear. Here, we investigated whether Th1 or Th17 cells modulate the intracellular survival of Escherichia coli 7.2 (Ec7.2), a clinical isolate from oral lichen planus (OLP) tissue, in oral keratinocytes. To assess antigen‐specific and antigen‐independent T‐cell effects, we established a co‐culture system using IFN‐γ‐pretreated, Ec7.2‐infected immortalized murine oral keratinocytes (IMOK) and Th1 or Th17 cells differentiated from OT‐II‐restricted CD4 + T cells, in the absence or presence of cognate peptide. Th1 cells reduced intracellular Ec7.2 in an antigen‐dependent manner, whereas Th17 cells consistently increased bacterial persistence through largely antigen‐independent and contact‐independent mechanisms. Transcriptomic analysis of infected IMOK cells revealed that Th17‐associated soluble signals broadly attenuated epithelial innate immune and antibacterial responses, including pathways related to type II interferon signaling, chemokine production, and defense response to bacterium. Among these, Nos2 expression was significantly reduced upon Th17 co‐culture and was accompanied by decreased nitric oxide (NO) production. Th17 cells expressed higher levels of Tgfb1 than Th1 cells, and elevated TGF‐β concentrations were consistently observed under Th17 co‐culture conditions associated with increased bacterial persistence. Neutralization of TGF‐β was associated with a trend toward increased NO production and reduced intracellular Ec7.2 recovery relative to isotype‐treated controls. Together, these findings identify a previously underappreciated role for Th17–associated signals in modulating epithelial defense against intracellular bacteria, in part through TGF‐β–associated suppression of NO‐associated antimicrobial responses, which may contribute to bacterial persistence in Th17‐dominated mucosal environments.
ABSTRACT Background Streptococcus mutans ( S. mutans ) is a primary etiological agent in dental caries. However, longitudinal evidence regarding its role in caries initiation and progression remains limited. This study aimed to evaluate the utility of the muf biosynthetic gene cluster (BGC) in S. mutans as a predictor of caries occurrence and progression. Methods We first conducted a case–control study to assess the prevalence of the muf BGC using quantitative polymerase chain reaction (qPCR). Subsequently, a prospective cohort study was performed to evaluate the cariogenic potential of muf . Caries increment over the follow‐up period was compared between children harboring muf ‐positive and muf ‐negative S. mutans . Results Initial screening targeting the glucosyltransferase B (gtfB) gene confirmed the presence of S. mutans . Among the 46 S. mutans ‐positive specimens, the prevalence of the muf locus was higher in children with caries (44.12%, 15/34) than in caries‐free controls (16.67%, 2/12), corresponding to an odds ratio (OR) of 3.95. In the prospective cohort of 119 children, univariate analysis revealed that muf ‐positivity was associated with a 2.13‐fold increased risk of caries increment over the 6‐month follow‐up (60.7% vs. 28.6%, p < 0.01). Importantly, this association remained robust after multivariable adjustment for potential confounders, with muf ‐positivity continuing to confer nearly twice the risk of developing new carious lesions ( p < 0.01). Furthermore, an integrated risk stratification framework identified the double‐positive ( muf + /gtfB + ) genotype as a high‐risk factor for caries progression, yielding an RR of 6.21 compared to the muf − /gtfB − baseline. Conclusions BGC m uf ‐positive S. mutans is associated with increased caries progression in early childhood, highlighting its potential as a biomarker for identifying high‐risk individuals.
ABSTRACT High genetic variability in streptococci is driven by natural competence, specifically in Streptococcus pneumoniae and its close commensal species ( Streptococcus pseudopneumoniae , Streptococcus oralis , and Streptococcus mitis ), which drives rapid Streptococcal evolution. The genome of S. pneumoniae and its close commensal species exhibits high interspecies recombination, an open‐pan genome, and a similar evolutionary origin. Mechanisms of natural competence are a highly regulated process driven by numerous molecular players at different stages. Natural competence in Streptococci drives the shift from commensal to pathogenic state. Streptococcus pneumoniae acquires various virulence and antibiotic‐resistant genes (ARGs) via natural competence and also facilitates immune evasion, the emergence of multidrug‐resistant strains, and capsule switching between strains. Most reports indicated that the natural competence in S. pneumoniae is a one‐way street process; however, a few studies have proved that it is a two‐way street process. The purpose of the current review is to elucidate (i) the genome of S. pneumoniae and its close relatives, (ii) the mechanism of HGT, (iii) HGT in S. pneumoniae and related commensal species, (iv) acquisition of drug‐resistance genes and virulence factors, and (v) the implication of HGT in competence‐driven gene transfer in IPD and interaction between host and pathogens.
