Identification and functional analysis of the L-ascorbate-specific enzyme II complex of the phosphotransferase system in Streptococcus mutans

Fructose activates a stress response shared by methylglyoxal and hydrogen peroxide in Streptococcus mutans

Fructose catabolism by Streptococcus mutans is initiated by three phosphotransferase (PTS) transporters yielding fructose-1-phosphate (F-1-P) or fructose-6-phosphate. Deletion of one such F-1-P-generating PTS, fruI, was shown to reduce the cariogenicity of S. mutans in rats fed a high-sucrose diet. Moreover, a recent study linked fructose metabolism in S. mutans to a reactive electrophile species methylglyoxal. Here, we conducted a comparative transcriptomic analysis of S. mutans treated briefly with 50 mM fructose, 50 mM glucose, 5 mM methylglyoxal, or 0.5 mM hydrogen peroxide (H2O2). The results revealed a striking overlap between the fructose and methylglyoxal transcriptomes, totaling 176 genes, 61 of which were also shared with the H2O2 transcriptome. This core of 61 genes encompassed many of the same pathways affected by exposure to low pH or zinc intoxication. Consistent with these findings, fructose negatively impacted the metal homeostasis of a mutant deficient in zinc expulsion and the growth of a mutant of the major oxidative stress regulator SpxA1. Importantly, fructose metabolism lowered culture pH at a faster pace, allowed better survival under acidic and nutrient-depleted conditions, and enhanced the competitiveness of S. mutans against Streptococcus sanguinis, although a moderated level of F-1-P might further boost some of these benefits. Conversely, several commensal streptococcal species displayed a greater sensitivity to fructose that may negatively affect their persistence and competitiveness in dental biofilm. In conclusion, fructose metabolism is integrated into the stress core of S. mutans and regulates critical functions required for survival and its ability to induce dysbiosis in the oral cavity.IMPORTANCEFructose is a common monosaccharide in the biosphere, yet its overconsumption has been linked to various health problems in humans including insulin resistance, obesity, diabetes, non-alcoholic liver diseases, and even cancer. These effects are in large part attributable to the unique biochemical characteristics and metabolic responses associated with the degradation of fructose. Yet, an understanding of the effects of fructose on the physiology of bacteria and its implications for the human microbiome is severely lacking. Here, we performed a series of analyses on the gene regulation of a dental pathogen Streptococcus mutans by exposing it to fructose and other important stress agents. Further supported by growth, persistence, and competition assays, our findings revealed the ability of fructose to activate a set of stress-related functions that may prove critical to the ability of the bacterium to persist and cause diseases both within and without the oral cavity.

FRUCTOSE ACTIVATES A STRESS RESPONSE SHARED BY METHYLGLYOXAL AND HYDROGEN PEROXIDE IN STREPTOCOCCUS MUTANS

Fructose catabolism by Streptococcus mutans is initiated by three PTS transporters yielding either fructose-1-phoshate (F-1-P) or fructose-6-phosphate (F-6-P). Deletion of one such F-1-P-generating PTS, fruI, has been shown to reduce the cariogenicity of S. mutans in rats fed a high-sucrose diet. Moreover, a recent study linked fructose metabolism in S. mutans to a reactive electrophile species (RES) methylglyoxal. Here, we conducted a comparative transcriptomic analysis of exponentially grown S. mutans shocked with 50 mM fructose, 50 mM glucose, 5 mM methylglyoxal, or 0.5 mM hydrogen peroxide (H2O2). The results revealed a striking overlap between the fructose and methylglyoxal transcriptomes, totaling 176 genes, 61 of which were also shared with the H2O2 transcriptome. This core of 61 genes encompassed many of the same pathways affected by exposure to low pH or zinc intoxication. Consistent with these findings, fructose negatively impacted metal homeostasis of a mutant deficient in zinc expulsion and the growth of a mutant of the major oxidative stress regulator SpxA1. We further demonstrated the induction of the superoxide dismutase (sodA) and the fruRKI operon by different levels of fructose. Finally, fructose metabolism lowered culture pH at a faster pace, allowed better survival under acidic and nutrient-depleted conditions, and enhanced the competitiveness of S. mutans against Streptococcus sanguinis, although a moderated level of F-1-P might further boost some of these benefits. In conclusion, fructose metabolism is integrated into the stress core of S. mutans and regulates critical functions required for survival in both the oral cavity and during systemic infections. Importance. Fructose is a common monosaccharide in the biosphere, yet its overconsumption has been linked to various health problems in humans including insulin resistance, obesity, diabetes, and non-alcoholic liver diseases. These effects are in large part attributed to the unique biochemical characteristics and metabolic responses associated with the degradation of fructose. Yet, an understanding of the effects of fructose on the physiology of bacteria and its implications to the human microbiome is severely lacking. Here we performed a series of analyses on the gene regulation of a dental pathogen Streptococcus mutans by exposing it to fructose and other important stress agents. Further supported by growth, persistence, and competition assays, our findings revealed the ability of fructose to activate a set of cellular functions that may prove critical to the ability of the bacterium to persist and cause diseases both within and without of the oral cavity.

Decoding gene expression dynamics in planktonic and biofilm cells of Streptococcus mutans: regulation and role of mutanofactin genes in biofilm formation

Introduction

Dental caries is the most prevalent chronic infectious disease globally, with Streptococcus mutans recognized as a primary causative agent due to its acidogenicity and robust biofilm-forming ability. In S. mutans biofilm formation, the role of autoinducers has been extensively studied, while the influence of other small molecules remains largely unexplored. Mutanofactins, a class of polyketide/non-ribosomal lipopeptide secondary metabolites, are emerging as potential modulators of S. mutans biofilm development.

Methods

Transcriptomic analysis was conducted to examine gene expression patterns in S. mutans NMT4863 across distinct growth phases and lifestyles, aiming to identify metabolic factors influencing biofilm formation. Transcriptomic profiles were compared between cells in early-, mid-, and late-exponential-, and stationary phase, as well as between planktonic and biofilm cells. Differentially expressed genes were identified, and pathway analyses revealed significant alterations in key metabolic and regulatory pathways. Specifically, the biosynthetic mutanofactin gene cluster was analyzed via quantitative real-time polymerase chain reaction.

Results

Several genes and operons were differentially expressed across the tested growth phases, with 1,095 genes showing differential expression between stationary-phase, planktonic and biofilm cells. Pathway analysis revealed significant changes in ascorbate metabolism, carbohydrate utilization and transport systems, lipoic acid metabolism, bacterial toxin pathways, two-component regulatory systems, and secondary metabolite biosynthesis. Notably, expression of the muf gene cluster, was elevated in early exponential-phase cells relative to stationary-phase cells. Additionally, the mufCDEFGHIJ genes were identified as components of a single transcriptional unit (muf operon). MufC, a transcriptional regulator of the TetR/AcrR-family, acts as a positive regulator of the muf operon in strain NMT4863. Bioinformatic analysis pinpointed a 20-bp regulatory sequence in the muf operon promoter region (5'-AAATGAGCTATAATTCATTT-3'). Interestingly, the muf operon was found to be significantly downregulated in biofilm cells.

Conclusion

This study provides key insights into gene expression dynamics that drive biofilm formation in S. mutans NMT4863, with a particular emphasis on the role of the muf operon. This operon is governed by the TetR/AcrR-family regulator MufC and plays a central role in biofilm development, offering a novel perspective on the molecular basis of S. mutans biofilm formation and resilience.

Multi-omics analysis reveals genes and metabolites involved in Streptococcus suis biofilm formation

BACKGROUND

Streptococcus suis is an important zoonotic pathogen. Biofilm formation largely explains the difficulty in preventing and controlling S. suis. However, little is known about the molecular mechanism of S. suis biofilm formation.

RESULTS

In this study, transcriptomic and metabolomic analyses of S. suis in biofilm and planktonic states were performed to identify key genes and metabolites involved in biofilm formation. A total of 789 differential genes and 365 differential metabolites were identified. By integrating transcriptomics and metabolomics, five main metabolic pathways were identified, including amino acid pathway, nucleotide metabolism pathway, carbon metabolism pathway, vitamin and cofactor metabolism pathway, and aminoacyl-tRNA biosynthesis metabolic pathway.

CONCLUSIONS

These results provide new insights for exploring the molecular mechanism of S. suis biofilm formation.

EⅡB Mutation Reduces the Pathogenicity of Listeria monocytogenes by Negatively Regulating Biofilm Formation Ability, Infective Capacity, and Virulence Gene Expression

To explore the role of the membrane permease ⅡB (EⅡB) gene of Listeria pathogenicity island 4 (LIPI-4) in the virulence of Listeria monocytogenes, both an EⅡB deletion strain (∆EⅡB) and a complemented strain were constructed. In vitro experiments demonstrated that EⅡB deletion affected the biofilm formation ability of the wild-type strain (Lm928). Moreover, this deletion decreased the intracellular proliferation abilities of L. monocytogenes. Mice infected with ∆EⅡB survived longer and experienced less weight loss on days 1, 2, and 3 post-infection. The bacterial load in the liver tissue of ∆EⅡB-infected mice was significantly reduced, and a considerable decrease in the blood levels of inflammatory cytokines IL-β, IL-6, IL-10, and TNF-α were observed. Following EⅡB deletion, 65% (13/20) of genes were downregulated, 25% (5/20) were upregulated, and 10% (2/20) showed no change. These findings suggest that EⅡB deletion may reduce both the in vivo and in vitro virulence levels as well as the biofilm formation ability of Lm928 by downregulating the transcription levels of genes associated with virulence and biofilm formation. These findings provide a foundation for further examining the pathogenic mechanisms of LIPI-4 and EⅡB in L. monocytogenes.

Transposon library screening to identify genes with a potential role in Streptococcus suis biofilm formation

Background: Biofilm formation is considered to be one of reasons for difficulty in the prevention and control of Streptococcus suis. Aims: To explore the potential genes involved in the biofilm formation of S. suis. Methods: Transposon mutagenesis technology was used to screen biofilm-defective strains of S. suis, and the potential genes related to biofilm were identified. Results: A total of 19 genes were identified that were involved in bacterial metabolism, peptidoglycan-binding protein, cell wall synthesis, ABC transporters, and so on. Conclusion: This study constructed 979 transposon mutation libraries of S. suis. A total of 19 gene loci related to the formation of S. suis biofilm were identified, providing a reference for exploring the mechanism of S. suis biofilm formation in the future.

Genomic and metabolic insights into the first host-associated isolate of Psychrilyobacter

Although gut bacteria are vital to their hosts, few studies have focused on marine animals. Psychrilyobacter is frequently related to various marine animals, but its interaction with host remains unknown due to the lack of host-associated isolate or genomic information. Here, we combined cultivation-independent and cultivation-dependent methods to uncover the potential roles of Psychrilyobacter in the host abalone. The high-throughput sequencing and literature compiling results indicated that Psychrilyobacter is widely distributed in marine and terrestrial ecosystems with both host-associated and free-living lifestyles, but with a strong niche preference in the guts of marine invertebrates, especially abalone. By in vitro enrichment that mimicked the gut inner environment, the first host-related pure culture of Psychrilyobacter was isolated from the abalone intestine. Phylogenetic, physiological, and biochemical characterizations suggested that it represents a novel species named Psychrilyobacter haliotis B1. Carbohydrate utilization experiments and genomic evidence indicated that B1 can utilize diverse host-food-related monosaccharides and disaccharides but not polysaccharides, implying its potential role in the downstream fermentation instead of the upstream food degradation in the gut. Particularly, this strain showed potential to colonize the gut and benefit the host via different strategies, such as the short-chain fatty acids generation by fermenting peptides and/or amino acids, and the putative production of diverse vitamins and antibiotics to support the host growth and antipathogenicity. To our knowledge, strain B1 represents the first host-related pure culture of Psychrilyobacter; genomic and metabolic evidence showed some beneficial characteristics of the dominant gut anaerobe to the host. IMPORTANCE Psychrilyobacter is a globally distributed bacterial genus and with an inhabiting preference for guts of marine invertebrates. Due to the difficulty of cultivation and the limited genomic information, its role in host remains largely unknown. We isolated the first host-associated Psychrilyobacter species from abalone gut and uncovered its functional potential to the host through different mechanisms. Our findings provide some insights into the understanding of host-microbe interactions on a core taxon with the marine invertebrates, and the isolate may have an application potential in the protection of marine animals.

Roles of adenine methylation in the physiology of Lacticaseibacillus paracasei

Lacticaseibacillus paracasei is an economically important bacterial species, used in the food industry and as a probiotic. Here, we investigate the roles of N6-methyladenine (6mA) modification in L. paracasei using multi-omics and high-throughput chromosome conformation capture (Hi-C) analyses. The distribution of 6mA-modified sites varies across the genomes of 28 strains, and appears to be enriched near genes involved in carbohydrate metabolism. A pglX mutant, defective in 6mA modification, shows transcriptomic alterations but only modest changes in growth and genomic spatial organization.

Glucose Phosphotransferase System Modulates Pyruvate Metabolism, Bacterial Fitness, and Microbial Ecology in Oral Streptococci

Spontaneous mutants with defects in the primary glucose phosphotransferase permease (manLMNO) of Streptococcus sanguinis SK36 showed enhanced fitness at low pH. Transcriptomics and metabolomics with a manL deletion mutant (SK36/manL) revealed redirection of pyruvate to production of acetate and formate, rather than lactate. These observations were consistent with measurements of decreased lactic acid accumulation and increased excretion of acetate, formate, pyruvate, and H2O2. Genes showing increased expression in SK36/manL included those encoding carbohydrate transporters, extracellular glycosidases, intracellular polysaccharide metabolism, and arginine deiminase and pathways for metabolism of acetoin, ethanolamine, ascorbate, and formate, along with genes required for membrane biosynthesis and adhesion. Streptococcus mutans UA159 persisted much better in biofilm cocultures with SK36/manL than with SK36, an effect that was further enhanced by culturing the biofilms anaerobically but dampened by adding arginine to the medium. We posited that the enhanced persistence of S. mutans with SK36/manL was in part due to excess excretion of pyruvate by the latter, as addition of pyruvate to S. mutans-S. sanguinis cocultures increased the proportions of UA159 in the biofilms. Reducing the buffer capacity or increasing the concentration of glucose benefited UA159 when cocultured with SK36, but not with SK36/manL, likely due to the altered metabolism and enhanced acid tolerance of the mutant. When manL was deleted in S. mutans or Streptococcus gordonii, the mutants presented altered fitness characteristics. Our study demonstrated that phosphotransferase system (PTS)-dependent modulation of central metabolism can profoundly affect streptococcal fitness and metabolic interactions, revealing another dimension in commensal-pathogen relationships influencing dental caries development. IMPORTANCE Dental caries is underpinned by a dysbiotic microbiome and increased acid production. As beneficial bacteria that can antagonize oral pathobionts, oral streptococci such as S. sanguinis and S. gordonii can ferment many carbohydrates, despite their relative sensitivity to low pH. We characterized the molecular basis for why mutants of glucose transporter ManLMNO of S. sanguinis showed enhanced production of hydrogen peroxide and ammonia and improved persistence under acidic conditions. A metabolic shift involving more than 300 genes required for carbohydrate transport, energy production, and envelope biogenesis was observed. Significantly, manL mutants engineered in three different oral streptococci displayed altered capacities for acid production and interspecies antagonism, highlighting the potential for targeting the glucose-PTS to modulate the pathogenicity of oral biofilms.

Reconstruction of a Cofactor Self-Sufficient Whole-Cell Biocatalyst System for Efficient Biosynthesis of Allitol from d-Glucose

The combined catalysis of glucose isomerase (GI), d-psicose 3-epimerase (DPEase), ribitol dehydrogenase (RDH), and formate dehydrogenase (FDH) provides a convenient route for the biosynthesis of allitol from d-glucose; however, the low catalytic efficiency restricts its industrial applications. Here, the supplementation of 0.32 g/L NAD⁺ significantly promoted the cell catalytic activity by 1.18-fold, suggesting that the insufficient intracellular NAD(H) content was a limiting factor in allitol production. Glucose dehydrogenase (GDH) with 18.13-fold higher activity than FDH was used for reconstructing a cofactor self-sufficient system, which was combined with the overexpression of the rate-limiting genes involved in NAD⁺ salvage metabolic flow to expand the available intracellular NAD(H) pool. Then, the multienzyme self-assembly system with SpyTag and SpyCatcher effectively channeled intermediates, leading to an 81.1% increase in allitol titer to 15.03 g/L from 25 g/L d-glucose. This study provided a facilitated strategy for large-scale and efficient biosynthesis of allitol from a low-cost substrate.

Transcriptional regulator XtgS is involved in iron transition and attenuates the virulence of Streptococcus agalactiae

Streptococcus agalactiae (GBS) is an important pathogen that has increasingly received attention for its role in invasive infections and its broad host range. Research on the regulation of gene expression could illuminate GBS pathogenesis. We previously identified a novel transcriptional regulator XtgS, which is a negative regulator of GBS pathogenicity. Here, we demonstrate that XtgS overexpression significantly attenuated GBS virulence in zebrafish infection tests, and XtgS indirectly downregulated the transcription of two iron transport systems based on the results of transcriptomic analysis, electrophoretic mobility shift assays (EMSAs) and lacZ fusion assays. Subsequent studies verified that the inactivation of iron transport system 1 resulted in GBS excessive iron accumulation and attenuated virulence. Thus, we infer that the downregulation of iron transport system 1 caused by XtgS overexpression probably attenuates bacterial virulence, which partially clarifies the mechanism by which XtgS alleviates the pathogenesis. These findings provide new insights into the relationship between exogenous transcriptional regulation and bacterial virulence.

Functional Characterization of c-di-GMP Signaling-Related Genes in the Probiotic Lactobacillus acidophilus

The bacterial second messenger cyclic diguanylate monophosphate (c-di-GMP) regulates a series of cellular functions, including biofilm formation, motility, virulence, and other processes. In this study, we confirmed the presence of several c-di-GMP related genes and evaluated their activities and functions in Lactobacillus species. Bioinformatic and biochemical analyses revealed that Lactobacillus acidophilus La-14 have an active c-di-GMP phosphodiesterase (PdeA) that may act in the metabolic cycle of c-di-GMP. A GGDEF protein (DgcA) induced two c-di-GMP-dependent phenotypes (low motility and high production of curli fimbriae) in Escherichia coli by heterologously expressed in vivo but showed no diguanylate cyclases activity in vitro while in the expression without the N-terminal transmembrane domain. The degenerated EAL-domain protein (PdeB), encoded by the last gene in the gts operon, serve as a c-di-GMP receptor which may be associated with exopolysaccharide (EPS) synthesis in L. acidophilus. Heterologously expressed GtsA and GtsB, encoded by the gts operon, stimulated EPS and biofilm formation in E. coli BL21. Constitutive expression in L. acidophilus revealed that a high concentration of intracellular DgcA levels increased EPS production in L. acidophilus and enhanced the co-aggregation ability with E. coli MG1655, which may be beneficial to the probiotic properties of Lactobacillus species. Our study imply that the c-di-GMP metabolism-related genes, in L. acidophilus, work jointly to regulate its functions in EPS formation and co-aggregation.

[Role of SMU.2055 gene in regulating acid resistance of Streptococcus mutans UA159]

OBJECTIVE

To evaluate the effect of SMU.2055 gene on acid resistance of Streptococcus mutans.

METHODS

A SMU.2055-dificient mutant strain of S. mutans was constructed using homologous recombination technique. The growth of the wild-type and mutant strains was monitored in both normal and acidic conditions. The lethal pH level, glycolysis, proton permeability, cell permeability and biofilm formation of the two strains were compared.

RESULTS

PCR and sequence analyses verified the successful construction of the SMU.2055-dificient mutant strain. The growth and biofilm formation capacity of the mutant strain were obviously lowered in both normal and acidic conditions. The mutant strain also showed increased lethal pH level, proton permeability, and cell permeability with impaired H⁺-ATPase activity in acidic conditions, but its minimum glycolytic pH remained unaffected.

CONCLUSION

The SMU.2055-deficient S. mutans mutant exhibits a lowered acid resistance, which affects the growth, lethal pH, proton permeability, H⁺-ATPase activity, cell permeability and biofilm formation but not the minimum glycolytic pH of the mutant strain.

[Role of SMU.2055 gene in regulating acid resistance of Streptococcus mutans UA159]

OBJECTIVE

To evaluate the effect of SMU.2055 gene on acid resistance of Streptococcus mutans.

METHODS

A SMU.2055-dificient mutant strain of S. mutans was constructed using homologous recombination technique. The growth of the wild-type and mutant strains was monitored in both normal and acidic conditions. The lethal pH level, glycolysis, proton permeability, cell permeability and biofilm formation of the two strains were compared.

RESULTS

PCR and sequence analyses verified the successful construction of the SMU.2055-dificient mutant strain. The growth and biofilm formation capacity of the mutant strain were obviously lowered in both normal and acidic conditions. The mutant strain also showed increased lethal pH level, proton permeability, and cell permeability with impaired H+-ATPase activity in acidic conditions, but its minimum glycolytic pH remained unaffected.

CONCLUSION

The SMU.2055-deficient S. mutans mutant exhibits a lowered acid resistance, which affects the growth, lethal pH, proton permeability, H+-ATPase activity, cell permeability and biofilm formation but not the minimum glycolytic pH of the mutant strain.

In silico search of inhibitors of Streptococcus mutans for the control of dental plaque

Biofilm is an extremely complex microbial community arranged in a matrix of polysaccharides and attached to a substrate. Its development is crucial in the pathophysiology of oral infections like dental caries, as well as in periodontal, pulp, and periapical diseases. Streptococcus mutans is one of the most effective microorganisms in lactic acid production of the dental biofilm. Identifying essential Streptococcus mutans proteins using bioinformatics methods helps to search for alternative therapies. To this end, the bacterial genomes of several Streptococcus mutans strains and representative strains of other cariogenic and non-cariogenic bacteria were analysed by identifying pathogenicity islands and alignments with other bacteria, and by detecting the exclusive genes of cariogenic species in comparison to the non-pathogenic ones. This study used tools for orthology prediction such as BLAST and OrthoMCL, as well as the server IslandViewer for the detection of pathogenicity islands. In addition, the potential interactome of Streptococcus mutans was rebuilt by comparing it to interologues of other species phylogenetically close to or associated with cariogenicity. This protocol yielded a final list of 20 proteins related to potentially virulent factors that can be used as therapeutic targets in future analyses. The EIIA and EIIC enzymatic subunits of the phosphotransferase system (PTS) were prioritized, as well as the pyruvate kinase enzyme, which are directly involved in the metabolism of carbohydrates and in obtaining the necessary energy for the microorganism's survival. These results will guide a subsequent experimental trial to develop new, safe, and effective molecules in the treatment of dental caries.

[Role of SMU.2055 gene in cariogenic capacity of Streptococcus mutans]

OBJECTIVE

To construct a SMU.2055-dificient mutant strain of Streptococcus mutans (S. mutans) and evaluate its cariogenic capacity in comparison with wild-type S. mutans.

METHODS

The SMU.2055-dificient mutant strain of S. mutans was constructed using homologous recombination technique and observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The absorbance at 600 nm and pH values of the wild-type and mutant strains were monitored to evaluate their growth and acid production. After acid adaption, the two strains were challenged with acid shock and their survival rates were determined.

RESULTS

PCR and sequence analyses verified the successful construction of the SMU.2055-dificient mutant strain. Observation with SEM revealed obvious changes in the morphology of the mutant strain, which showed reduced irregular substances between the individual bacteria as compared with the wild-type strain. TEM revealed major alterations in the cellular architecture of the mutant strain with blurry cell membrane and disruption of the membrane integrity. The growth capacity of the mutant strain decreased in both normal and acidic conditions but its acid production capacity remained unaffected.

CONCLUSION

SMU.2055 gene is associated with morphology maintenance, growth capacity and acid resistance of S. mutans but is not related to the acid production capacity of the bacterium.

[Role of SMU.2055 gene in cariogenic capacity of Streptococcus mutans]

OBJECTIVE

To construct a SMU.2055-dificient mutant strain of Streptococcus mutans (S. mutans) and evaluate its cariogenic capacity in comparison with wild-type S. mutans.

METHODS

The SMU.2055-dificient mutant strain of S. mutans was constructed using homologous recombination technique and observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The absorbance at 600 nm and pH values of the wild-type and mutant strains were monitored to evaluate their growth and acid production. After acid adaption, the two strains were challenged with acid shock and their survival rates were determined.

RESULTS

PCR and sequence analyses verified the successful construction of the SMU.2055-dificient mutant strain. Observation with SEM revealed obvious changes in the morphology of the mutant strain, which showed reduced irregular substances between the individual bacteria as compared with the wild-type strain. TEM revealed major alterations in the cellular architecture of the mutant strain with blurry cell membrane and disruption of the membrane integrity. The growth capacity of the mutant strain decreased in both normal and acidic conditions but its acid production capacity remained unaffected.

CONCLUSION

SMU.2055 gene is associated with morphology maintenance, growth capacity and acid resistance of S. mutans but is not related to the acid production capacity of the bacterium.