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PubMed2026

An XRE-type regulator in Streptococcus mutans plays an important role in brpA expression and oxidative stress tolerance response.

This study used a functional genomics approach to explore the role of a xenobiotic response element (XRE)-type regulator (SMU.405c) in Streptococcus mutans physiology, including the expression of biofilm regulatory protein BrpA. Results showed that deletional mutation of xre significantly reduced the ability of the deficient mutant to grow in the presence of methyl viologen, a commonly used oxidative stressor (P < 0.001). When challenged in a hydrogen peroxide killing assay, the survival rate of the ∆xre mutant was >2-log less than the parent strain after 60 min (P < 0.001). Luciferase reporter fusion assays showed that xre deficiency had no significant effect on luciferase expression when it was under the control of the intact brpA promoter, but the reporter activity increased by >6-fold (P < 0.001) when the reporter gene was fused to a brpA promoter derivative with deletion of a putative XRE-binding box. Electrophoretic mobility shift assay (EMSA) showed that recombinant XRE interacted with the brpA promoter, resulting in an electrophoretic shift of the promoter probes. In vitro transcription assay also showed that inclusion of XRE caused transcription to fall off, significantly reducing full-length brpA transcripts. RNA-seq analysis revealed that deficiency of XRE led to altered expression of >102 genes by >2-fold (P < 0.05), including 28 with increased expression, and 74 with decreased expression. Among the down-regulated were genes for DNA repair and oxidative stress tolerance response. These results suggest that XRE (SMU.405c) in S. mutans plays an important role in brpA expression and oxidative stress tolerance response.IMPORTANCEStreptococcus mutans, a keystone pathogen in human dental caries, primarily lives in the highly diverse microbiota on tooth surfaces, where the conditions are often harsh and fluctuate frequently. Locus SMU.405c was annotated to encode a xenobiotic response element (XRE)-like transcriptional regulator, but no information is available concerning the role of this protein in S. mutans pathophysiology. This study used a functional genomics approach along with molecular and transcriptomic analysis to characterize a deletional xre mutant, and the results showed that xre deficiency in S. mutans resulted in weakened oxidative stress tolerance response and alterations in transcription of >102 genes, including those known to play an important role in cell envelope biogenesis and stress tolerance response. Reporter fusion assay, electrophoretic mobility shift assay (EMSA), and in vitro transcription further demonstrated that the XRE-like regulator encoded by SMU.405c is a repressor of brpA expression and plays an important role in oxidative stress tolerance response.

Streptococcus mutans↗

PubMed2026

Identification of a putative RocS homolog through phenotypic profiling of uncharacterized essential genes in Streptococcus mutans.

Genome-wide viability catalogs produced by transposon sequencing (Tn-seq) and CRISPR interference (CRISPRi) have successfully mapped the essential genome of Streptococcus mutans . In this study, we combined predictive bioinformatics, conditional CRISPRi transcriptional silencing, transmission electron microscopy, transcriptomics, and genetic suppressor screens to investigate nine poorly characterized essential genes in S. mutans . From this screen, phenotypic and genetic analyses identified SMU_393 as a functional homolog of the pneumococcal chromosome segregation factor, RocS. Depletion of SMU_393 resulted in abnormal cell widening, hypersensitivity to DNA damage, and a significant subpopulation of anucleate cells. These phenotypes were bypassed by a spontaneous surface-exposed missense mutation ( dnaA Q197E ) within the AAA+ ATPase domain of the replication initiator. Together, this study refines annotations within the S. mutans essential genome and provides genetic insights into streptococcal chromosome segregation and cell cycle control.

Journal Article↗

PubMed2025

SloR-SRE binding to the S. mutans mntH promoter is cooperative.

UNLABELLED: Streptococcus mutans is a commensal member of the plaque microbiome. It is especially prevalent when dietary sugars are available for S. mutans fermentation, generating acid byproducts that lower plaque pH and foster tooth decay. S. mutans can survive in the transient conditions of the mouth, in part because it can regulate the uptake of manganese and iron during periods of feast when metal ions are available, and famine when they are limited. S. mutans depends on a 25kDa metalloregulatory protein, called SloR, to modulate the uptake of these cations across the bacterial cell surface. When bound to manganese, SloR binds to palindromic recognition elements in the promoter of the sloABC genes that encode the major manganese transporter in S. mutans. Reports in the literature describe MntH, an ancillary manganese transporter in S. mutans, that is also subject to SloR control. In the present study, we performed expression profiling experiments that reveal coordinate regulation of the sloABC and mntH genes at the level of transcription. In addition, we describe a role for the mntH gene product that is redundant with that of the sloABC-encoded metal ion uptake machinery. The results of DNA-binding studies support direct SloR binding to the mntH promoter region which, like that at the sloABC promoter, harbors three palindromic recognition elements to which SloR binds cooperatively to repress downstream transcription. These findings expand our understanding of the SloR metalloregulome and elucidate SloR-DNA binding that is essential for S. mutans metal ion homeostasis and fitness in the oral cavity. IMPORTANCE: Dental caries disproportionately impacts low-income socioeconomic groups in the United States and abroad. Research that is focused on S. mutans, the primary causative agent of dental caries in humans, is significant to mitigation efforts aimed at alleviating or preventing dental caries. The SloR protein is a major regulator of the S. mutans metal ion uptake machinery encoded by the sloABC- and mntH genes. This SloR-mediated gene control is essential for maintaining intracellular metal ion homeostasis, and hence S. mutans fitness in the plaque microbiome. An improved understanding of the sloABC and mntH metal ion transporters and their regulation by SloR can guide rational drug design that, by targeting the SloR-DNA-binding interface, can alleviate or prevent S. mutans-induced disease.

Streptococcus mutans↗

PubMed2026

A genome-wide in vivo screen reveals fitness pathways required for streptococcal infective endocarditis.

Infective endocarditis (IE) is a life-threatening disease most often caused by blood-borne bacteria that infect previously damaged cardiac tissue. Despite the importance of this disease, the genetic basis for IE-associated fitness remains poorly defined. Here, we present the first genome-wide in vivo analysis of bacterial fitness in a vertebrate model of IE. We identified 146 genes in Streptococcus sanguinis required for IE fitness, the majority of which had not previously been linked to endocarditis. These determinants cluster into conserved metabolic, cell envelope, transport, and regulatory pathways, representing a vast reservoir of potential targets for novel antimicrobial intervention. A subset of these genes was examined in Streptococcus mutans; all were found to be essential for IE fitness in this distantly related oral species as well, suggesting broad conservation. Using experimental evolution, we further show that disruption of key fitness pathways triggers reproducible compensatory "bypass" mechanisms. Together, these findings provide a comprehensive, genome-wide map of the bacterial niche-requirements for streptococcal infective endocarditis.

Animals↗

PubMed2026

Evaluation of Indigenous Bacillus Strains from Asian Fermented Foods for Probiotic Properties.

Bacillus species hold particular importance due to their versatile enzymatic repertoire and ability to synthesize diverse bioactive metabolites. In this study, two fermented food-derived strains, Bacillus siamensis BB3 (from douchi) and Bacillus velezensis TMA10 (from tapai) were evaluated for their probiotic, anti-microbial and functional potentials. Both strains exhibited desirable probiotic characteristics, including desirable tolerance to simulated gastric and intestinal conditions, with BB3 showing greater acid tolerance than TMA10. Safety assessments confirmed the absence of hemolytic activity, virulence factors and antibiotic resistance genes. Whole genome sequencing showed that the strains harbored genomic sequences for a wide range of metabolites, including non-ribosomal peptides and polyketides. Ethyl acetate (EtOAc) extracts from both strains demonstrated broad-spectrum anti-microbial activity against several indicator microorganisms, including Listeria grayi, Bacillus cereus, Serratia marcescens, Escherichia coli, and Pseudomonas aeruginosa, with TMA10 additionally inhibiting MRSA and Streptococcus mutans. Liquid Chromatography-Mass Spectrometry profiling identified key anti-microbial compounds, namely surfactins, macrolactins, bacillaene from BB3 and TMA10. In addition, difficidins were also detected from TMA10. Genomic analysis further indicated diverse carbohydrate utilization capacities; both strains encoded pathways for sucrose, raffinose-family oligosaccharides and lactose metabolism, while TMA10 possessed pathways for trehalose, glucomannan and arabinoxylan degradation. Both strains also showed anti-oxidant activity, with enhanced effects observed in their cell-free supernatants and heat-killed preparations. Overall, these findings highlight BB3 and TMA10 as promising candidates for the development of fermented food-derived Bacillus probiotics and functional cultures with anti-microbial, anti-oxidant, and broad carbohydrate-utilization capabilities.

Bacillus↗

PubMed2026

Pre-clinical evaluation of the anticaries effect of an experimental Malva sylvestris extract mouthwash using a cariogenic model in situ.

OBJECTIVE: The aim of this study was to evaluate the antimicrobial and anticariogenic potential of Malva sylvestris extract on enamel and dentin in situ. METHODS: A double-blind crossover in situ study was conducted with 12 participants wearing palatal appliances containing two bovine enamel and two dentin specimens per 3 phases, a total of 72 enamel and dentin specimens. Biofilm formation and daily sucrose exposure were allowed. Treatments were applied twice daily in three phases: Malva sylvestris (2.5%, MS); fluoride (225 ppm, F); and placebo (P). After seven days, biofilm was collected from the bovine specimens for analysis of Lactobacillus spp. and mutans streptococci by Colony Forming Unit counts (CFU log₁₀/mL). Dental demineralization of the bovine specimens was assessed by transverse microradiography (TMR). RESULTS: MS did not reduce Lactobacillus spp. counts (CFU log₁₀/mL: enamel 6.63±0.81; dentin 6.68±0.92) compared to P (6.63±0.70; 6.62±0.51). F also did not differ (6.29±0.75; 6.32±0.41; ANOVA/Tukey, p>0.38). Mutans streptococci data were inconclusive. In enamel, both MS (2320.8±768.2 %vol·µm; 101.6±27.0 µm) and F (1777.3±733.3 %vol·µm; 95.8±23.5 µm) significantly reduced integrated mineral loss and lesion depth compared to P (3517.2±1119.9 %vol·µm; 138.6±19.5 µm; ANOVA/Tukey, p≤0.0003). In dentin, MS significantly reduced integrated mineral loss (322.5 [250-580] %vol·µm) and lesion depth (30.1 [15-42.2] µm) compared to P (880 [580-1705]; 58.3 [32.2-88.6] µm; Kruskal-Wallis/Dunn, p≤0.001), while F (587.5 [305-720]; 25.2 [16.5-38.8] µm) did not differ significantly (p>0.05). CONCLUSIONS: Malva sylvestris extract had no antimicrobial effect on Lactobacillus spp. counts, but significantly reduced enamel and dentin demineralization, showing anticaries effect comparable to fluoride. CLINICAL RELEVANCE: Malva sylvestris has demonstrated promising biological activity. This study investigates the antimicrobial efficacy of Malva sylvestris against cariogenic microorganisms in situ. Our findings provide relevant evidence that M. sylvestris exert significant anticaries effects using an in situ model.

Biofilms↗