Extracellular Polysaccharide Production Research Articles

Effect of Different Concentrations of NaCl on Growth and Biochemical Characteristics of Red Microalga Porphyridium cruentum

The red microalga Porphyridium cruentum is a potential source of valuable biologically active compounds. This microalga is easily cultivated and could change its growth and biochemical composition in response to environmental variations. The effect of growth medium content, especially salinity (15, 20, and 27 gL -1 NaCl) on P. cruentum cell growth, biomass composition, and extracellular polysaccharides production was investigated in this study. The results showed that the highest biomass yield and phycoerythrin content was achieved when NaCl in a concentration of 20 gL -1 was introduced into the culture medium. The measured biomass was equal to 4.3±0.1 gL -1 compared to 3.3±0.1 gL -1 for the control sample at the end of the cultivation process. The amount of chlorophyll „a“ was also 1.33 times greater in the sample with 20 gL -1 NaCl compared to the control sample with 27 gL -1 , where the carotenoid content was higher. The highest amount of extracellular polysaccharide was accumulated by the microalga at 27 gL -1 NaCl. The measured viscosity was 3.35 mPa.sec - 1.4 times more than the sample with 20 gL -1 NaCl. The investigations conveyed lead to the conclusion that with only slight changes in the salt concentration, a targeted biosynthesis could be achieved, nevertheless, all other conditions remained the same. The study provides an opportunity to optimize growth and metabolite production using optimization in the cultivation process of the microalgae.

Antibacterial mechanism of areca nut essential oils against Streptococcus mutans by targeting the biofilm and the cell membrane.

Dental caries is one of the most common and costly biofilm-dependent oral diseases in the world. Streptococcus mutans is the major cariogenic pathogen of dental caries. S. mutans synthesizes extracellular polysaccharides by autologous glucosyltransferases, which then promotes bacterial adhesion and cariogenic biofilm formation. The S. mutans biofilm is the principal target for caries treatment. This study was designed to explore the antibacterial activity and mechanisms of areca nut essential oil (ANEO) against S. mutans. The ANEOs were separated by negative pressure hydro-distillation. The Kirby-Bauer method and broth microdilution method were carried out to evaluate the antibacterial activity of different ANEOs. The antibacterial mechanism was revealed by crystal violet staining, XTT reduction, microbial adhesion to hydrocarbon test, extracellular polysaccharide production assay, glucosyltransferase activity assay, lactate dehydrogenase leaking, propidium iodide staining and scanning electron microscopy (SEM). The cytotoxicity of ANEOs was determine by MTT assay. The ANEOs separated at different temperatures exhibited different levels of antibacterial activity against S. mutans, and the ANEO separated at 70°C showed the most prominent bacteriostatic activity. Anti-biofilm experiments showed that the ANEOs attenuated the adhesion ability of S. mutans by decreasing the surface hydrophobicity of the bacteria, prevented S. mutans biofilm formation by inhibiting glucosyltransferase activity, reducing extracellular polysaccharide synthesis, and reducing the total biofilm biomass and activity. SEM further demonstrated the destructive effects of the ANEOs on the S. mutans biofilm. Cell membrane-related experiments indicated that the ANEOs destroyed the integrity of the cell membrane, resulting in the leakage of lactic dehydrogenase and nucleic acids. SEM imaging of S. mutans cell showed the disruption of the cellular morphology by the ANEOs. The cytotoxicity assay suggested that ANEO was non-toxic towards normal oral epithelial cells. This study displayed that ANEOs exerted antibacterial activity against S. mutans primarily by affecting the biofilm and disrupting the integrity of the cell membrane. ANEOs has the potential to be developed as an antibacterial agent for preventing dental caries. Additionally, a new method for the separation of essential oil components is presented.

Effects of Sulforaphene on the Cariogenic Properties of Streptococcus Mutans In Vitro and Dental Caries Development In Vivo.

Sulforaphene (SFE) is a common nutritional supplement with antibacterial, anti-cancer, and anti-inflammatory effects. However, the effects of SFE on the cariogenicity of Streptococcus mutans and dental caries have not been reported. The objectives of this study were to investigate the caries-controlling potential of SFE. The effects of SFE on S. mutans were investigated using the broth microdilution method, crystal violet staining, SEM observation, acid tolerance assays, lactic acid quantification, and polysaccharide measurements. A rat caries model was established to evaluate the caries-controlling effects and biocompatibility of SFE in vivo. SFE inhibited S. mutans growth and biofilm formation. Furthermore, SFE restrained the cariogenic properties of S. mutans, including its acid production, acid tolerance, and extracellular polysaccharide production, without affecting the bacterial viability at sub-inhibitory levels. In the rat caries model, SFE significantly arrested the onset and development of dental caries. Moreover, no visible hemolytic phenomenon or cytotoxicity was detected in the SFE groups. After four weeks of SFE treatment, all rats remained in apparent good health with no significant differences in weight gain; their hemogram and biochemical parameters were normal; no pathological changes were observed in the oral mucosa, liver, or kidneys. In conclusion, SFE was safe and inhibited the development of caries effectively.

Antibacterial Effects of Ramulus mori Oligosaccharides against Streptococcus mutans.

Ramulus mori has been widely used in traditional Chinese medicine because of its physiological activities, including antibacterial, anti-inflammatory, and antioxidant activities. Antimicrobial properties of Ramulus mori extract have been well described. However, no information is available regarding on Ramulus mori oligosaccharides (RMOS). The aim of this study was to investigate the effects of RMOS on the growth and virulence properties of the cariogenic bacterium Streptococcus mutans. The effects of RMOS on the biofilm structure and virulence gene expression of S. mutans were also evaluated, and the results were compared with the effects of commercial prebiotic galactooligosaccharides. RMOS were found to have an antibacterial effect against S. mutans, resulting in significant reductions in acid production, lactate dehydrogenase activity, adhesion, insoluble extracellular polysaccharide production, glucosyltransferase activity, and biofilm formation in a dose-dependent manner. Moreover, the biofilm structure was visibly damaged. A quantitative real-time PCR assay revealed downregulation of virulence gene-regulated acid production, polysaccharide production, adhesion, biofilm formation, and quorum sensing. These findings suggest that RMOS may be a promising natural product for the prevention of dental caries.

Indole-3-acetic acid mediated removal of sludge toxicity by microalgae: Focus on the role of extracellular polymeric substances

The use of indole-3-acid (IAA) as an additive aided in achieving the objectives of reducing sludge extract toxicity, increasing Tetradesmus obliquus biomass yield, and enhancing extracellular polysaccharide production. Proteomics analysis can unveil the microalgae’s response mechanism to sludge toxicity stress. With 10-6 M IAA addition, microalgae biomass reached 3.426 ± 0.067 g/L. Sludge extract demonstrated 78.3 ± 3.2% total organic carbon removal and 72.2 ± 2.1% toxicity removal. Extracellular polysaccharides and proteins witnessed 2.08 and 1.76-fold increments, respectively. Proteomic analysis indicated that Tetradesmus obliquus directed carbon sources towards glycogen accumulation and amino acid synthesis, regulating pathways associated with carbon metabolism (glycolysis, TCA cycle, and amino acid metabolism) to adapt to the stressful environment. These findings lay the groundwork for future waste sludge treatment and offer novel insights into microalgae cultivation and extracellular polysaccharide enrichment in sludge.

The role of extracellular polysaccharide produced by Bradyrhizobium strain in root growth, improvement of soil aggregate stability and reduction of soil detachment capacity

It is well demonstrated that the production of extracellular polysaccharide by bacteria, as biological binding agent, can increase soil aggregate stability. Also, plant roots have significant effects on the soil erosion rates, since they can strongly change the soil detachment capacity (Dc). This study quantifies Dc at different flow rates in soils treated with biofertilizer under four species (Alnus subcordata, Brachythecium plumose, Gleditsia caspica and Sambucus ebulus species) in the Saravan forest park of Iran and develops regression equations for predicting Dc. Undisturbed samples collected from soils with the four tree species and subjected to five slopes (from 4.2 to 38.3%) and five water discharges (from 0.28 to 0.71 L m−1 s−1) using a hydraulic flume. The results showed that Dc was significantly lower in soils with Alnus subcordata species compared to Brachythecium plumose, Gleditsia caspica and Sambucus ebulus species, as the consequence of the changes in the root characteristics, mean weight diameter (MWD) and macronutrients, so that Dc was negatively correlated with root weight density, root length and root biomass. A linear regression model was found for MWD as a function of extracellular polysaccharide concentration (R2 = 0.74). The unit stream power had high accuracy for predicting Dc for all of the studied species. The lowest value of rill erodibility (Kr) was obtained in soils with Alnus subcordata species using regression relationship between the Dc and the shear stress of the soil. This experiment helped to show the importance of microorganisms in reducing the soil detachment rates and provided a contribution in understanding the choice of appropriate species for soil conservation.

Modeled energetics of bacterial communities in ancient subzero brines.

Cryopeg brines are isolated volumes of hypersaline water in subzero permafrost. The cryopeg system at Utqiaġvik, Alaska, is estimated to date back to 40 ka BP or earlier, a remnant of a late Pleistocene Ocean. Surprisingly, the cryopeg brines contain high concentrations of organic carbon, including extracellular polysaccharides, and high densities of bacteria. How can these physiologically extreme, old, and geologically isolated systems support such an ecosystem? This study addresses this question by examining the energetics of the Utqiaġvik cryopeg brine ecosystem. Using literature-derived assumptions and new measurements on archived borehole materials, we first estimated the quantity of organic carbon when the system formed. We then considered two bacterial growth trajectories to calculate the lower and upper bounds of the cell-specific metabolic rate of these communities. These bounds represent the first community estimates of metabolic rate in a subzero hypersaline environment. To assess the plausibility of the different growth trajectories, we developed a model of the organic carbon cycle and applied it to three borehole scenarios. We also used dissolved inorganic carbon and nitrogen measurements to independently estimate the metabolic rate. The model reconstructs the growth trajectory of the microbial community and predicts the present-day cell density and organic carbon content. Model input included measured rates of the in-situ enzymatic conversion of particulate to dissolved organic carbon under subzero brine conditions. A sensitivity analysis of model parameters was performed, revealing an interplay between growth rate, cell-specific metabolic rate, and extracellular enzyme activity. This approach allowed us to identify plausible growth trajectories consistent with the observed bacterial densities in the cryopeg brines. We found that the cell-specific metabolic rate in this system is relatively high compared to marine sediments. We attribute this finding to the need to invest energy in the production of extracellular enzymes, for generating bioavailable carbon from particulate organic carbon, and the production of extracellular polysaccharides for cryoprotection and osmoprotection. These results may be relevant to other isolated systems in the polar regions of Earth and to possible ice-bound brines on worlds such as Europa, Enceladus, and Mars.

The potential use of glycosyl-transferase inhibitors for targeted reduction of S. mutans biofilms in dental materials

Streptococcus mutans is the primary oral caries-forming bacteria, adept at producing “sticky” biofilms via the synthesis of insoluble extracellular polysaccharides (EPS), catalyzed by glucosyltransferases (GTFs). To circumvent the use of broad-spectrum antibiotics to combat these bacteria, this study sought to modify existing EPS-targeting small molecules with the ultimate goal of producing anti-biofilm polymer surfaces specifically targeting S. mutans. To achieve this, a known GTF inhibitor (G43) was modified with methoxy or tetraethyleneglycol substitutions in different positions (nine derivatives, tested at 50-µM) to pinpoint potential sites for future methacrylate functionalization, and then assessed against single-species S. mutans biofilms. As expected, the compounds did not diminish the bacterial viability. In general, the compounds with methoxy substitution were not effective in reducing EPS formation, whereas the tetraethyleneglycol substitution (G43-C3-TEG) led to a decrease in the concentration of insoluble EPS, although the effect is less pronounced than for the parent G43. This aligns with the reduced GTF-C activity observed at different concentrations of G43-C3-TEG, as well as the consequent decrease in EPS formation, and notable structural changes. In summary, this study determined that G43-C3-TEG is non-bactericidal and can selectively reduce the biofilm formation, by decreasing the production of EPS. This molecule will serve to functionalize surfaces of materials to be tested in future research.

The Transcription Regulator GntR/HutC Regulates Biofilm Formation, Motility and Stress Tolerance in Lysobacter capsici X2-3.

Lysobacter capsici X2-3, a plant growth-promoting rhizobacteria (PGPR), was isolated from wheat rhizosphere and has inhibitory effects against a wide range of pathogens. One important characteristic of L. capsici is its ability to produce diverse antibiotics and lytic enzymes. The GntR family of transcription factors is a common transcription factor superfamily in bacteria that has fundamental roles in bacterial metabolism regulation. However, the GntR family transcription factor in Lysobacter has not been identified. In this study, to obtain an understanding of the GntR/HutC gene function in L. capsici X2-3, a random Tn5-insertion mutant library of X2-3 was constructed to select genes showing pleiotropic effects on phenotype. We identified a Tn5 mutant with an insertion in LC4356 that showed reduced biofilm levels, and sequence analysis indicated that the inserted gene encodes a GntR/HutC family transcription regulator. Furthermore, the LC4356 mutant showed reduced extracellular polysaccharide (EPS) production, diminished twitching motility and decreased survival under UV radiation and high-temperature. The RT‒qPCR results indicated that the pentose phosphate pathway-related genes G6PDH, 6PGL and PGDH were upregulated in the LC4356 mutant. Thus, since L. capsici is an efficient biocontrol agent for crop protection, our findings provide fundamental insights into GntR/HutC and will be worthwhile to improve PGPR biocontrol efficacy.

Antibiofilm Activity and Mechanism of Linalool against Food Spoilage Bacillus amyloliquefaciens.

Pellicle biofilm-forming bacteria Bacillus amyloliquefaciens are the major spoilage microorganisms of soy products. Due to their inherent resistance to antibiotics and disinfectants, pellicle biofilms formed are difficult to eliminate and represent a threat to food safety. Here, we assessed linalool's ability to prevent the pellicle of two spoilage B. amyloliquefaciens strains. The minimum biofilm inhibitory concentration (MBIC) of linalool against B. amyloliquefaciens DY1a and DY1b was 4 μL/mL and 8 μL/mL, respectively. The MBIC of linalool had a considerable eradication rate of 77.15% and 83.21% on the biofilm of the two strains, respectively. Scanning electron microscopy observations revealed that less wrinkly and thinner pellicle biofilms formed on a medium supplemented with 1/2 MBIC and 1/4 MBIC linalool. Also, linalool inhibited cell motility and the production of extracellular polysaccharides and proteins of the biofilm matrix. Furthermore, linalool exposure reduced the cell surface hydrophobicity, zeta potential, and cell auto-aggregation of B. amyloliquefaciens. Molecular docking analysis demonstrated that linalool interacted strongly with quorum-sensing ComP receptor and biofilm matrix assembly TasA through intermolecular hydrogen bonds, hydrophobic contacts, and van der Waals forces interacting with site residues. Overall, our findings suggest that linalool may be employed as a potential antibiofilm agent to control food spoilage B. amyloliquefaciens.

Increased production of extracellular polysaccharides in Arthrospira platensis as a protective response against saxitoxin: Implications to outdoor mass production

Cyanobacteria of both toxic and nontoxic species frequently coexist and thrive in the same habitat. However, little is known about how nontoxic species can mitigate the negative impacts of the toxins produced by toxic species. The current study examined the potential adaptive response of Arthrospira platensis to saxitoxin (STX) in batch cultures. This cyanobacterium was exposed to various STX concentrations for seven days, and growth and antioxidative biomarkers were observed. During the first two days of incubation, the growth (i.e., cell density and chlorophyll-a) dramatically decreased in STX-treated cultures compared to control. Glutathione-S-transferase (GST), superoxide dismutase (SOD), and lipid peroxidation levels increased along with this decline in growth in STX-treated cultures. These parameters were restored to control values on day 3 of incubation and remained at levels that were relatively close to those of control cultures during the remaining period of experiment. The changes in these parameters were associated with the amount of extracellular polysaccharides (EPS) released into the media of STX-treated cultures, demonstrating the role of this EPS in protecting A. platensis cells from this toxin. The results of isotherm experiments confirmed the ability of the released EPS to adsorb STX onto their surfaces, with adsorption capacity (k = 2.9) comparable with that of activated carbon (k = 3.6). This suggests that A. platensis used EPS to build a defense mechanism to limit STX uptake into its cells. This EPS can give A. platensis the advantage of growing in natural lake water in outdoor systems for mass production without experiencing any negative effects from STX. Additionally, EPS could be used in drinking water and wastewater treatment facilities as an ecofriendly adsorbent for saxitoxin and other positively charged cyanotoxins.

EVALUATION OF ANTI-QUORUM SENSING ACTIVITY OF-HEXADECANOIC ACID PRODUCED BY PSEUDOMONAS STUTZERI SJ4 – A MARINE EPIBIOTIC BACTERIUM

Quorum sensing (QS) mechanism is cell communication that plays vital role in the development of infection by many pathogenic microorganisms. It controls multiple virulence factors such as pigmentation, biofilm formation, swarming motility, resistance towards antibiotics, extracellular polysaccharide production (EPS) and expression of several collective traits. The disruption of quorum sensing mechanism can be a solution to the emerging problem of multi-drug resistance among pathogenic bacteria. The effector molecule for Quorum sensing inhibition may be enzymatic or non- enzymatic in nature termed as Quorum Quenching (QQ) or Quorum sensing inhibitory (QSIs)/anti –QS compound, respectively. We used marine epibiotic bacteria as a source to obtained novel bacterial strain as QSI producer. One of the potent isolate, SJ4 was identified as Pseudomonas stutzeri SJ4, it is a short rod, gram negative bacterium. The ethyl acetate extract from P. stutzeri SJ4, showed highest QSI activity against monitor strain Chromobacterium violaceum (MTCC 5526). The extracted compound was tested against P. aeruginosa PAO1 at minimum inhibitiory concentration (MIC) and sub-MIC to study the effect on virulence factors. The significant inhibition of pycocyanin pigment, EPS production, rhamnolipid production and reduced swimming and swarming motility was observed. In addition, biofilm formation was notably inhibited which was confirmed by staining and spectometric method. Based on this observation, QS interption by extract which contain QSI remarkebly reduced the virulence of pathogen hence, can be use as therapeutic agents. The Thin Layer Chomatography (TLC) and Gas chrmoatography-Mass Spectrometry (GC-MS) identified major compound as n-Hexadecanoic acid. However, further research is required on purification of compound and its potential applications for the treatement of infections.

Effects of caffeic acid phenethyl ester against multi-species cariogenic biofilms.

Dental caries is a biofilm-related disease, widely perceived to be caused by oral ecological imbalance when cariogenic/aciduric bacteria obtain an ecological advantage. Compared with planktonic bacteria, dental plaques are difficult to remove under extracellular polymeric substance protection. In this study, the effect of caffeic acid phenethyl ester (CAPE) on a preformed cariogenic multi-species biofilm was evaluated, which was comprised of cariogenic bacteria (Streptococcus mutans), commensal bacteria (Streptococcus gordonii), and a pioneer colonizer (Actinomyces naeslundii). Our result revealed that treatment with 0.08mg/mL CAPE reduced live S. mutans in the preformed multi-species biofilm while not significantly changing the quantification of live S. gordonii. CAPE significantly reduced the production of lactic acid, extracellular polysaccharide, and extracellular DNA and made the biofilm looser. Moreover, CAPE could promote the H2O2 production of S. gordonii and inhibit the expression of SMU.150 encoding mutacin to modulate the interaction among species in biofilms. Overall, our results suggested that CAPE could inhibit the cariogenic properties and change the microbial composition of the multi-species biofilms, indicating its application potential in dental caries prevention and management.

Screening of medicinal mushroom strains with antimicrobial activity and polysaccharides production

AbstractObjectivesThis study aimed to determine the antimicrobial activity of culture fluid and mycelial mass of selectedHericiumstrains from the IBK Mushroom Culture Collection (Kyiv, Ukraine) against bacteria and fungi, as well as to evaluate the potential of these mushrooms for biomass and extracellular polysaccharides production.MethodsThe antimicrobial activity of ethyl acetate extracts of culture fluid and aqueous-ethyl extracts of mycelial mass for threeHericiumspecies:Hericium cirrhatumIBK 2393,Hericium coralloidesIBK 2332, andHericium erinaceusIBK 2530 against Gram-positiveBacillus subtilis,Staphylococcus aureus, and Gram-negativeEscherichia coli,Klebsiella pneumoniae,Pseudomonas aureginosabacteria as well asAspergillus niger,Penicillium polonicum, andMucor globosusfungi by the disk diffusion method was conducted. Analysis of the minimum inhibitory concentration was carried out according to the broth dilution method.ResultsHigh antimicrobial activity of culture fluid extracts ofHericiummushroom species againstS. aureuswas established after 14–21 days of cultivation. No effects ofHericiumextracts againstA. niger,P. polonicum, andM. globosuswere observed. On the 7th day of submerged cultivation, the studied strains produced the maximum yield of extracellular polysaccharides. The most promising extracellular polysaccharide (EPS) producers were strains ofH. coralloidesIBK 2332 (1.89 g/L) andH. erinaceusIBK 2530 (1.90 g/L). The maximal value of biomass was produced byH. cirrhatumIBK 2393 on the 21st day of submerged cultivation (17.45 g/L).ConclusionsHericiummushrooms have significant potential for the development of new drugs with health benefits properties.

Isolation, Characterization and Antibacterial Activity of 4-Allylbenzene-1,2-diol from Piper austrosinense.

Isolation for antibacterial compounds from natural plants is a promising approach to develop new pesticides. In this study, two compounds were obtained from the Chinese endemic plant Piper austrosinense using bioassay-guided fractionation. Based on analyses of 1H-NMR, 13C-NMR, and mass spectral data, the isolated compounds were identified as 4-allylbenzene-1,2-diol and (S)-4-allyl-5-(1-(3,4-dihydroxyphenyl)allyl)benzene-1,2-diol. 4-Allylbenzene-1,2-diol was shown to have strong antibacterial activity against four plant pathogens, including Xanthomonas oryzae pathovar oryzae (Xoo), X. axonopodis pv. citri (Xac), X. oryzae pv. oryzicola (Xoc) and X. campestris pv. mangiferaeindicae (Xcm). Further bioassay results exhibited that 4-allylbenzene-1,2-diol had a broad antibacterial spectrum, including Xoo, Xac, Xoc, Xcm, X. fragariae (Xf), X. campestris pv. campestris (Xcc), Pectobacterium carotovorum subspecies brasiliense (Pcb) and P. carotovorum subsp. carotovorum (Pcc), with minimum inhibitory concentration (MIC) values ranging from 333.75 to 1335 μmol/L. The pot experiment showed that 4-allylbenzene-1,2-diol exerted an excellent protective effect against Xoo, with a controlled efficacy reaching 72.73% at 4 MIC, which was superior to the positive control kasugamycin (53.03%) at 4 MIC. Further results demonstrated that the 4-allylbenzene-1,2-diol damaged the integrity of the cell membrane and increased cell membrane permeability. In addition, 4-allylbenzene-1,2-diol also prevented the pathogenicity-related biofilm formation in Xoo, thus limiting the movement of Xoo and reducing the production of extracellular polysaccharides (EPS) in Xoo. These findings suggest the value of 4-allylbenzene-1,2-diol and P. austrosinense could be as promising resources for developing novel antibacterial agents.

A 4-Hydroxybenzoic Acid-Mediated Signaling System Controls the Physiology and Virulence of Shigella sonnei.

Many bacteria use small molecules, such as quorum sensing (QS) signals, to perform intraspecies signaling and interspecies or interkingdom communication. Previous studies demonstrated that some bacteria regulate their physiology and pathogenicity by employing 4-hydroxybenzoic acid (4-HBA). Here, we report that 4-HBA controls biological functions, virulence, and anthranilic acid production in Shigella sonnei. The biosynthesis of 4-HBA is performed by UbiC (SSON_4219), which is a chorismate pyruvate-lyase that catalyzes the conversion of chorismate to 4-HBA. Deletion of ubiC caused S. sonnei to exhibit impaired phenotypes, including impaired biofilm formation, extracellular polysaccharide (EPS) production, and virulence. In addition, we found that 4-HBA controls the physiology and virulence of S. sonnei through the response regulator AaeR (SSON_3385), which contains a helix-turn-helix (HTH) domain and a LysR substrate-binding (LysR_substrate) domain. The same biological functions are controlled by AaeR and the 4-HBA signal, and 4-HBA-deficient mutant phenotypes were rescued by in trans expression of AaeR. We found that 4-HBA binds to AaeR and then enhances the binding of AaeR to the promoter DNA regions in target genes. Moreover, we revealed that 4-HBA from S. sonnei reduces the competitive fitness of Candida albicans by interfering with morphological transition. Together, our results suggested that the 4-HBA signaling system plays crucial roles in bacterial physiology and interkingdom communication. IMPORTANCE Shigella sonnei is an important pathogen in human intestines. Following previous findings that some bacteria employ 4-HBA as a QS signal to regulate biological functions, we demonstrate that 4-HBA controls the physiology and virulence of S. sonnei. This study is significant because it identifies both the signal synthase UbiC and receptor AaeR and unveils the signaling pathway of 4-HBA in S. sonnei. In addition, this study also supports the important role of 4-HBA in microbial cross talk, as 4-HBA strongly inhibits hyphal formation by Candida albicans. Together, our findings describe the dual roles of 4-HBA in both intraspecies signaling and interkingdom communication.

Inhibitory effects of Stevioside on Streptococcus mutans and Candida albicans dual-species biofilm.

Streptococcus mutans is the most prevalent biofilm-forming pathogen in dental caries, while Candida albicans is often detected in the presence of S. mutans. We aimed to evaluate the anti-caries effect of stevioside in medium trypticase soy broth (TSB) with or without sucrose supplementation compared with the same sweetness sucrose and xylitol in a dual-species model of S. mutans and C. albicans, based on planktonic growth, crystal violet assay, acid production, biofilm structural imaging, confocal laser scanning microscopy, and RNA sequencing. Our results showed that compared with sucrose, stevioside significantly inhibited planktonic growth and acid production, changed the structure of the mixed biofilm, and reduced the viability of biofilm and the production of extracellular polysaccharides in dual-species biofilm. Through RNA-seq, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway impact analysis showed that stevioside decreased sucrose metabolism and increased galactose and intracellular polysaccharide metabolism in S. mutans, and decreased genes related to GPI-modified proteins and secreted aspartyl proteinase (SAP) family in C. albicans. In contrast to xylitol, stevioside also inhibited the transformation of fungal morphology of C. albicans, which did not form mycelia and thus had reduced pathogenicity. Stevioside revealed a superior suppression of dual-species biofilm formation compared to sucrose and a similar anti-caries effect with xylitol. However, sucrose supplementation diminished the suppression of stevioside on S. mutans and C. albicans. Our study is the first to confirm that stevioside has anticariogenic effects on S. mutans and C. albicans in a dual-species biofilm. As a substitute for sucrose, it may help reduce the risk of developing dental caries.

Inhibitory effect of chlorogenic acid-grafted chitosan on seafood isolates Pseudomonas fluorescens and its biofilm.

This study aimed to examine the inhibition of chlorogenic acid-grafted chitosan (CS-g-CA) on Pseudomonas fluorescens (P. fluorescens) and its biofilm. The minimum inhibitory concentration (MIC) of CS-g-CA against P. fluorescens was 1.25mg/mL. Alkaline phosphatase (AKP) leak assay and scanning electron microscopy (SEM) indicted that CS-g-CA causes structural damage to cell walls and membranes, resulting in the loss of function. In addition, CS-g-CA was able to disrupt the antioxidant system of P. fluorescens, interfere with energy metabolism, and interact with genomic DNA, affecting the normal physiological function of bacteria. It was also found that CS-g-CA inhibited the flagellar motility of P. fluorescens, which may be responsible for the inhibition of its biofilm formation. CS-g-CA at 2MIC was able to remove 71.64% of the mature biofilm and reduce the production of extracellular polysaccharides (EPS) by 60.72%. This was further confirmed by confocal laser scanning microscopy (CLSM), which showed a significant reduction in the amount of biofilm. In summary, CS-g-CA has strong antibacterial and anti-biofilm activities against P. fluorescens, and it can be applied as a potential seafood bacteriostatic agent.

Resistance-driven innovations in the discovery of bactericides: novel triclosan derivatives decorating isopropanolamine moiety as promising anti-biofilm agents against destructive plant bacterial diseases.

Controlling bacterial infections in plants is a major challenge owing to the appearance of resistant strains. As a physical barrier, the bacterial biofilm helps bacterial infections acquire drug resistance by enabling bacteria to accommodate complex and volatile environmental conditions and avoid bactericidal effects. Thus, developing new antibacterial agents with antibiofilm potency is imperative. A series of simple triclosan derivatives containing isopropanolamine moiety were elaborately designed and assessed for their antibacterial behavior. Bioassay results showed that some title compounds had excellent bioactivity against three destructive bacteria Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac) and Pseudomonas syringae pv. actinidiae (Psa). Notably, compound C8 displayed high bioactivities toward Xoo and Xac, with EC50 values were 0.34 and 2.11 μg mL-1 , respectively. In vivo trials revealed that compound C8 exhibited excellent protective activities against rice bacterial blight and citrus bacterial canker at 200 μg mL-1 , with control effectivenesses of 49.57% and 85.60%, respectively. Compound A4 had remarkably inhibitory activity toward Psa, with an EC50 value of 2.63 μg mL-1 , and demonstrated outstanding protective activity with a value of 77.23% against Psa in vivo. Antibacterial mechanisms indicated that compound C8 dose-dependently prevented biofilm formation and extracellular polysaccharide production. C8 also significantly weakened the motility and pathogenicity of Xoo. This study contributes to the development and excavation of novel bactericidal candidates with broad-spectrum antibacterial activity by targeting bacterial biofilm to control refractory plant bacterial diseases. © 2023 Society of Chemical Industry.

Antibacterial and antibiofilm activities of Chinese propolis essential oil microemulsion against Streptococcus mutans.

To solve the shortcomings of poor solubility, easy volatilization, and decomposition, propolis essential oil microemulsion (PEOME) was prepared. The antibacterial, antibiofilm activities, and action mechanism of PEOME against Streptococcus mutans was analyzed. PEOME was prepared using anhydrous ethanol and Tween-80 as the cosurfactant and surfactant, respectively. The antibacterial activity of PEOME against S. mutans was evaluated using the agar disk diffusion method and broth microdilution method. The effects of PEOME on S. mutans biofilm was detected through the assays of crystal violet (CV), XTT reduction, lactic dehydrogenase (LDH) and calcium ions leaking, live/dead staining and scanning electron microscopy (SEM). And the antibiofilm mechanism of PEOME was elaborated by the assays of extracellular polysaccharide (EPS) production and glucosyltransferase (GTF) activity. The inhibition zone diameter (DIZ) of PEOME against S. mutans was 31mm, while the minimal inhibitory concentration (MIC) was 2.5μL mL-1. CV and XTT assays showed that PEOME could prevent fresh biofilm formation and disrupt preformed biofilm through decreasing the activities and biomass of biofilm. The leaking assays for LDH and calcium ions, as well as the live/dead staining assay, indicated that PEOME was able to damage the integrity of bacterial cell membranes within the biofilm. SEM revealed that PEOME had a noticeable inhibitory effect on bacterial adhesion and aggregation through observing the overall structure of biofilm. The assays of EPS production and GTF activity suggested that PEOME could reduce EPS production by inhibiting the activity of GTFs, thus showing an antibiofilm effect. The significant antibacterial and antibiofilm activities against S. mutans of PEOME meant that PEOME has great potential to be developed as a drug to prevent and cure dental caries caused by S. mutans.