Inhibitory effect of Bacillus velezensis on biofilm formation by Streptococcus mutans

Biocontrol manufacturing and agricultural applications of Bacillus velezensis

Many microorganisms have been reported as bioagents for producing ecofriendly, cost-effective, and safe products. Some Bacillus species of bacteria can be used in agricultural applications. Bacillus velezensis in particular has shown promising results for controlling destructive phytopathogens and in biofungicide manufacturing. Some B. velezensis strains can promote plant growth and display antibiotic activities against plant pathogen agents. In this review, we focus on the often-overlooked potential properties of B. velezensis as a bioagent for applications that will extend beyond the traditional agricultural uses. We delve into its versatility and future prospects, the challenges such uses may encounter, and some drawbacks associated with B. velezensis-based products.

Studies on 1-deoxynojirimycin biosynthesis in mulberry (Morus alba L.) seeds through comparative transcriptomics

Mulberry (Morus alba L.) plants are rich in 1-deoxynojirimycin (DNJ), which is a potential α-glucosidase inhibitor exhibiting various physiological activities. Compared to other tissues, Morus alba L. seeds contain the highest DNJ content, however, the DNJ biosynthesis mechanisms are unclear. In this study, we examined fruits of 27 mulberry varieties and found that variety MS02 had the highest DNJ levels (22.28 mg/g), whereas variety MS15 contained the lowest DNJ levels (0.37 mg/g). Through comparative transcriptomics, 1,719 differentially expressed genes (DEGs) were identified, 1,170 of which were upregulated, and 549 were downregulated in MS02 compared to MS15. DEGs were associated with cellular processes, metabolic processes, and catalytic activity. Specifically, nine DEGs were identified to be involved in alkaloid biosynthesis pathways, according to Kyoto Encyclopaedia of Genes and Genomes enrichment analysis, and four enzymes, i.e. polyphenol oxidase, tyrosine aminotransferase, aromatic-L-amino-acid decarboxylase, and tropinone reductase, are proposed to play important roles in DNJ biosynthesis. In conclusion, DNJ biosynthesis in mulberry seeds appears to be mediated by upregulation of polyphenol oxidase, tyrosine aminotransferase, aromatic-L-amino-acid decarboxylase, and tropinone reductase.

Production of Lipopeptides from Bacillus velezensis BVQ121 and Their Application in Chitosan Antibacterial Coating

The extracellular substance of Bacillus has antibacterial effects inhibiting multiple foodborne pathogens and plays important roles in food production. This study found one Bacillus velezensis BVQ121 strain producing antibacterial lipopeptides (BVAL). After optimization of the fermentation conditions, the BVAL yield was the highest at 1.316 ± 0.03 g/L in reality with the initial pH 6.0, temperature 31 °C, and shaker speed 238 rpm when the optimal nitrogen and carbon sources were used in Landy medium for fermentation. The antibacterial components were identified as iturin, surfactin, and fengycin by HPLC and MALDI-TOF-MS. The MIC was at 2 mg/mL and MBC was at 5 mg/mL. The 6% weight ratio of nanocellulose dosage in chitosan solution could improve the tensile length and strength of the film, and the antibacterial performance was enhanced by the addition of BVAL. The addition of BVAL had no effect on the color and ductility of the film and improved its antibacterial effect. The shelf life of pigeon eggs can be extended by more than 10 days to resist bacterial infections after coating with the chitosan-nanocellulose-BVAL film solution.

Targeted Isolation of Antibiofilm Compounds from Halophytic Endophyte Bacillus velezensis 7NPB-3B Using LC-HR-MS-Based Metabolomics

The discovery of new natural products has become more challenging because of the re-isolation of compounds and the lack of new sources. Microbes dwelling in extreme conditions of high salinity and temperature are huge prospects for interesting natural metabolites. In this study, the endophytic bacteria Bacillus velezensis 7NPB-3B isolated from the halophyte Salicornia brachiata was screened for its biofilm inhibition against methicillin-resistant Staphylococcus aureus (MRSA). The fractionation of the crude extract was guided by bioassay and LC-HRMS-based metabolomics using multivariate analysis. The 37 fractions obtained by high-throughput chromatography were dereplicated using an in-house MS-Excel macro coupled with the Dictionary of Natural Products database. Successive bioactivity-guided separation yielded one novel compound (1), a diketopiperazine (m/z 469.258 [M - H]-) with an attached saturated decanoic acid chain, and four known compounds (2-5). The compounds were identified based on 1D- and 2D-NMR and mass spectrometry. Compounds 1 and 5 exhibited excellent biofilm inhibition properties of >90% against the MRSA pathogen at minimum inhibition concentrations of 25 and 35 µg/mL, respectively. The investigation resulted in the isolation of a novel diketopiperazine from a bacterial endophyte of an untapped plant using an omics approach.

Probiotic Lactobacillus plantarum Ln4 Showing Antimicrobial and Antibiofilm Effect against Streptococcus mutans KCTC 5124 Causing Dental Caries

Dental caries has known as an infectious disease that is considered a serious global public health problem. Recently, report indicate that probiotics play a vital role in maintaining oral health. Therefore, this study aimed to evaluate the prevention effects of Lactobacillus plantarum Ln4 against dental infection by the pathogenic bacterium Streptococcus mutans KCTC 5124 through biofilm formation inhibition. To evaluate such prevention effects against S. mutans KCTC 5124, antimicrobial activity, auto-aggregation, co-aggregation, cell surface hydrophobicity, total exopolysaccharide (EPS) production rate, and biofilm formation were analyzed. Results showed that L. plantarum Ln4 showed higher antimicrobial activity than L. rhamnosus GG (LGG). In the group treated with L. plantarum Ln4, the co-aggregation (58.85%), cell surface hydrophobicity (16.75%), and EPS production rate (73.29%) values were lower than those of LGG and the negative control. Additionally, crystal violet staining and confocal laser scanning microscopy (CLSM) revealed that L. plantarum Ln4 effectively inhibited biofilm formation in S. mutans KCTC 5124. Therefore, L. plantarum Ln4 could be used in the industry as a probiotics to prevent and improve oral health.

Anti-bacterial, anti-biofilm and anti-quorum sensing activities of honey: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Man has used honey to treat diseases since ancient times, perhaps even before the history of medicine itself. Several civilizations have utilized natural honey as a functional and therapeutic food to ward off infections. Recently, researchers worldwide have been focusing on the antibacterial effects of natural honey against antibiotic-resistant bacteria.

AIM OF THE STUDY

This review aims to summarize research on the use of honey properties and constituents with their anti-bacterial, anti-biofilm, and anti-quorum sensing mechanisms of action. Further, honey's bacterial products, including probiotic organisms and antibacterial agents which are produced to curb the growth of other competitor microorganisms is addressed.

MATERIALS AND METHODS

In this review, we have provided a comprehensive overview of the antibacterial, anti-biofilm, and anti-quorum sensing activities of honey and their mechanisms of action. Furthermore, the review addressed the effects of antibacterial agents of honey from bacterial origin. Relevant information on the antibacterial activity of honey was obtained from scientific online databases such as Web of Science, Google Scholar, ScienceDirect, and PubMed.

RESULTS

Honey's antibacterial, anti-biofilm, and anti-quorum sensing activities are mostly attributed to four key components: hydrogen peroxide, methylglyoxal, bee defensin-1, and phenolic compounds. The performance of bacteria can be altered by honey components, which impact their cell cycle and cell morphology. To the best of our knowledge, this is the first review that specifically summarizes every phenolic compound identified in honey along with their potential antibacterial mechanisms of action. Furthermore, certain strains of beneficial lactic acid bacteria such as Bifidobacterium, Fructobacillus, and Lactobacillaceae, as well as Bacillus species can survive and even grow in honey, making it a potential delivery system for these agents.

CONCLUSION

Honey could be regarded as one of the best complementary and alternative medicines. The data presented in this review will enhance our knowledge of some of honey's therapeutic properties as well as its antibacterial activities.

Alleviation of dental caries by use of isolated potential probiotic and its characterization

Streptococcus mutans plays a major role in biofilm formation and pathogenic bacterial adhesion. Here we investigated the abilities of our isolates from diverse conventional sources to characterize the beneficial bacteria for inhibition of S. mutans. Enterobacter cloacae PS-74, a beneficial bacteria isolated from yoghurt, is gram negative, rod shaped, and resistant to acid, bile salt, and amylase. PS-74 cell-free supernatants (CFS) demonstrated highest zone of inhibition of 29 ± 1.7 mm. Further, the minimum inhibitory concentration (MIC) value of CFS PS-74 was recorded to be 10 μL and its minimum bactericidal concentration (MBC) value was found to be 15μL which led to 99.9% log reduction of S. mutans. Moreover, the biofilm formation was reduced by 84.91% at MIC15 of CFS PS-74 which alleviate the dental caries formation by S. mutans. This is the first report on E. cloacae PS-74, which was studied for its probiotic properties to inhibit S. mutans MTCC-890 due to the production of organic acids and employed in oral treatment.

Inhibition of heterotrophic bacterial biofilm in the soil ferrosphere by Streptomyces spp. and Bacillus velezensis

The soil microbiome is involved in the processes of microbial corrosion, in particular, by the formation of biofilm. It has been proposed that an environmentally friendly solution to this corrosion might be through biological control. Bacillus velezensis NUChC C2b, Streptomyces gardneri ChNPU F3 and S. canus NUChC F2 were investigated as potentially 'green' biocides to prevent attachment to glass as a model surface and the formation of heterotrophic bacterial biofilm which participates in the corrosion process. Results showed high antagonistic and antibiofilm properties of S. gardneri ChNPU F3; which may be related to the formation of secondary antimicrobial metabolites by this strain. B. velezensis NUChC C2b and S. gardneri ChNPU F3 could be incorporated into green biocides - as components of antibiofilm agents that will protect material from bacterial corrosion or as agents that will prevent historical heritage damage.

Antibacterial and Antibiofilm Effect of Cell-Free Supernatant of Lactobacillus brevis KCCM 202399 Isolated from Korean Fermented Food against Streptococcus mutans KCTC 5458

This study aims to determine the antibiofilm effect of cell-free supernatant (CFS) of Lactobacillus brevis strains against Streptococcus mutans strains. To study the antibiofilm mechanism against S. mutans strains, antibacterial effects, cell surface properties (auto-aggregation and cell surface hydrophobicity), exopolysaccharide (EPS) production, and morphological changes were examined. The antibiofilm effect of L. brevis KCCM 202399 CFS as morphological changes were evaluated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), compared with the control treatment. Among the L. brevis strains, L. brevis KCCM 202399 showed the highest antibiofilm effect on S. mutans KCTC 5458. The antibacterial effect of L. brevis KCCM 202399 against S. mutans KCTC 5458 was investigated using the deferred method (16.00 mm). The minimum inhibitory concentration of L. brevis KCCM 202399 against S. mutans KCTC 5458 was 25.00%. Compared with the control treatment, L. brevis KCCM 202399 CFS inhibited the bacterial adhesion of S. mutans KCTC 5458 by decreasing auto-aggregation, cell surface hydrophobicity, and EPS production (45.91%, 40.51%, and 67.44%, respectively). L. brevis KCCM 202399 CFS inhibited and eradicated the S. mutans KCTC 5458 biofilm. Therefore, these results suggest that L. brevis KCCM 202399 CFS may be used to develop oral health in the probiotic industry.

Bacillus subtilis natto Derivatives Inhibit Enterococcal Biofilm Formation via Restructuring of the Cell Envelope

Enterococcus faecalis is considered a leading cause of hospital-acquired infections. Treatment of these infections has become a major challenge for clinicians because some E. faecalis strains are resistant to multiple clinically used antibiotics. Moreover, the presence of E. faecalis biofilms can make infections with E. faecalis more difficult to eradicate with current antibiotic therapies. Thus, our aim in this study was to investigate the effects of probiotic derivatives against E. faecalis biofilm formation. Bacillus subtilis natto is a probiotic strain isolated from Japanese fermented soybean foods, and its culture fluid potently inhibited adherence to Caco-2 cell monolayers, aggregation, and biofilm production without inhibiting the growth of E. faecalis. An apparent decrease in the thickness of E. faecalis biofilms was observed through confocal laser scanning microscopy. In addition, exopolysaccharide synthesis in E. faecalis biofilms was reduced by B. subtilis natto culture fluid treatment. Carbohydrate composition analysis also showed that carbohydrates in the E. faecalis cell envelope were restructured. Furthermore, transcriptome sequencing revealed that the culture fluid of B. subtilis natto downregulated the transcription of genes involved in the WalK/WalR two-component system, peptidoglycan biosynthesis and membrane glycolipid biosynthesis, which are all crucial for E. faecalis cell envelope synthesis and biofilm formation. Collectively, our work shows that some derivatives present in the culture fluid of B. subtilis natto may be useful for controlling E. faecalis biofilms.

Acetylation of glucosyltransferases regulates Streptococcus mutans biofilm formation and virulence

Lysine acetylation is a frequently occurring post-translational modification (PTM), emerging as an important metabolic regulatory mechanism in prokaryotes. This process is achieved enzymatically by the protein acetyltransferase (KAT) to specifically transfer the acetyl group, or non-enzymatically by direct intermediates (acetyl phosphate or acetyl-CoA). Although lysine acetylation modification of glucosyltransferases (Gtfs), the important virulence factor in Streptococcus mutans, was reported in our previous study, the KAT has not been identified. Here, we believe that the KAT ActG can acetylate Gtfs in the enzymatic mechanism. By overexpressing 15 KATs in S. mutans, the synthesized water-insoluble extracellular polysaccharides (EPS) and biofilm biomass were measured, and KAT (actG) was identified. The in-frame deletion mutant of actG was constructed to validate the function of actG. The results showed that actG could negatively regulate the water-insoluble EPS synthesis and biofilm formation. We used mass spectrometry (MS) to identify GtfB and GtfC as the possible substrates of ActG. This was also demonstrated by in vitro acetylation assays, indicating that ActG could increase the acetylation levels of GtfB and GtfC enzymatically and decrease their activities. We further found that the expression level of actG in part explained the virulence differences in clinically isolated strains. Moreover, overexpression of actG in S. mutans attenuated its cariogenicity in the rat caries model. Taken together, our study demonstrated that the KAT ActG could induce the acetylation of GtfB and GtfC enzymatically in S. mutans, providing insights into the function of lysine acetylation in bacterial virulence and pathogenicity.

Lysine acetylation is a regulatory post-translational modification (PTM) important in physiological processes across all domains of life. Although it has been well studied and characterized in eukaryotes, new insights into the lysine acetylation in bacteria have gained momentum in recent years, and hundreds to thousands of protein acetylation processes have been identified in various bacteria with novel enrichment strategies. However, the specific mechanisms of regulating lysine acetylation and function are still poorly understood. Therefore, we screened for the KAT mediating Gtfs acetylation by constructing 15 strains of S. mutans that overexpressed the GCN5-related N-acetyltransferases (GNAT) family members. Eventually, we identified and characterized ActG, a GNAT family member, that could catalyze the acetylation of GtfB and GtfC in S. mutans by the enzymatic mechanism, inversely related to their enzymatic activities, subsequently affecting the water-insoluble EPS synthesis and biofilm formation. In addition, ActG impaired the cariogenicity of S. mutans in a rat caries model. Thus, this study provides significant insights into the effect of lysine acetylation on S. mutans virulence and pathogenicity by regulating target protein functions and relative physiological processes.

Molecular mechanisms of inhibiting glucosyltransferases for biofilm formation in Streptococcus mutans

Glucosyltransferases (Gtfs) play critical roles in the etiology and pathogenesis of Streptococcus mutans (S. mutans)- mediated dental caries including early childhood caries. Gtfs enhance the biofilm formation and promotes colonization of cariogenic bacteria by generating biofilm extracellular polysaccharides (EPSs), the key virulence property in the cariogenic process. Therefore, Gtfs have become an appealing target for effective therapeutic interventions that inhibit cariogenic biofilms. Importantly, targeting Gtfs selectively impairs the S. mutans virulence without affecting S. mutans existence or the existence of other species in the oral cavity. Over the past decade, numerous Gtfs inhibitory molecules have been identified, mainly including natural and synthetic compounds and their derivatives, antibodies, and metal ions. These therapeutic agents exert their inhibitory role in inhibiting the expression gtf genes and the activities and secretion of Gtfs enzymes with a wide range of sensitivity and effectiveness. Understanding molecular mechanisms of inhibiting Gtfs will contribute to instructing drug combination strategies, which is more effective for inhibiting Gtfs than one drug or class of drugs. This review highlights our current understanding of Gtfs activities and their potential utility, and discusses challenges and opportunities for future exploration of Gtfs as a therapeutic target.

Draft Genome Sequence of Bacillus velezensis Strain Marseille-Q1230, Isolated from a Stool Sample from a Severely Malnourished Child

Bacillus velezensis, a species first described in 2005, has been mostly associated with plants and the environment. To date, there is no genome available for this species from human samples. In this announcement, we present the genome of Bacillus velezensis strain Marseille-Q1230, which was isolated from a stool sample from a child suffering from severe acute malnutrition. The genome assembled into 15 contigs and had a size of 3,861,152 bp, with a GC content of 46.6%. A total of 3,716 protein-coding genes, including 3 antibiotic resistance genes and 92 RNAs, were predicted.

Inhibitory effects of Lactobacillus brevis KU15153 against Streptococcus mutans KCTC 5316 causing dental caries

This study determined the inhibitory effect of Lactobacillus brevis KU15153 against cariogenic Streptococcus mutans KCTC 5316. Antimicrobial activity, auto-aggregation, cell surface hydrophobicity, exopolysaccharides (EPS) production, biofilm formation, and morphological changes were assessed in the presence of L. brevis KU15153. L. brevis KU15153 exhibited the highest antimicrobial activity against S. mutans KCTC 5316 (28.67 ± 4.16 mm). Auto-aggregation (38.32%), cell surface hydrophobicity (27.08%), and EPS production rate (58.52%) of S. mutans KCTC 5316 slightly decreased upon treatment with L. brevis KU15153. Additionally, crystal violet stanning and scanning electron microscopy confirmed the L. brevis KU15153-mediated inhibition of biofilm formation by S. mutans KCTC 5316 in comparison to that observed in the negative control (untreated S. mutans KCTC 5316). These results indicate that the L. brevis KU15153 could be used as a potential probiotic for maintaining oral health.

Effect of Rubusoside, a Natural Sucrose Substitute, on Streptococcus mutans Biofilm Cariogenic Potential and Virulence Gene Expression In Vitro

Dental caries is a biofilm-mediated disease in which Streptococcus mutans is the main pathogenic microorganism, and its incidence is closely related to sucrose. Rubusoside is a natural nonnutritive sweetener isolated from Rubus suavissimus S. Lee. This study was designed to determine the effect of this sucrose substitute on the cariogenic properties and virulence gene expression of S. mutans biofilms. S. mutans was exposed to brain heart infusion (BHI) medium (as a control), 1% sucrose-supplemented medium, 1% rubusoside-supplemented medium, and 1% xylitol-supplemented medium. The growth curve of the biofilm was monitored by crystal violet staining, and the pH was measured every 24 h. After 5 days, the biofilms formed on the glass coverslips were recovered to determine the biomass (dry weight and total amount of soluble proteins), numbers of CFU, and amounts of intra- and extracellular polysaccharides. Biofilm structural imaging was performed using a scanning electron microscope (SEM). Virulence gene expression (gtfB, gtfC, gtfD, ftf, spaP, gbpB, ldh, atpF, vicR, and comD) was determined by reverse transcription-quantitative PCR. Growth in rubusoside resulted in lower levels of acid production than observed during growth in sucrose, xylitol, and the control, while it also reduced the level of biofilm accumulation and bacterial viability and even reduced the level of production of extracellular polysaccharides. By SEM, the levels of biofilm formation and extracellular matrix during growth in rubusoside were lower than these levels during growth in sucrose and xylitol. From the perspective of virulence genes, growth in rubusoside and xylitol significantly inhibited the expression of virulence genes compared with their levels of expression after growth in sucrose. Among these genes, gtfB, gtfC, gbpB, ldh, and comD downregulation was found with growth in rubusoside compared with their expression with growth in xylitol. Therefore, rubusoside appears to be less potentially cariogenic than sucrose and xylitol and may become an effective sucrose substitute for caries prevention. Further studies are needed to deepen these findings.IMPORTANCE Dental caries is a major public health challenge and places heavy biological, social, and financial burdens on individuals and health care systems. To palliate the deleterious effect of sucrose on the virulence factors of S. mutans, massive commercial efforts have been oriented toward developing products that may act as sucrose substitutes. Rubusoside, a natural sucrose substitute, is a plant extract with a high level of sweetness. Although some studies have shown that rubusoside does not produce acids or inhibit the growth of S. mutans, little attention has been paid to its effect on dental biofilm and the underlying mechanisms. Our study focuses on the effect of rubusoside on the formation and structure of biofilms and the expression of virulence genes. The results confirm that rubusoside can inhibit accumulation, bacterial viability, polysaccharide production by the biofilm, and related gene expression. These results provide further insight into the cariogenicity of S. mutans biofilms and demonstrate a new perspective for studying the impact of sucrose substitutes on caries.

N-Nonyloxypentyl-l-Deoxynojirimycin Inhibits Growth, Biofilm Formation and Virulence Factors Expression of Staphylococcus aureus

Staphylococcus aureus is one of the major causes of hospital- and community-associated bacterial infections throughout the world, which are difficult to treat due to the rising number of drug-resistant strains. New molecules displaying potent activity against this bacterium are urgently needed. In this study, d- and l-deoxynojirimycin (DNJ) and a small library of their N-alkyl derivatives were screened against S. aureus ATCC 29213, with the aim to identify novel candidates with inhibitory potential. Among them, N-nonyloxypentyl-l-DNJ (l-NPDNJ) proved to be the most active compound against S. aureus ATCC 29213 and its clinical isolates, with the minimum inhibitory concentration (MIC) value of 128 μg/mL. l-NPDNJ also displayed an additive effect with gentamicin and oxacillin against the gentamicin- and methicillin-resistant S. aureus isolate 00717. Sub-MIC values of l-NPDNJ affected S. aureus biofilm development in a dose-dependent manner, inducing a strong reduction in biofilm biomass. Moreover, real-time reverse transcriptase PCR analysis revealed that l-NPDNJ effectively inhibited at sub-MIC values the transcription of the spa, hla, hlb and sea virulence genes, as well as the agrA and saeR response regulator genes.

Complete genome sequence and antimicrobial activity of Bacillus velezensis JT3-1, a microbial germicide isolated from yak feces

Bacillus velezensis JT3-1 was isolated from feces of the domestic yak (Bos grunniens) in Gansu province of China. Aim to know whether B. velezensis JT3-1 has the potency to be developed as a probiotic bacterium, works on the complete genome sequence, antimicrobial activity, growth performance in calves, and treatment effect on calf diarrhea of B. velezensis JT3-1 were carried out. The results showed that the complete genome of B. velezensis JT3-1 contains one gapless circular chromosome which is 3,929,799 bp, and has 3761 protein-encoding genes with an average GC content of 46.50%. From the antimicrobial activity results, B. velezensis JT3-1 has shown strong antagonistic activities against Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella Typhimurium, Mannheimia haemolytica, Staphylococcus hominis, Clostridium perfringens, and Mycoplasma bovis. Compared with the control group, the average weight of the experiment animals from Bv1 group and Bv2 group which were supplemented with B. velezensis JT3-1 was significantly increased (P < 0.05). Meanwhile, the Bv1 and Bv2 supplement significantly improved the level of IgA, IgG, IgM, and IFN-γ in calves as compared with the controls (P < 0.05), but the IL-2 level was not obviously changed between the three groups. In addition, B. velezensis JT3-1 showed a good effect against diarrhea, as the cure rate reached 95.0% (171/180) in newborn calves (Angus cattle) in Xinjiang, and 100.0% (149/149) in yak calves in Qinghai, respectively. Our study will lay a good foundation for the elucidation of the molecular mechanisms of its antimicrobial activity, and supports the hypothesis that JT3-1 has the potential to be developed as a probiotic bacterium in cattle.

Genome Sequence of Lipopeptide- and Antioxidant-Producing Strain Bacillus velezensis NWUMFkBS10.5

Candidate biocontrol agent Bacillus velezensis NWUMFkBS10.5 possesses unique genomic characteristics revealed by antiSMASH analysis and in vitro metabolomic elucidation. Besides its capability to produce antimicrobial lipopeptides, further in silico genome profiling predicted the presence of metabolic pathways for synthesizing antioxidants like lampranthin-2, miraxanthin V, and 2-decarboxybetanidin.