Extracellular Polysaccharide Production Research Articles

Effects of metal nanoparticles of iron, copper and cobalt on the growth of nitrogen-fixing bacterium Sinorhizobium fredii T14 and nodulation in soybean roots

Soybean is a high valuable crop of Vietnam and many other countries. The ability of soybean plants in nitrogen fixation and soil improvement is attributed to their symbiosis with different rhizobia in the root nodules. It has been well documented that members of genus Rhizobium are the most effective in nodulation and nitrogen fixation in legumes. Recently, in oder to minimize undesired accumulation of agro-chemicals and metal salts in soil, nanotechnology products have been intensively studied and applied as nanofertilizers. In this report, the effect of nanoparticles of iron, cobalt and copper on the in vitro growth of nitrogen fixing bacterium Sinorhizobium fredii T14 and nodulation in the root of soybean DT26 was studied. In the cultures of S. fredii T14, nano Fe at the final concentrations of 2, 5, 10, 25 and 50 ppm did not affect the growth, but the latter was reduced of 20, 35 and 46% at 100, 250 and 500 ppm, respectively. No growth inhibition was observed at nano Co concentrations below 10 ppm, while it was reduced of 73% at 500 ppm. Nano Cu seemed to have significant adverse effect on S. fredii T14, showing growth inhibition of 23, 68 and 100% at the concentrations of 5, 25 ppm and 50 ppm, respectively. The production of extracellular polysaccharide by S. fredii T14 was not affected at the concentrations of nano Fe and Co below 250 ppm, while drastic decrease occurred at the presence of nano Cu. Laboratory experiments showed that nanoparticles of all three studied metals at extremely low concentration of 2 ppm significantly increased the number of effective nodules in the roots of soybean DT26 and enhanced the plant growth.

Antibiofilm potential of lactobionic acid against Salmonella Typhimurium

This study aimed to explore the antibiofilm activity and possible mechanism of lactobionic acid (LBA) against Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium). The minimum inhibitory concentration (MIC) of LBA against S. Typhimurium was 8 mg/mL. At sub-inhibitory concentrations (SICs), LBA inhibited the biofilm formation of S. Typhimurium on glass surface, as evidenced by the results of microscope observations. Crystal violet staining assay and cell enumeration assay revealed that LBA was also effective in inhibiting the biofilm formation on stainless steel surface. Moreover, LBA repressed the swimming and swarming motility of S. Typhimurium and also reduced the production of extracellular polysaccharide and protein during biofilm formation. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis revealed that LBA down-regulated the expression of genes involved in S. Typhimurium biofilm formation. These data suggested that LBA exerted an inhibitory effect on S. Typhimurium biofilm formation through interfering with cell motility, extracellular polysaccharide and protein production as well as expression of biofilm-related genes. Additionally, LBA at 4MIC and 8MIC had the efficacy to inactivate S. Typhimurium biofilms formed on stainless steel and chicken meat.

A comprehensive review on yogurt syneresis: effect of processing conditions and added additives.

Yogurt, produced by the lactic fermentation of milk base, is an important dairy product worldwide. One of the essential sensory properties of yogurt is the texture, and some textural defects such as weak gel firmness and syneresis likely occur in various types of yogurts, affecting consumer acceptance. In this regard, various strategies such as enrichment of milk-based with different additives and ingredients such as protein-based components (skimmed milk powder (SMP), whey protein-based powders (WP), casein-based powders (CP), and suitable stabilizers, as well as modification of processing conditions (homogenization, fermentation, and cooling), can be applied in order to reduce syneresis. The most effective proteins and stabilizers in syneresis reduction are CP and gelatin, respectively. Furthermore, yogurt's water holding capacity and syneresis can be affected by the type of starter cultures, the protolithic activity, production of extracellular polysaccharides, and inoculation rate. Moreover, optimizing the heat treatment process (85°C/30min and 95°C/5min), homogenization (single or dual-stage), incubation temperature (around 40°C), and two-step cooling process can decrease yogurt syneresis. This review is aimed to investigate the effect of fortification of the milk base with various additives and optimization of process conditions on improving texture and preventing syneresis in yogurt.

Extracellular Polysaccharide Extraction from Streptococcus thermophilus in Fermented Milk.

ABSTRACTLactic acid bacteria such as Streptococcus thermophilus are known to produce extracellular polysaccharide (EPS) in fermented foods that enhance the creaminess and mouthfeel of the product, such as yogurt. Strains producing larger amounts of EPS are highly sought-after, and therefore, robust and accurate quantification methodologies are important. This study found that two commonly used methodologies significantly underestimated the amount of EPS produced as measured using a milk matrix. To this end, a proteolytic step was implemented prior to EPS extraction (Method C). An initial proteolytic step using xanthan gum-spiked milk significantly increased recovery yield to 64%, compared to 27.8% for Method A and 34.3% for Method B. Method C showed no improvement when assessed using a chemically defined medium. Method C was further validated using three strains of S. thermophilus with varying EPS-production capabilities (STLOW, STMID, STHIGH). Overall, Method C demonstrated significant improvements in the EPS extraction yield for all three S. thermophilus strains in fermented milk. On average, Method C improved isolation yield by ∼3- to 6-fold compared with Method A and by ∼2- to 3-fold compared with method B. There were no significant differences between samples when they were grown in a chemically defined medium, highlighting the importance of a proteolytic step specifically for fermented milk samples. In commercial applications, accurate quantification of EPS-production is an important aspect when finding new strains.IMPORTANCE Extracellular polysaccharide (EPS) production by milk-fermenting microorganisms is a highly sought-after trait in improving the perceived thickness, creaminess, and mouthfeel of yogurt. Streptococcus thermophilus are commonly isolated and their EPS production is quantified in the search for higher-producing strains. In this study, we demonstrated that two commonly used methods for isolating EPS from milk samples significantly underestimated the true amount of EPS present. We demonstrated that the addition of a proteolytic step prior to EPS extraction isolated over 2-fold more EPS than identical samples processed using the traditional protocols. We further validated this method in fermented milk samples from three strains of S. thermophilus that included a low-, mid-, and high-EPS producing strain. Again, we showed significant improvements in EPS isolation using a proteolytic step. In the search for new S. thermophilus strains with enhanced EPS production, accurate quantification in an optimal medium is essential.

Beneficial effects of magnetite nanoparticles on soybean-Bradyrhizobium japonicum and alfalfa-Sinorhizobium meliloti associations

Nanoparticles (NPs)-based growth stimulators have promising usage in agriculture. This research analyzed the impact of citric acid-coated magnetite nanoparticles (Fe3O4-NPs; 50 mg Fe L−1) added once at pre-sowing on soybean and alfalfa seedlings growing in association with their corresponding microsymbiont partners, Bradyrhizobium japonicum and Sinorhizobium meliloti; also on the in vitro growth rate of these microorganisms. Fe-EDTA (50 mg Fe L−1) was used as a comparator.Fe3O4-NPs significantly augmented the growth rate constant (7–17%) and extracellular polysaccharides production of both microsymbionts (B. japonicum: 2-fold; S. meliloti: 43%), which probably favored bacterial adhesion to the root hairs.In both legumes, Fe3O4-NPs increased chlorophyll content (up to 56% in soybean) and improved plant growth, evidenced by a greater root biomass system (80–90% higher than the control), and increased shoot biomass (30–40%). Besides, Fe3O4-NPs addition resulted in earlier nodule formation and enhanced nodule biomass (about 2.5-fold in both species). Nodules were mainly located in the crown of the root in the NP50 treatment, while they were evenly distributed along lateral roots in the control and the comparator. Fe3O4-NPs also augmented significantly nodule leghemoglobin content (∼50–70%) and total N in legumes’ shoots (ca. 20%). CAT activity increased only under NP50 treatment and no symptoms of oxidative damage were evidenced. In this work, we found that besides not being toxic neither to soybean and alfalfa plants nor to their microsymbiont partners, Fe3O4-NPs do not exert adverse effects on the symbioses establishment; oppositely, a more efficient nodulation pattern was verified in both plant species.

The Antimicrobial Effect of Melissa officinalis L. Essential Oil on Vibrio parahaemolyticus: Insights Based on the Cell Membrane and External Structure.

The study was to evaluate the antimicrobial impacts on Melissa officinalis L. essential oil (MOEO) against Vibrio parahaemolyticus. The minimum inhibitory concentration (MIC) of MOEO on Vibrio parahaemolyticus was 1 μL⋅mL–1. The kill-time curve exhibited that MOEO had good antimicrobial activity. The analysis of cellular ingredients leakage and cell viability illustrated that MOEO has destruction to the morphology of the cell membrane. The damage to the membrane integrity by MOEO has been confirmed by transmission and scanning electron microscopy, obvious morphological and ultrastructural changes were observed in the treated bacterial cells. The MOEO at 0.5 μL⋅mL–1 can inhibit the biofilm formation, biofilm motility, and extracellular polysaccharide production. Meanwhile, the qPCR results exhibited MOEO inhibited the expression of virulence genes. The findings showed that MOEO exerted its antimicrobial effect mainly by destroying the membrane, which indicated its potential as a natural food preservative.

Colonization by the Mycorrhizal Helper Bacillus pumilus HR10 Is Enhanced During the Establishment of Ectomycorrhizal Symbiosis Between Hymenochaete sp. Rl and Pinus thunbergii.

There are complex interactions between mycorrhizal helper bacteria (MHBs) and ectomycorrhizal (ECM) fungi, with MHBs promoting mycorrhizal synthesis and ECM fungi regulating plant rhizobacterial colonization, diversity, and function. In this study, to investigate whether the ECM fungus Hymenochaete sp. Rl affects the survival and colonization of the MHB strain Bacillus pumilus HR10 in the rhizosphere, the biomass of B. pumilus HR10 was measured in the rhizosphere and mycorrhizosphere. In addition, extracts of Hymenochaete sp. Rl and Pinus thunbergii were evaluated for their effect on B. pumilus HR10 colonization (growth, sporulation, biofilm formation, extracellular polysaccharide and extracellular protein contents, flagellar motility, and expression of colonization-related genes). The results showed that inoculation of Hymenochaete sp. Rl significantly increased the biomass of B. pumilus HR10 in the rhizosphere; however, while extracts of Hymenochaete sp. Rl and P. thunbergii did not affect the biomass or spore formation of HR10, they did affect its biofilm formation, extracellular polysaccharide and extracellular protein production, and flagellar motility. Furthermore, the addition of symbiont extracts affected the expression of chemotaxis-related genes in HR10. When the extracts were added separately, the expression of srf genes in HR10 increased; when the extracts were added simultaneously, the expression of the flagellin gene fliG in HR10 increased, but there was no significant effect on the expression of srf genes, consistent with the results on biofilm production. Thus, Hymenochaete sp. Rl and P. thunbergii roots had a positive effect on colonization by B. pumilus HR10 at the rhizosphere level through their secretions.

A rhizobial non-coding RNA has an effect on symbiotic nodulation by regulating an ABC transporter

Rhizobium leguminosarum has been widely used as a model to study nodule biochemistry, its genomic sequence has been published. We screened the Rhizobium leguminosarum bv. viciae 3841 genome sequence using a bioinformatics analysis for discovering potential small non-coding RNAs. One of these identified non-coding RNAs, cis-encoded antisense RLS1, was found to affect the symbiotic nodulation and nitrogen fixation. The mature form of RLS1 was 258 nt of non-coding RNA, its disruption mutant strain (△RLS1) caused that the nodulation stages were delayed dramatically and the total number of nodules decreased, leading to a 25% reduction in the total amount of nitrogen fixed in the symbiotic system of Rhizobium- Pisum sativum, compared with wild-type strain. RLS1 targets an ABC transporter mRNA, bind to Hfq in vitro, and to be stable in the absence of Hfq. Further analysis showed that Hfq is not required for interactions between RLS1 and its target mRNAs. △RLS1 strain exhibited that its production of extracellular polysaccharide (EPS) was over three times higher than in wild-type strain. The findings suggest that RLS1 might affect nodulation by participating in the regulatory network for EPS accurate secretion, playing a pivotal role in the infection process and in root nodule formation.

Design and synthesis novel amide derivatives containing an 1,3,4‐oxadiazole moiety as potential antibacterial agents

AbstractTo find new antibacterial agents, 25 novel amide derivatives containing an 1,3,4‐oxadiazole moiety were designed and synthesized, and their antibacterial activity against Xanthomonas oryzae pv. oryzicola (Xoc) and Xanthomonas oryzae pv. oryzae (Xoo) were tested. Interestingly, all target compounds showed excellent antibacterial activities against Xoc and Xoo. The EC50 values of compounds 1–25 against Xoc and Xoo were 1.2–4.0 mg/L and 0.5–2.3 mg/L, respectively, which were significantly superior to those of the thiodiazole copper (95.1 and 89.0 mg/L) and bismerthhibol (73.8 and 68.8 mg/L). For example, the EC50 values of compound 16 against Xoc and Xoo were 1.7 and 0.5 mg/L, respectively. Meanwhile, the curative and protection activity of compound 16 against rice bacterial leaf blight were 42.4% and 42.1%, respectively, which were superior to the control of jiahuangxianjunzuo (34.1% and 32.6%) and thiodiazole copper (33.0% and 27.1%). In addition, compound 16 might suppress the cell growth of Xoo by inhibiting the production of extracellular polysaccharide, the formation of biofilm, changes the cell membrane permeability, and cell surface morphology.

Plant growth-promoting and antibacterial activities of cultivable bacteria alive in tobacco field against Ralstonia solanacearum.

Bacterial wilt disease caused by Ralstonia solanacearum leads to decrease of crops yield. Investigation of cultivable bacteria diversity provides more microbial species for screening antagonistic bacteria. In the present study, a variety of cultivation methods were used to investigate the diversity of cultivable bacteria alive in tobacco field. A total of 441 bacterial strains were obtained that belonged to four phyla, 49 genera and 146 species. Actinobacteria and Proteobacteria were the dominant phyla. Agrobacterium, Arthrobacter, Bacillus, Klebsiella, Paenarthrobacter, Pseudomonas and Pseudarthrobacter were the dominant genera. Some rare genera were discovered including Bosea, Cedecea, Delftia and Dyella. Diversity, species and abundances of bacteria altered under different cultivation conditions. One hundred three bacterial strains showed plant growth-promoting attributes. Twenty Bacillus strains showed high antibacterial activity against R. solanacearum. In field experiments, individual strain and consortia of Bacillus subtilis, B. siamensis and B. vallismortis effectively inhibited bacterial wilt. The core genes that controlled synthesis of secondary metabolites were knocked out in B. vallismortis SSB-10. Difficidin, which was synthesized by dif operon and controlled by sfp gene, was the antibacterial substance produced by SSB-10. Difficidin destroyed cell wall and cell membrane of R. solanacearum and inhibited its motility, production of extracellular polysaccharides and cellulase activity.

Pseudomonas aeruginosa Oligoribonuclease Controls Tolerance to Polymyxin B by Regulating Pel Exopolysaccharide Production.

Polymyxins are considered as the last resort antibiotics to treat infections caused by multidrug-resistant Gram-negative pathogens. Pseudomonas aeruginosa is an opportunistic pathogen that causes various infections in humans. Proteins involved in lipopolysaccharide modification and maintaining inner and outer membrane integrities have been found to contribute to the bacterial resistance to polymyxins. Oligoribonuclease (Orn) is an exonuclease that regulates the homeostasis of intracellular (3'-5')-cyclic dimeric GMP (c-di-GMP), thereby regulating the production of extracellular polysaccharide in P. aeruginosa. Previously, we demonstrated that Orn affects the bacterial resistance to fluoroquinolone, β-lactam and aminoglycoside antibiotics. In this study, we found that mutation of orn increased the bacterial survival following polymyxin B treatment in a wild-type P. aeruginosa strain PA14. Overexpression of c-di-GMP degradation enzymes in the orn mutant reduced the bacterial survival. By using a fluorescence labeled polymyxin B, we found that mutation of orn increased the bacterial surface bound polymyxin B. Deletion of the Pel synthesis genes or treatment with a Pel hydrolase reduced the surface bound polymyxin B and bacterial survival. We further demonstrated that Pel binds to extracellular DNA (eDNA), which traps polymyxin B and thus protects the bacterial cells. Collectively, our results revealed a novel defense mechanism against polymyxin in P. aeruginosa.

Production, purification, and structural characteristics of extracellular polysaccharides derived from Lactobacillus acidophilus

BackgroundExtracellular polysaccharides (EPSs) derived from Lactobacillus acidophilus BCRC 10695 possess lots of beneficial effects to the host. In seeking to develop a fermentation process to produce EPSs, the culture medium compositions, purification, and structural analysis on EPSs were conducted. MethodsThe effects of carbon sources, nitrogen sources, and surfactants on EPSs production were explored. Response surface methodology (RSM) was applied for optimizing the cultivation medium. A four-step purification approach was carried out. The gas chromatography-mass spectrometry and NMR were applied for the EPSs structural analysis. FindingsThe optimal concentrations of sucrose, yeast extract and polysorbate 80 were 10.15 g/l, 25 g/l and 2 g/l respectively. The best EPS production was 923.7 mg/l in the late stationary phase of cultivation for 96 h, close to that in the experiment of 923.6 mg/l. The purification approach was able to remove 99.9% proteins and 98.5% of nucleic acid. Structural analysis showed EPSs consisted of mannose, ribose, glucose and galactose in ratios of 60.0: 22.8: 15.0: 2.2 and comprised (1→ 2) (1→6)-Mannose as backbone.

Extended biofilm formation time by Streptococcus sanguinis modifies its non-cariogenic behavior, in vitro.

Although the commensal Streptococcus sanguinis [ S. sanguinis] is isolated from caries-free people, it can ferment carbohydrates producing acids. We aimed to characterize S. sanguinis cariogenic potential as a function of different enamel biofilm formation periods, in vitro. Saliva-coated enamel slabs were inoculated with S. sanguinis to form initial biofilms for 8, 12 or 16 h in presence of sucrose and followed by a period in medium with glucose for 16, 12 or 8 h, respectively, until completion of 24 h. To simulate cariogenic challenges, S. sanguinis biofilms were exposed to 10% sucrose for 5 minutes, 3x/day for 5 days. Biofilm biomass, viable cells, total proteins, intracellular and extracellular polysaccharides production, acidogenicity and enamel demineralization were determined. Biofilms of Streptococcus mutans [ S. mutans ] served as caries-positive control. Biofilms of S. sanguinis forming on enamel for 12 and 16 h showed higher demineralization than those formed during 8 h, but lower than S. mutans biofilms, regardless of the initial biofilm formation time. No differences were detected in the biofilm properties among the different biofilm formation times tested for S. sanguinis . Increased enamel initial biofilm formation time by S. sanguinis appears to induce a cariogenic potential, but lower than S. mutans .

Immobilization of Lactic acid bacteria for production of extracellular polysaccharides

Lactic acid bacteria (LAB) can produce extracellular polysaccharides that can be used as thickeners, emulsifiers, and gels in foods. The immobilization technology can effectively simplify and improve the separation and regeneration of extracellular polysaccharides. In this study, six strains of LAB, including the extracellular polysaccharide-producing strain Lactobacillus plantarum, were screened. The different immobilized carriers of sodium alginate, agar, gelatin-glutaraldehyde, and carrageenan were assessed for fermentation by these six LAB. Different diameters of beads were selected, and the optimum culture temperature, carrier concentration, and inoculum volume were evaluated. The results showed that the agar-embedding method was the best immobilization method and the optimum process conditions were as follows: 3% inoculum of L. plantarum, 30 g/L of agar as immobilization carrier with a particle diameter of 1 cm, and fermentation at 37 °C for 24 h. Through orthogonal experiments, the maximum exopolysaccharide (EPS) yield obtained was 1489.9 mg/L.

MiR395-regulated sulfate metabolism exploits pathogen sensitivity to sulfate to boost immunity in rice

MicroRNAs (miRNAs) play important roles in plant physiological activities. However, their roles and molecular mechanisms in boosting plant immunity, especially through the modulation of macronutrient metabolism in response to pathogens, are largely unknown. Here, we report that an evolutionarily conserved miRNA, miR395, promotes resistance to Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), two destructive bacterial pathogens, by regulating sulfate accumulation and distribution in rice. Specifically, miR395 targets and suppresses the expression of the ATP sulfurylase gene OsAPS1, which functions in sulfate assimilation, and two sulfate transporter genes, OsSULTR2;1 and OsSULTR2;2, which function in sulfate translocation, to promote sulfate accumulation, resulting in broad-spectrum resistance to bacterial pathogens in miR395-overexpressing plants. Genetic analysis revealed that miR395-triggered resistance is involved in both pathogen-associated molecular pattern-triggered immunity and R gene-mediated resistance. Moreover, we found that accumulated sulfate but not S-metabolites inhibits proliferation of pathogenic bacteria, revealing a sulfate-mediated antibacterial defense mechanism that differs from sulfur-induced resistance. Furthermore, compared with other bacteria, Xoo and Xoc, which lack the sulfate transporter CysZ, are sensitive to high levels of extracellular sulfate. Accordingly, miR395-regulated sulfate accumulation impaired the virulence of Xoo and Xoc by decreasing extracellular polysaccharide production and biofilm formation. Taken together, these results suggest that rice miR395 modulates sulfate metabolism to exploit pathogen sensitivity to sulfate and thereby promotes broad-spectrum resistance.

Transcription factor GlbHLH regulates hyphal growth, stress resistance, and polysaccharide biosynthesis in Ganoderma lucidum.

Basic helix-loop-helix (bHLH) transcription factors (TFs) participate in many physiological and cellular processes in eukaryotes. However, their functions remain unclear in the macro basidiomycete Ganoderma lucidum (G. lucidum). In this study, a gene encoding bHLH TF, GlbHLH, was identified in G. lucidum. The knockdown of GlbHLH by RNA interference reduced hyphal growth, hyphal branching, and resistant to osmotic, oxidative, and cell wall stress. The content of cell wall components β-1,3 glucan and chitin and the expression of their synthesis genes were decreased in the GlbHLH knockdown strains. The knockdown of GlbHLH led to an increase of intracellular reactive oxygen species by decreasing the enzyme activity and gene expression of antioxidant enzymes. Furthermore, the production of intracellular polysaccharides and extracellular polysaccharides was greatly decreased in the GlbHLH mutants. These results suggested that GlbHLH is involved in hyphal growth, stress response, and polysaccharide biosynthesis in G. lucidum.

Paeoniflorin reduce luxS/AI-2 system-controlled biofilm formation and virulence in Streptococcus suis

ABSTRACT Streptococcus suis (S. suis), more specifically serotype 2, is a bacterial pathogen that threatens the lives of pigs and humans. Like many other pathogens, S. suis exhibits quorum sensing (QS) system-controlled virulence factors, such as biofilm formation that complicates treatment. Therefore, impairing the QS involving LuxS/AI-2 cycle in S. suis, may be a promising alternative strategy for overcoming S. suis infections. In this study, we investigated paeoniflorin (PF), a monoterpenoid glycoside compound extracted from peony, as an inhibitor of S. suis LuxS/AI-2 system. At a sub-minimal inhibitory concentration (MIC) (1/16 MIC; 25 μg/ml), PF significantly reduced biofilm formation by S. suis through inhibition of extracellular polysaccharide (EPS) production, without affecting bacterial growth. Moreover, evidence was brought that PF reduces AI-2 activity in S. suis biofilm. Molecular docking indicated that LuxS may be the target of PF. Monitoring LuxS enzymatic activity confirmed that PF had a partial inhibitory effect. Finally, we showed that the use of PF in a mouse model can relieve S. suis infections. This study highlighted the anti-biofilm potential of PF against S. suis, and brought evidence that it may as an inhibitor of the LuxS/AI-2 system to prevent S. suis biofilm-related infections. PF can thus be used as a new type of natural biofilm inhibitor for clinical application.

PsrA is a novel regulator contributes to antibiotic synthesis, bacterial virulence, cell motility and extracellular polysaccharides production in Serratia marcescens.

Serratia marcescens is a Gram-negative bacterium of the Enterobacteriaceae family that can produce numbers of biologically active secondary metabolites. However, our understanding of the regulatory mechanisms behind secondary metabolites biosynthesis in S. marcescens remains limited. In this study, we identified an uncharacterized LysR family transcriptional regulator, encoding gene BVG90_12635, here we named psrA, that positively controlled prodigiosin synthesis in S. marcescens. This phenotype corresponded to PsrA positive control of transcriptional of the prodigiosin-associated pig operon by directly binding to a regulatory binding site (RBS) and an activating binding site (ABS) in the promoter region of the pig operon. We demonstrated that L-proline is an effector for the PsrA, which enhances the binding affinity of PsrA to its target promoters. Using transcriptomics and further experiments, we show that PsrA indirectly regulates pleiotropic phenotypes, including serrawettin W1 biosynthesis, extracellular polysaccharide production, biofilm formation, swarming motility and T6SS-mediated antibacterial activity in S. marcescens. Collectively, this study proposes that PsrA is a novel regulator that contributes to antibiotic synthesis, bacterial virulence, cell motility and extracellular polysaccharides production in S. marcescens and provides important clues for future studies exploring the function of the PsrA and PsrA-like proteins which are widely present in many other bacteria.

The vicK gene of Streptococcus mutans mediates its cariogenicity via exopolysaccharides metabolism

Streptococcus mutans (S. mutans) is generally regarded as a major contributor to dental caries because of its ability to synthesize extracellular polysaccharides (EPS) that aid in the formation of plaque biofilm. The VicRKX system of S. mutans plays an important role in biofilm formation. The aim of this study was to investigate the effects of vicK gene on specific characteristics of EPS in S. mutans biofilm. We constructed single-species biofilms formed by different mutants of vicK gene. Production and distribution of EPS were detected through atomic force microscopy, scanning electron microscopy and confocal laser scanning microscopy. Microcosmic structures of EPS were analyzed by gel permeation chromatography and gas chromatography-mass spectrometry. Cariogenicity of the vicK mutant was assessed in a specific pathogen-free rat model. Transcriptional levels of cariogenicity-associated genes were confirmed by quantitative real-time polymerase chain reaction. The results showed that deletion of vicK gene suppressed biofilm formation as well as EPS production, and EPS were synthesized mostly around the cells. Molecular weight and monosaccharide components underwent evident alterations. Biofilms formed in vivo were sparse and contributed a decreased degree of caries. Moreover, expressional levels of genes related to EPS synthesis were down-regulated, except for gtfB. Our report demonstrates that vicK gene enhances biofilm formation and subsequent caries development. And this may due to its regulations on EPS metabolism, like synthesis or microcosmic features of EPS. This study suggests that vicK gene and EPS can be considered as promising targets to modulate dental caries.

Molecular mechanism of increasing extracellular polysaccharide production of Paenibacillus mucilaginosus K02 by adding mineral powders

Bacterial polysaccharides are widely applied in a range of products and increasing bacterial polysaccharide production is important commercially. In this study, attapulgite, serpentine, talc, biotite, and hydroxylapatite were used to stimulate extracellular polysaccharide (EPS) production by Paenibacillus mucilaginosus K02. The viscosity, polysaccharides, and proteins in culture medium in shaking flasks were quantified after addition of different minerals to the culture medium, and the molecular mechanism of serpentine on stimulating bacterial EPS synthesis was further revealed by proteomic and metabolomic analysis. The results showed that the viscosity, EPS, and protein contents in the culture were significantly increased by the introduction of minerals. The underlying mechanism for increased EPS production was due to a series of protective strategies of the bacterium against the damage arising from collision and friction caused by mineral powders. That is, bacteria protect and maintain their normal life by synthesis and secretion of excessive EPS, enhancement of oxidation resistance and secretion of various organic acids under these mineral treatments. The results not only show the importance of polysaccharide production for bacteria survival under adverse conditions, but also provide a new way of increasing bacterial production of more EPSs.