SMU.940 regulates dextran-dependent aggregation and biofilm formation in Streptococcus mutans

Review on recent advances in the properties, production and applications of microbial dextranases

Dextranase is a type of hydrolase that is responsible for catalyzing the breakdown of high-molecular-weight dextran into low-molecular-weight polysaccharides. This process is called dextranolysis. A select group of bacteria and fungi, including yeasts and likely certain complex eukaryotes, produce dextranase enzymes as extracellular enzymes that are released into the environment. These enzymes join dextran's α-1,6 glycosidic bonds to make glucose, exodextranases, or isomalto-oligosaccharides (endodextranases). Dextranase is an enzyme that has a wide variety of applications, some of which include the sugar business, the production of human plasma replacements, the treatment of dental plaque and its protection, and the creation of human plasma replacements. Because of this, the quantity of studies carried out on worldwide has steadily increased over the course of the past couple of decades. The major focus of this study is on the most current advancements in the production, administration, and properties of microbial dextranases. This will be done throughout the entirety of the review.

vicR overexpression in Streptococcus mutans causes aggregation and affects interspecies competition

Streptococcus mutans is considered to be a major causative agent of dental caries. VicRK is a two-component signal transduction system (TCSTS) of S. mutans, which can regulate the virulence of S. mutans, such as biofilm formation, exopolysaccharide production, acid production, and acid resistance. Meanwhile, it can also regulate the production of mutacins (nlmC) through the TCSTS ComDE. In this study, we found that the vicR-overexpressing strain was more likely to aggregate to form cell clusters, leading to the formation of abnormal biofilm; the overexpression of vicR increased the length of the chain of S. mutans. Furthermore, the expression of the mutacins in the vicR overexpression strain was increased under aerobic conditions. Compared with the control strain and the parental strain, the vicR overexpression strain was more competitive against Streptococcus gordonii. But there was no significant difference against Streptococcus sanguinis. In clinical strains, the expression level of vicR was positively correlated with their competitive ability against S. gordonii. Transcriptional profiling revealed 24 significantly upregulated genes in the vicR-overexpressing strain, including nlmA, nlmB, nlmC, and nlmD encoding mutacins. Electrophoretic mobility shift assays and DNase I footprinting assays confirmed that VicR can directly bind to the promoter sequence of nlmD. Taken together, our findings further demonstrate that VicRK, an important TCSTS of S. mutans, is involved in S. mutans cell morphology and biofilm formation. VicRK regulates the production of more mutacins in S. mutans in response to oxygen stimulation. VicR can bind to the promoter sequence of nlmD, thereby directly regulating the production of mutacins NlmD.

Antibiofilm activity and NMR-based metabolomic characterization of cell-free supernatant of Limosilactobacillus reuteri DSM 17938

The microbial biofilm has been defined as a "key virulence factor" for a multitude of microorganisms associated with chronic infections. Its multifactorial nature and variability, as well as an increase in antimicrobial resistance, suggest the need to identify new compounds as alternatives to the commonly used antimicrobials. The aim of this study was to assess the antibiofilm activity of cell-free supernatant (CFS) and its sub-fractions (SurE 10 K with a molecular weight <10 kDa and SurE with a molecular weight <30 kDa), produced by Limosilactobacillus reuteri DSM 17938, vs. biofilm-producing bacterial species. The minimum inhibitory biofilm concentration (MBIC) and the minimum biofilm eradication concentration (MBEC) were determined via three different methods and an NMR metabolomic analysis of CFS and SurE 10K was performed to identify and quantify several compounds. Finally, the storage stability of these postbiotics was evaluated by a colorimetric assay by analyzing changes in the CIEL*a*b parameters. The CFS showed a promising antibiofilm activity against the biofilm developed by clinically relevant microorganisms. The NMR of CFS and SurE 10K identifies and quantifies several compounds, mainly organic acids and amino acids, with lactate being the most abundant metabolite in all the analyzed samples. The CFS and SurE 10 K were characterized by a similar qualitative profile, with the exception of formate and glycine detected only in the CFS. Finally, the CIEL*a*b parameters assess the better conditions to analyze and use these matrices for the correct preservation of bioactive compounds.

Prospects of microbial polysaccharides-based hybrid constructs for biomimicking applications

Polysaccharides are biobased polymers obtained from renewable sources. They exhibit various interesting features including biocompatibility, biodegradability, and nontoxicity. Microbial polysaccharides are produced by several microorganisms including yeast, fungi, algae, and bacteria. Microbial polysaccharides have gained high importance in biotechnology due to their novel physiochemical characteristics and composition. Among microbial polysaccharides, xanthan, alginate, gellan, and dextran are the most commonly reported polysaccharides for the development of biomimetic materials for biomedical applications including targeted drug delivery, wound healing, and tissue engineering. Several chemical and physical cross-linking reactions are performed to increase their technological and functional properties. Owning to the broad-scale applications of microbial polysaccharides, this review aims to summarize the characteristics with different ways of physical/chemical crosslinking for polysaccharide regulation. Recently, several biopolymers have gained high importance due to their biologically active properties. This will help in the formation of bioactive nutraceuticals and functional foods. This review provides a perspective on microbial polysaccharides, with special emphasis given to applications in promising biosectors and the subsequent advancement on the discovery and development of new polysaccharides for adding new products.

AhrC Negatively Regulates Streptococcus mutans Arginine Biosynthesis

Streptococcus mutans is a primary cariogenic pathogen in humans. Arginine metabolism is required for bacterial growth. In S. mutans, however, the involvement of transcription factors in regulating arginine metabolism is unclear. The purpose of this study was to investigate the function and mechanism of ArgR family transcription factors in S. mutans. Here, we identified an ArgR (arginine repressor) family transcription factor named AhrC, which negatively regulates arginine biosynthesis and biofilm formation in S. mutans. The ahrC in-frame deletion strain exhibited slow growth and significantly increased intracellular arginine content. The strain overexpressing ahrC showed reduced intracellular arginine content, decreased biofilm biomass, reduced production of water-insoluble exopolysaccharides (EPS), and different biofilm structures. Furthermore, global gene expression profiles revealed differential expression levels of 233 genes in the ahrC-deficient strain, among which genes related to arginine biosynthesis (argJ, argB, argC, argD, argF, argG, argH) were significantly upregulated. In the ahrC overexpression strain, there are 89 differentially expressed genes, mostly related to arginine biosynthesis. The conserved DNA patterns bound by AhrC were identified by electrophoretic mobility shift assay (EMSA) and DNase I footprinting. In addition, the analysis of β-galactosidase activity showed that AhrC acted as a negative regulator. Taken together, our findings suggest that AhrC is an important transcription factor that regulates arginine biosynthesis gene expression and biofilm formation in S. mutans. These findings add new aspects to the complexity of regulating the expression of genes involved in arginine biosynthesis and biofilm formation in S. mutans.

IMPORTANCE Arginine metabolism is essential for bacterial growth. The regulation of intracellular arginine metabolism in Streptococcus mutans, one of the major pathogens of dental caries, is unclear. In this study, we found that the transcription factor AhrC can directly and negatively regulate the expression of N-acetyl-gamma-glutamyl-phosphate reductase (argC), thus regulating arginine biosynthesis in S. mutans. In addition, the ahrC overexpression strain exhibited a significant decrease in biofilm and water-insoluble extracellular polysaccharides (EPS). This study adds new support to our understanding of the regulation of intracellular arginine metabolism in S. mutans.

Acid-Induced Self-Catalyzing Platform Based on Dextran-Coated Copper Peroxide Nanoaggregates for Biofilm Treatment

Nanoantibacterial agents based on catalytic activity were limited due to the low levels of endogenous H₂O₂ in the microenvironment of bacterial biofilms. However, the additional H₂O₂ will trigger more side effects to healthy surroundings, which is still a great challenge. Herein, we report an acid-induced self-catalyzing platform based on dextran-coated copper peroxide nanoaggregates (DCPNAs) for antibiofilm and local infection therapy applications. The dextran-functionalized DCPNAs were mediated and conveniently purified via a dextran and ethanol precipitation method, which can also cluster nanodots into nanoaggregates and show good penetrability as well as biocompatibility. Bacterial biofilms were inhibited and destroyed by the reactive oxygen species generated from the Fenton reaction between the Cu²⁺ and H₂O₂ released from DCPNAs in an acidic environment, which did not require additional H₂O₂. As expected, the DCPNAs exhibit low cytotoxicity and excellent acid-induced antibacterial and antibiofilm ability. Moreover, the DCPNAs realized great therapeutic outcomes in the application for in vivo wound healing. The overall excellent properties associated with the DCPNAs highlight that they could be considered as a kind of ideal antimicrobial agents for microbial biofilm infection treatment.

EpsR Negatively Regulates Streptococcus mutans Exopolysaccharide Synthesis

Streptococcus mutans is considered the primary etiological agent of human dental caries. Glucosyltransferases (Gtfs) from S. mutans play important roles in the formation of biofilm matrix and the development of cariogenic oral biofilm. Therefore, Gtfs are considered an important target to prevent the development of dental caries. However, the role of transcription factors in regulating gtf expression is not yet clear. Here, we identify a MarR (multiple antibiotic resistance regulator) family transcription factor named EpsR (exopolysaccharide synthesis regulator), which negatively regulates gtfB expression and exopolysaccharide (EPS) production in S. mutans. The epsR in-frame deletion strain grew slowly, aggregated more easily in the presence of dextran, and displayed different colony morphology and biofilm structure. Notably, epsR deletion resulted in altered 3-dimensional biofilm architecture, increased water-insoluble EPS production, and upregulated GtfB protein content and activity. In addition, global gene expression profiling revealed differences in the expression levels of 69 genes in which gtfB was markedly upregulated. The conserved DNA motif for EpsR binding was determined by electrophoretic mobility shift assay and DNase I footprinting assays. Moreover, analysis of β-galactosidase activity suggested that EpsR acted as a repressor and inhibited gtfB expression. Taken together, our findings indicate that EpsR is an important transcription factor that regulates gtfB expression and EPS production in S. mutans. These results add new aspects to the complexity of regulating the expression of genes involved in the cariogenicity of S. mutans, which might lead to novel strategies to prevent the formation of cariogenic biofilm that may favor diseases.

Effects of nano-hydroxyapatite on the formation of biofilms by Streptococcus mutans in two different media

OBJECTIVES

The aim of this study was to examine the effect of nano-hydroxyapatite (nHA) on biofilm formation by Streptococcus mutans, which is actively involved in the initiation of dental caries.

DESIGN

The effects of nHA on growth and biofilm formation by S. mutans were investigated in two media: a saliva analog medium, basal medium mucin (BMM); and a nutrient-rich medium, brain heart infusion (BHI); in the presence and absence of sucrose.

RESULTS

Sucrose enhanced the growth of S. mutans in both media. In the presence of sucrose, nHA enhanced bacterial growth and biofilm formation more in BMM medium than in BHI. nHA also affected the transcription of glucosyltransferase (gtf) genes and production of polysaccharide differently in the two media. In BHI medium, the transcription of all three gtf genes, coding for enzymes that synthesize soluble and insoluble glucans from sucrose, was increased more than 3-fold by nHA. However, in BMM medium, only the transcription of gtfB and gtfC, coding for insoluble glucans, was substantially enhanced by nHA.

CONCLUSIONS

nHA appeared to enhance biofilm formation by increasing glucosyltransferase transcription, which resulted in an increase in production of insoluble glucans. This effect was influenced by the growth conditions.