EPS-producing Strains Research Articles

Bioconversion of sugar beet molasses into functional exopolysaccharides by beet juice-derived lactic acid bacteria

Sugar beet molasses, a sugar-rich byproduct of sugar beet industry, have great potential as a biorefinery feedstock for the production of value-added bio-products by microbial fermentation. The production of functional exopolysaccharides (EPS) by lactic acid bacteria (LAB) represents a promising strategy for valorizing sugar processing waste. This study screened and identified high-efficiency EPS-producing LAB isolates from beet juice. Among the 32 isolates, six LAB strains including Limosilactobacillus fermentum YL7, Lactiplantibacillus plantarum YL4, TC10, and CJ10, Leuconostoc mesenteroides TCT3 and TCT4, exhibited efficient bio-conversion of beet molasses to LAB-EPS, with yields varying from 13.96 to 22.26 g/L. Antioxidant activity analysis revealed that EPS from these strains displayed significant scavenging activities against ABTS+, DPPH, and -OH radicals. Notably, EPS produced by L. plantarum TC10 and L. fermentum YL7 exhibited superior ABTS + scavenging capacity, with rates up to 99.48% and 95.89% at 4 mg/mL, respectively. Additionally, EPS from strains YL4, YL7, TCT3 and TCT4 showed significant antibiofilm activity against S. aureus and E. coli, with EPS-YL7 inhibiting S. aureus biofilm formation by up to 90.49% at 8.0 mg/mL. Furthermore, EPS from strains TCT4 demonstrated great tolerance to digestive fluid compared to EPS from other strains, with a retention rate of 72% at the end of intestinal digestion. These findings suggest that EPS-producing LAB strains from beet juice can efficiently convert beet molasses into valuable EPS utilized as functional food ingredients.

Co-inoculation of biofilm- and exopolysaccharide-producing rhizobacteria promoting wheat development by boosting plant nutrients in a nutrient-limited soil

Increasing global land degradation and human population necessitate more agricultural production; therefore, plant cultivation may expand to nutrient-limited areas to meet growing food demands. As an environmentally safe application, plant growth-promoting rhizobacteria have a high potential to promote plant growth under stress conditions. The present study examined the impacts of single and co-inoculations of two high- and two low-biofilm- and exopolysaccharide (EPS)-producing Bacillus (B) and Azotobacter (A) strains on wheat growth in nutrient-limited soil. High- and low-biofilm-/EPS-producing strains were designated as + ve and − ve, respectively. Among the treatments applied, high-biofilm- and EPS-producing B (−) A (+) and B (+) A (−) treatments significantly enhanced shoot length by 20.4–24.5%, shoot fresh weight by 22.2–27.4%, root length by 31.4–37.1%, root fresh weight by 31.9–34.8%, and root dry weight by 27.2–31.4% over the non-inoculated control. Such two treatments also increased the uptake of nutrients (Ca, K, Mg, Fe, Cu, Mn, and Zn) by the roots more than almost all the other applications. A higher nutrient uptake enhanced the leaf chlorophyll contents and decreased antioxidant enzymes (catalase and peroxidase) activities in wheat seedlings exposed to the respective two treatments. The synergy between co-inoculated bacterial strains and their high-biofilm-/EPS-producing potential in B (−) A (+) and B (+) A (−) treatments appear to have a better role in enhanced wheat growth under nutrient stress by improving plant nutrient availability. The consortium of high-biofilm- and EPS-producing rhizobacteria may be used as potential bioinoculants to increase plant growth in nutrient-limited barren soils.

ANTIMICROBIAL, ANTIOXIDANT, AND OPTIMAL CONDITION FOR EXOPOLYSACCHARIDES SECRATED FROM NEW LOCAL STRAIN-ISOLATE Bifidobacterium longum subsp. infantis strain Iraq-Basrah 3

Metabolic products of exopolysaccharide (EPS) generated by LAB strains have several biomedical effects. Our study focused on the isolation of a new strain of Bifidobacterium spp. From the sources of children's feces, examining them to choose the best EPS-producing strain, studying all the optimal conditions to increase the efficiency of producing more EPS, knowing the stage of their production, and finally introducing them into biomedical applications to test their antimicrobial and antioxidant activities. EPS is secreted by the most efficient new local strain Bifidobacterium longum subsp. infantis strain Iraq-Basrah 3 was extracted and purified, resulting in the highest production (2.08±0.41 g/L) in 1% (w/v) starch, which is the best carbon source with the best inoculum size of 1% (v/v) in 18 h at 37 °C and a pH value of 6.5. Coinciding with the best production phase, the generation time for the new strain was 32.2 min, and maximum production occurred after 16 h (2,45 g/L) to 20 h (2.14 g/L) between the end of the logarithmic phase and the early stationary phase. EPS exhibited antimicrobial activity, where S. aureus (17.24±1.2 mm) and E. coli (16.6±0.94 mm) were immediately resistant to EPS. In contrast, other pathogens were resistant to EPS, whereas strong antioxidant activity was observed at a concentration of 1500 µg/ml (84.43±0.95%). Through this study, we have proven that optimal conditions directly affect the quantity and production of EPS and that it has an inhibitory effect on some microbes in addition to being a natural antioxidant for DPPH free radicals.

Characteristics of apricot yogurt fermented with different culture straıns and stevıa

This study evaluated the effects of exopolysaccharide (EPS)-producing and non-EPS-producing culture varieties and the enriching of apricot pulp to the post-acidification process and microbiological, viscosity, antioxidant, and sensory properties of yogurt. Two groups of yogurts were produced in terms of culture variety. One of the yogurts in both groups was enriched with apricot pulp at a ratio of 10%. The natural sweetener, stevia, was added at a ratio of 0.1% to all yogurts. The lowest pH and highest acidity values were determined for the non-EPS sample produced without apricot pulp. The dry matter content of the yogurts was increased with whey protein powder. Between the yogurts produced with EPS-producing strains, the bacteria counts were higher for those enriched with apricot pulp. The highest Streptococcus thermophilus counts were determined for the sample produced with EPS-producing culture and apricot pulp at the beginning and end of the storage. Total phenolic content (TPC) was higher for the samples produced with conventional culture and enriched with apricot pulp. Similar results were observed in the antioxidant activity. Sensory attributes were considered taste, odor, appearance, texture, and overall acceptability. The yogurts produced with EPS-producing culture were preferred regarding taste, texture, and overall acceptability.

Bacterial exopolysaccharide amendment improves the shelf life and functional efficacy of bioinoculant under salinity stress.

Bacterial exopolysaccharides (EPS) possess numerous properties beneficial for the growth of microbes and plants under hostile conditions. The study aimed to develop a bioformulation with bacterial EPS to enhance the bioinoculant's shelf life and functional efficacy under salinity stress. High EPS-producing and salt-tolerant bacterial strain (Bacillus haynessi SD2) exhibiting auxin-production, phosphate-solubilization, and biofilm-forming ability, was selected. EPS-based bioformulation of SD2 improved the growth of three legumes under salt stress, from which pigeonpea was selected for further experiments. SD2 improved the growth and lowered the accumulation of stress markers in plants under salt stress. Bioformulations with varying EPS concentrations (1% and 2%) were stored for 6 months at 4°C, 30°C, and 37°C to assess their shelf life and functional efficacy. The shelf life and efficacy of EPS-based bioformulation were sustained even after 6 months of storage at high temperature, enhancing pigeonpea growth under stress in both control and natural conditions. However, the efficacy of non EPS-based bioformulation declined following four months of storage. The bioformulation (with 1% EPS) modulated bacterial abundance in the plant's rhizosphere under stress conditions. The study brings forth a new strategy for developing next-generation bioformulations with higher shelf life and efficacy for salinity stress management in pigeonpea.

A methodological approach to assess the ropy character of stirred acid dairy gels based on the measure of adhesiveness.

This work aims to evaluate the potential and limits of adhesiveness measurement using a texturometer to assess the ropiness of acid dairy gels for starter selection. Commercial yogurts of various formulations and textures were used to assess the ability of adhesiveness to detect ropiness and to compare different probes' performance. Chemically acidified gels using different concentrations of glucono-delta-lactone (GDL) were tested to determine the effect of pH on adhesiveness. In addition, acidified (GDL) milk containing 3 EPS-producing adjunct strains were produced to evaluate the detection of ropy strains using adhesiveness, compared with an inoculation loop stretching test. The adhesiveness of commercial yogurts was mainly impacted by its formulation. Visually ropier commercial yogurts with high protein and fat contents presented higher adhesiveness. Globally, adhesiveness analysis was not impacted by probe material, but larger probes resulted in higher adhesiveness values. The addition of adjuncts increased the adhesiveness of GDL gels compared with the controls. Results between inoculation loop stretching test and adhesiveness were similar, except for Lactobacillus. delbrueckii lactis LMA-1511 which exhibited high adhesiveness but no threading with the loop stretching test. When varying GDL concentration, adhesiveness increased with decreasing pH until pH 4.45, and remained stable until pH 4.18. In the pH zone from 4.18 to 4.45, differences in adhesiveness could indicate the presence of a ropy strain. This method is promising for industries as a quality control or screening method for starter cultures due to its simplicity and the availability of texturometers.

Improving the Antioxidant and Anti-Inflammatory Activity of Fermented Milks with Exopolysaccharides-Producing Lactiplantibacillus plantarum Strains.

Exopolysaccharides (EPSs) producing lactic acid bacteria have been claimed to confer various health benefits to the host, including the ability to face oxidative and inflammatory-related stress. This study investigated the ability of food-borne Lactiplantibacillus (Lpb.) plantarum to improve the antioxidant activity of fermented milks by producing EPSs. Two Lpb. plantarum strains, selected as lower and higher EPSs producers, have been applied in lab-scale fermented milk production, in combination with conventional starters. Antioxidant activity was investigated in vitro using DPPH (1,1-diphenyl-2-picrylhydrazyl), ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), and FRAP (ferric reducing antioxidant power) assays while the ability to modulate reactive oxygen species (ROS) level was evaluated in an intestinal healthy model, subjected to both oxidative and inflammatory stress. Furthermore, to verify whether digestion affects functionality, fermented milks were evaluated before and after in vitro-simulated INFOGEST digestion. The results showed an improved antioxidant activity of fermented milk enriched with Lpb. plantarum LT100, the highest EPSs producer. Furthermore, the data showed a different ROS modulation with a protective anti-inflammatory effect of samples enriched with Lpb. plantarum strains. Our data suggest the use of selected EPS-producing strains of Lpb. plantarum as a natural strategy to enrich the functionality of fermented milks in terms of ROS modulation and inflammatory-related stress.

Effect of biogenic exopolysaccharides in characteristics and stability of a novel Requeson-type cheese

Whey is a by-product of the dairy industry with considerable nutritional value but tends to be discarded with industrial effluents. One of the alternatives for its use is the production of whey cheeses, although they need to add extra ingredients to raise the yields, which elevates production costs. A less expensive alternative is using exopolysaccharides (EPS), carbohydrate polymers microorganisms produce. This research aimed to formulate and evaluate the stability of a Requeson-type cheese employing whey that has EPS produced biogenically by in situ fermentation with lactic acid bacteria. Two EPS-producing strains, Lactobacillus delbrueckii subsp bulgaricus NCFB 2772 and Streptococcus thermophilus SY-102, were used separately and in coculture (1:1 ratio). We found that coculture had the highest EPS production (1.49 mg/mL of whey) compared to the monocultures. This influenced the yield of the processed Requeson-type cheese (5.56%), which was higher than the produced with unfermented whey (3.77%). Similarly, the physicochemical and sensory parameters of the developed product showed differences. Furthermore, none of the Requeson-type cheeses made with fermented whey showed microbial growth after 21 days of storage (4 °C). Therefore, EPS is a potential strategy for producing Requeson-type whey cheeses with a high yield and stability.

Structures, physical properties and antibacterial activity of silver nanoparticles of Lactiplantibacillus plantarum exopolysaccharide

Lactic acid bacteria (LAB) exopolysaccharide (EPS) has good water absorption, high viscosity, good stability, so it was widely used in probiotics fields. In this study, EPS-producing LAB strain Lactiplantibacillus plantarum HDL-03 was isolated and identified. Moreover, the HDL-03 EPS was used as a stabilizer and mixed with AgNO3 to synthesize a novel nanoparticle AgNPs whose structure and properties were explored. The monosaccharide composition and molecular weight indicated that HDL-03 EPS was a heteropolysaccharide composed of mannose and glucose. Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) spectroscopy analysis and methylation results jointly proved it was a heteropolysaccharide containing 1,3-Manp and 1,6-Glcp. The X-Ray diffraction (XRD) results showed that this EPS has an amorphous structure, while the synthesized AgNPs have crystalline properties. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results indicated EPS had a smooth and dense sheet structure, while the surface of AgNPs became rougher and large holes appeared after synthesis. Zeta particle size analysis suggested that the particle size of AgNPs increased by 36.63 nm compared to HDL-03 EPS. FT-IR analysis exhibited that the position of the characteristic peaks of AgNPs changed. The OH moving from a wavelength of 3388.49 cm−1 to a wavelength of 3316.79 cm−1 and telescopic vibration peak changed from 1356.07 cm−1 to 1344.22 cm−1. A plate inhibition test revealed the effect of different concentrations of EPS and AgNO3 synthesized AgNPs on the diameter of inhibition circle produced by the indicator bacteria Escherichia coli and Staphylococcus aureus. Furthermore, AgNPs were applied to the indicator bacteria, which the minimum inhibitory concentration (MIC), time-inhibitory curve, and changes in extracellular conductivity, nucleic acids, proteins, ATP, and lactate dehydrogenase (LDH) levels were determined. The AgNPs inhibited the growth of E. coli and S. aureus and exhibited outstanding antimicrobial properties. With the increase of treatment time, the degree of cell membrane damage increased, the permeability enhanced, and the intracellular substances leaked. These results indicate that HDL-03 EPS has good potential for applications in the production of food packaging, antimicrobials, catheters, textiles and coatings.

Efficient Screening and Enhanced Exopolysaccharide Production by Functional Lactic Acid Bacteria (LAB) in Lactose Supplemented Media

Exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) can be considered as natural biological thickeners that have attracted considerable attention in the food industry. This study aimed to evaluate and select potentially EPS-producing strains LAB and to assess the influence of carbon source and aeration on EPS production. Nine LAB strains were assessed as potential EPS producers, and Rahnella aquatilis ATCC 55046 was employed as the positive control strain for EPS. The compaction test and the observation of viscous colonies in a solid medium did not yield sufficient evidence for the presence of EPS. The assessment of capsules through staining provided evidence of EPS presence only for Rahnella aquatilis ATCC 55046. The EPS yield was subsequently assessed in De-Man Rogosa and Sharpe (MRS) broth medium supplemented with 2% (w/w) fructose (MRS-f) or lactose (MRS-l), as well as in whey (Whey) and whey supplemented with 2% (w/w) lactose (Whey-l). The EPS production in the various culture media under study ranged from 194 to 1,187 mg of EPS/g of polymer dry mass (PDM). These results suggest that the culture medium and carbon sources had an impact on the EPS production of the different strains. Bifidobacterium animalisBb12 achieved the highest EPS production in MRS-f. In the case of MRS-l, the control strain recorded the highest EPS value, along with Lactobacillus acidophilus LAC-1. Regarding Whey, Lentilactobacillus Kefir NCFB 2753 exhibited the highest EPS production, while in Whey-l, Lacticaseibacillus paracasei LCS-1 emerged as the top performer in terms of EPS production. This suggests that certain strains exhibit potential for use in the production of novel fermented EPS products, whether dairy or non-dairy.

A Ropy Exopolysaccharide-Producing Strain Bifidobacterium pseudocatenulatum Bi-OTA128 Alleviates Dextran Sulfate Sodium-Induced Colitis in Mice

Inflammatory bowel disease (IBD) is a chronic disease associated with overactive inflammation and gut dysbiosis. Owing to the beneficial effects of bifidobacteria on IBD treatment, this study aimed to investigate the anti-inflammation effects of an exopolysaccharide (EPS)-producing strain Bifidobacterium pseudocatenulatum Bi-OTA128 through a dextran sulfate sodium (DSS)-induced colitis mice model. B. pseudocatenulatum treatment improved DSS-induced colitis symptoms and maintained intestinal barrier integrity by up-regulating MUC2 and tight junctions’ expression. The oxidative stress was reduced after B. pseudocatenulatum treatment by increasing the antioxidant enzymes of SOD, CAT, and GSH-Px in colon tissues. Moreover, the overactive inflammatory responses were also inhibited by decreasing the pro-inflammatory cytokines of TNF-α, IL-1β, and IL-6, but increasing the anti-inflammatory cytokine of IL-10. The EPS-producing strain Bi-OTA128 showed better effects than that of a non-EPS-producing stain BLYR01-7 in modulating DSS-induced gut dysbiosis. The Bi-OTA128 treatment increased the relative abundance of beneficial bacteria Bifidobacterium and decreased the maleficent bacteria Escherichia-Shigella, Enterorhabuds, Enterobacter, and Osillibacter associated with intestinal inflammation. Notably, the genera Clostridium sensu stricto were only enriched in Bi-OTA128-treated mice, which could degrade polysaccharides to produce acetic acid and butyrate in the gut. This finding demonstrated a cross-feeding effect induced by the EPS-producing strain in gut microbiota. Collectively, these results highlighted the anti-inflammatory effects of the EPS-producing strain B. pseudocatenulatum Bi-OTA128 on DSS-induced colitis, which could be used as a candidate probiotic supporting recovery from ongoing colitis.

Encapsulating potential and functional properties of exopolysaccharide from Limosilactobacillus reuteri KCTC 14626BP isolated from human breast milk

Exopolysaccharides (EPS) are natural, nontoxic, biocompatible and biodegradable macromolecules produced by microorganisms, including the Lactic acid bacteria, to enhance protection against environmental stress conditions. The current study focused on the encapsulation and functional efficiency of EPS produced by probiotic strains isolated from human milk. Among 27 isolates, the potential high EPS-producing strain Limosilactobacillus reuteri KCTC 14626BP was selected based on biofilm production. The structural Characterization of EPS was performed based on FTIR, NMR and functional properties were determined; further, the encapsulation efficiency of EPS was determined with caffeic acid. The results indicate that L. reuteri produced EPS major component consisting of glucose, galactose and arabinose with the ratio of (0.78:0.16: 0.05). The antioxidant efficiency of EPS-LR was determined on DPPH (60.3 %) and ABTS (48.9 %); EPS showed enhanced functional activities. The absence of toxicity was confirmed based on Caenorhabditis elegans. The EPS-loaded Caffeic acid (CA) EPS-LR indicated spherical capsules with rough surfaces, with sizes ranging from 1.39 to 6.75 μm. These findings indicate that EPS-LR can be applied as a bioactive compound and encapsulating material in food, cosmetics, and pharmaceutical industries.

Bioprospecting for industrially relevant exopolysaccharide-producing cyanobacteria under Portuguese simulated climate

Cyanobacterial exopolysaccharides (EPS) are potential candidates for the production of sustainable biopolymers. Although the bioactive and physicochemical properties of cyanobacterial-based EPS are attractive, their commercial exploitation is limited by the high production costs. Bioprospecting and characterizing novel EPS-producing strains for industrially relevant conditions is key to facilitate their implementation in various biotechnological applications and fields. In the present work, we selected twenty-five Portuguese cyanobacterial strains from a diverse taxonomic range (including some genera studied for the first time) to be grown in diel light and temperature, simulating the Portuguese climate conditions, and evaluated their growth performance and proximal composition of macronutrients. Synechocystis and Cyanobium genera, from marine and freshwater origin, were highlighted as fast-growing (0.1–0.2 g L−1 day−1) with distinct biomass composition. Synechocystis sp. LEGE 07367 and Chroococcales cyanobacterium LEGE 19970, showed a production of 0.3 and 0.4 g L−1 of released polysaccharides (RPS). These were found to be glucan-based polymers with high molecular weight and a low number of monosaccharides than usually reported for cyanobacterial EPS. In addition, the absence of known cyanotoxins in these two RPS producers was also confirmed. This work provides the initial steps for the development of cyanobacterial EPS bioprocesses under the Portuguese climate.

Characterization of an EPS-producing bifidobacterial strain based on integration of phenotypic and complete genome sequencing data.

Bifidobacterium and Lactobacillus are known to be common members of the human intestinal microbiota, which play important roles in maintaining the homeostasis of host gut microenvironment. Several bifidobacterial and lactobacilli strains have been used as probiotics for health benefits. The exopolysaccharides (EPSs) produced by strains from Bifidobacterium and Lactobacillus are considered as beneficial traits mediating these beneficial effects. In this study, 21 strains belonging to Bifidobacterium and Lactobacillus were isolated from healthy infants' stool and were screened for EPS-producing ability. Among these strains, Bifidobacterium longum XZM1 showed the highest EPS productivity, which was further confirmed and characterized. The complete genome of strain XZM1 was sequenced, which revealed the presence of a gene cluster for EPS production. Furthermore, comparative genome analysis was performed among XZM1 and other strains from B. longum species. Following purification, the molecular weight (Mw) of EPS from XZM1 was determined as 4023Da (Mw) through gel permeation chromatography. Analysis of the EPS hydrolysates revealed that the EPS was composed of mannose, glucose, galactose, arabinose, and fucose. Additionally, the EPS exhibited higher scavenging abilities toward hydroxyl than 1,1-diphenyl-2-picrylhydrazyl free radical. Overall, these results suggest that XZM1 from B. longum species may be a promising probiotic candidate.

Purification and Identification of EPS Produced by Five Lactic Acid Bacteria and Evaluation of Their Effects on the Texture of Fermented Goat Milk

Extracellular polysaccharide (EPS) produced by five lactic acid bacteria (Limosilactobacillus fermentum B55, Limosilactobacillus fermentum B62, Lactiplantibacillus plantarum 7830, Pediococcus acidilactici B30, and Lactobacillus helveticus K2) were purified and identified, and their effects on the texture of fermented goat milk were evaluated. The purified EPS fractions EPS 1a, EPS 2b, EPS 3c, EPS 4d, and EPS 5e of strains B62, 7830, K2, B55, and B30 were obtained with ion exchange chromatography, and their molecular weights were 2.41 × 104, 1.62 × 104, 6.42 × 103, 6.45 × 103, and 1.26 × 104 Da, found using gel permeation chromatography. The infrared spectrum results showed that these substances all contained polysaccharide characteristic absorption peaks, most of which contained O-H bonds, C-H bonds, hydroxyl and carboxyl bonds, and groups. The analysis of monosaccharide composition presented that EPS1a was composed of guluronic acid, rhamnose, and galactose, with a molar ratio of 2.7:1:2.4; EPS2b and EPS3c were composed of guluronic acid; EPS4d was composed of guluronic acid, glucose, and galactose, with a molar ratio of 1:1.1:1.2; and EPS5e was composed of glucose and galactose, with a molar ratio of 1.6:1, indicating the differences in the composition and structure of EPS produced by various strains. Compared with the control group that only had the starter added, adding EPS-producing strains could promote acid production and improve the texture of fermented goat milk, and its acidity, hardness, consistency, viscosity, and viscosity index were higher.

Improving drought tolerance and glycyrrhizin content of licorice plant by EPS-producing cyanobacteria

We evaluated the effects of two selected EPS-producing cyanobacterial strains for microbe-dependent drought tolerance in native licorice plant (Glycyrrhiza glabra) and addressed the mechanisms, which might be improved through these interactions. These bacteria were inoculated on the soils in a form of single strain (Anabaena sphaerica or Nostoc pruniforme) or two strains (Anabaena + Nostoc) in greenhouse conditions. The growth parameters, physiological and metabolical responses among treatments were investigated through assaying the antioxidants and glycyrrhizin contents in the plants grown in both normal condition and moderate water stress condition (FC 50%). The reduction of the ratio of root/shoot in response to drought (FC 50%) was correlated with amount of specific metabolites production, including glycyrrhizic acid (GA), glabridin (GB), liquiritin (LQ) and liquiritigenin (LG), especially in soil treated by Anabaena + Nostoc (P < 0.05). In water-deficient conditions, accumulation of GA in plants treared by Anabaena + Nostoc was boosted by 64% and 69% compared to Anabaena and the control, respectively. Besides, a significant increase in catalase activity (25%) was perceived in this treatment after exposure to drought stress. These results highlight the potential role of enzymatic antioxidants and the increase of GA content in responsing to the drought tolerance in licorice plant. Our findings suggest that using EPS-producing strains of Cyanobacteria is an efficient treatment to improve the drought tolerance in cultivation of medicinal plant in soil of arid and semi-arid regions.

Contribution of the capsular polysaccharide layer to antibiotic resistance in bifidobacteria.

Bifidobacteria have been shown to produce exopolysaccharides (EPS), which are polymeric structures composed of various carbohydrates, commonly containing glucose, galactose, and rhamnose. EPS are produced by different bifidobacterial taxa commonly identified in the human gut, such as Bifidobacterium breve and Bifidobacterium longum subsp. longum, and have been suggested to modulate the interaction of bifidobacterial cells with other members of the human gut microbiota as well as with their host. In this study, we evaluated if bifidobacterial EPS production of four selected EPS-producing strains is associated with enhanced resistance to antibiotic treatments through MIC analysis when compared to bacterial cultures that do not produce exopolysaccharides. Our results showed that an increase in EPS production by modifying the growth medium with different carbon sources, i.e. glucose, galactose or lactose and/or by applying stressful conditions, such as bile salts and acidity, is associated with a tolerance enhancement of bifidobacterial cells toward various beta-lactam antibiotics. In addition, after analyzing the production of EPS at the phenotypic level, we explored the genes involved in the production of these structures and evaluated their expression, in presence of various carbon sources, using RNAseq. Overall, this study provides preliminary experimental evidence showing how bifidobacterial EPS modifies the level of susceptibility of these bacteria towards antibiotics.

Exopolysaccharide-producing Lacticaseibacillus paracasei strains isolated from kefir as starter for functional dairy products.

Exopolysaccharides (EPS) produced by lactic acid bacteria are molecules of great interest for the dairy food industry. Lacticaseibacillus paracasei CIDCA 8339, CIDCA 83123, and CIDCA 83124 are potentially probiotic strains isolated from kefir grains whose EPS-production on MRS broth is dependent on incubation temperature. The aim of the present work is to evaluate the effect of fermentation temperature on the characteristics of EPS produced in milk by L. paracasei strains and the consequent impact on the rheological properties of the fermented products. Additionally, the protective effect of these EPS against Salmonella infection was evaluated in vitro. Acid gels with each strain were obtained by milk fermentation at 20°C, 30°C, and 37°C evidencing for all the strains a reduction in growth and acidification rate at lower temperature. Lacticaseibacillus paracasei CIDCA 83123 showed low fermentation rate at all temperatures requiring between 3 and 8 days to obtain acids gels, whereas CIDCA 8339 and 83124 needed between 24 and 48 h even when the temperature was 20°C. Fermentation temperature led to changes in crude EPS characteristics of the three strains, observing an increase in the relative amount of the high molecular weight fraction when the fermentation temperature diminished. Additionally, EPS83124 and EPS83123 presented modifications in monosaccharide composition, with a reduction of rhamnose and an increase of amino-sugars as temperature rise. These changes in the structure of EPS83124 resulted in an increase of the apparent viscosity of milks fermented at 20°C (223 mPa.s) and 30°C (217 mPa.s) with respect to acid gels obtained at 37°C (167 mPa.s). In order to deepen the knowledge on EPS characteristics, monosaccharide composition of low and high molecular weight EPS fractions were evaluated. Finally, it was evidenced that the preincubation of intestinal epithelial cells Caco-2/TC-7 with EPS8339 and EPS83124 partially inhibit the association and invasion of Salmonella. In light of these results, it can be concluded that the selection of the EPS-producing strain along with the appropriate fermentation conditions could be an interesting strategy to improve the technological properties of these L. paracasei fermented milks with potential protective effects against intestinal pathogens.

Isolation and Identification of New Soil Strains with Phosphate-Solubilizing and Exopolysaccharide-Producing Abilities in the Yellow River Wetland Nature Reserve of Luoyang City, China

The establishment of the Yellow River wetland nature reserves improves the local soil structure and fertility through the long-term succession of microorganisms. However, little is known about which indigenous microbial resources can accelerate the process of soil improvement and ecology restoration. To fill this gap, exopolysaccharides-producing bacteria and phosphate-solubilizing bacteria were isolated from soil samples of the wetland nature reserve with higher soil organic matter, available phosphorus, and available nitrogen content. 16S rRNA nucleotide sequence homology analysis and physiological-biochemical assay showed that the strain PD12 with the highest phosphate solubilization activity and higher EPS production was identified as Klebsiella variicola, and other high yield EPS-producing strains (EPS12, EPS15, EPS18, and EPS19) were identified as Pseudomonas migulae, Pseudomonas frederiksbergensis, Aeromonas media, and Pseudomonas vancouverensis, respectively. These results provided new potential microbial resources for the research and development of biofertilizers and added new insights into accelerating the restoration of physical, chemical, and biological properties of soil in the Yellow River basin.

Structural characterization and partial properties of dextran produced by Leuconostoc mesenteroides RSG7 from pepino.

Exopolysaccharides (EPSs) produced by lactic acid bacteria possess various bioactivities and potential attractions for scientific exploration and commercial development. An EPS-producing bacterial strain, RSG7, was previously isolated from the pepino and identified as Leuconostoc mesenteroides. Based on the analyses of high-performance size exclusion chromatography, high-performance ion chromatography, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and methylation, the RSG7 EPS was identified as a dextran with a molecular weight of 5.47 × 106 Da and consisted of α-(1→6) glycosidic linkages as backbone and α-(1→2), α-(1→3), α-(1→4), and α-(1→6) glycosidic linkages as side chains. Scanning electron microscopy observed a honeycomb-like porous structure of RSG7 dextran, and this dextran formed aggregations with irregular hill-shaped lumps according to atomic force microscopy analysis. Physical-chemical investigations suggested that RSG7 dextran possessed excellent viscosity at high concentration, low temperature, and high pH; showed a superior emulsifying capacity of tested vegetable oils than that of hydrocarbons; and owned the maximal flocculating activity (10.74 ± 0.23) and flocculating rate (93.46 ± 0.07%) in the suspended solid of activated carbon. In addition, the dextran could coagulate sucrose-supplemented milk and implied potential probiotics in vitro. Together, these results collectively describe a valuable dextran with unique characteristics for exploitation in food applications.