New Levan-Type Exopolysaccharide from Bacillus amyloliquefaciens as an Antiadhesive Agent against Enterotoxigenic Escherichia coli

A glucomannan produced by Bacillus velezensis HY23 and its growth promoting effect on soybeans under salt stress

The Bacillus genus is widely distributed in nature, has bacteriostatic and growth-promoting activities, and has broad application potential in agriculture. An exopolysaccharide (EPS) was extracted and purified from Bacillus velezensis HY23. Structural characterisation of the EPS was performed by chemical and spectroscopic analyses. Methylation analysis showed that the EPS of HY23 was composed of mannose and glucose at a ratio of 82:18 and was identified as glucomannan. Combined with the nuclear magnetic resonance (NMR) analysis, EPS from HY23 had a backbone of →2)-α-D-Manp-(1 → and →2,6)-α-D-Manp-(1 → branched at C-6 with terminal α-(3-O-Me)-D-Manp-(1 → and →6)-α-D-Manp-(1 → residues as the side chain. A certain amount of β-D-Glcp residues were also present in backbone. Moreover, EPS significantly improved the nitrogen-fixing activity and salt resistance of soybean seedlings by regulating the antioxidant pool and expression of ion transporters. These findings indicate that EPS from B. velezensis HY23 is a potential biostimulant for enhancing plant resistance to salt stress.

Dextran and levan exopolysaccharides from tempeh-associated lactic acid bacteria with bioactivity against enterotoxigenic Escherichia coli (ETEC)

Soybean tempeh contains bioactive carbohydrate that can reduce the severity of diarrhea by inhibiting enterotoxigenic Escherichia coli (ETEC) adhesion to mammalian epithelial cells. Lactic acid bacteria (LAB) are known to be present abundantly in soybean tempeh. Some LAB species can produce exopolysaccharides (EPS) with anti-adhesion bioactivity against ETEC but there has been no report of anti-adhesion bioactive EPS from tempeh-associated LAB. We isolated EPS-producing LAB from tempeh-related sources, identified them, unambiguously elucidated their EPS structure and assessed the bioactivity of their EPS against ETEC. Pediococcus pentosaceus TL, Leuconostoc mesenteroides WA and L. mesenteroides WN produced both dextran (α-1,6 linked glucan; >1000 kDa) and levan (β-2,6 linked fructan; 650-760 kDa) in varying amounts and Leuconostoc citreum TR produced gel-forming α-1,6-mixed linkage dextran (829 kDa). All four isolates produced EPS that could adhere to ETEC cells and inhibit auto-aggregation of ETEC. EPS-PpTL, EPS-LmWA and EPS-LmWN were more bioactive towards pig-associated ETEC K88 while EPS-LcTR was more bioactive against human-associated ETEC H10407. Our finding is the first to report on the bioactivity of dextran against ETEC. Tempeh is a promising source of LAB isolates that can produce bioactive EPS against ETEC adhesion and aggregation.

Characterization of a novel exopolysaccharide from Acinetobacter rhizosphaerae with ability to enhance the salt stress resistance of rice seedlings

We here describe the isolation of a novel exopolysaccharide from Acinetobacter rhizosphaerae, named ArEPS. The structure of ArEPS was characterized by analysis of the monosaccharide composition, molecular weight, infrared spectrum, methylation, and nuclear magnetic resonance spectrum. ArEPS was found to be an acidic heteropolysaccharide composed of glucose, galactose, galacturonic acid, glucuronic acid, mannose, and glucosamine; the molecular weight was 1533 kDa. Structural analysis showed that the main-chain structure of ArEPS predominantly comprised 1,3,6-β-Glcp, 1,3,4-α-Galp, 1,2-β-Glcp, 1,4-β-GlcpA, 1,4-β-GalpA, and the side-chain structure comprised 1,6-β-Glcp, 1,3-β-Galp, 1-α-Glcp, 1-β-Galp, 1-α-Manp, 1,4,6-α-Glcp, 1,2,4-β-Glcp, 1,2,3-β-Glcp, and 1,3-β-GlcpN. ArEPS significantly enhanced the tolerance of rice seedlings to salt stress. Specifically, plant height, fresh weight, chlorophyll content, and the K+/Na+ ratio increased by 51 %, 63 %, 29 %, and 162 %, respectively, and the malondialdehyde content was reduced by 45 % after treatment with 100 mg/kg ArEPS compared to treatment with 100 mM NaCl. Finally, based on the quadratic regression between fresh weight and ArEPS addition, the optimal ArEPS addition level was estimated to be 135.12 mg/kg. These results indicate the prospects of ArEPS application in agriculture.

Recent advances and prospects of Bacillus amyloliquefaciens as microbial cell factories: from rational design to industrial applications

Bacillus amyloliquefaciens is one of the most characterized Gram-positive bacteria. This species has unique characteristics that are beneficial for industrial applications, including its utilization of: cheap carbon as a substrate, a transparent genetic background, and large-scale robustness in fermentation. Indeed, the productivity characteristics of B. amyloliquefaciens have been thoroughly analyzed and further optimized through systems biology and synthetic biology techniques. Following the analysis of multiple engineering design strategies, B. amyloliquefaciens is now considered an efficient cell factory capable of producing large quantities of multiple products from various raw materials. In this review, we discuss the significant potential advantages offered by B. amyloliquefaciens as a platform for metabolic engineering and industrial applications. In addition, we systematically summarize the recent laboratory research and industrial application of B. amyloliquefaciens, including: relevant advances in systems and synthetic biology, various strategies adopted to improve the cellular performances of synthetic chemicals, as well as the latest progress in the synthesis of certain important products by B. amyloliquefaciens. Finally, we propose the current challenges and essential strategies to usher in an era of broader B. amyloliquefaciens use as microbial cell factories.

Advanced strategies for metabolic engineering of Bacillus to produce extracellular polymeric substances

Extracellular polymeric substances are mainly synthesized via a variety of biosynthetic pathways in bacteria. Bacilli-sourced extracellular polymeric substances, such as exopolysaccharides (EPS) and poly-γ-glutamic acid (γ-PGA), can serve as active ingredients and hydrogels, and have other important industrial applications. However, the functional diversity and widespread applications of these extracellular polymeric substances, are hampered by their low yields and high costs. Biosynthesis of extracellular polymeric substances is very complex in Bacillus, and there is no detailed elucidation of the reactions and regulations among various metabolic pathways. Therefore, a better understanding of the metabolic mechanisms is required to broaden the functions and increase the yield of extracellular polymeric substances. This review systematically summarizes the biosynthesis and metabolic mechanisms of extracellular polymeric substances in Bacillus, providing an in-depth understanding of the relationships between EPS and γ-PGA synthesis. This review provides a better clarification of Bacillus metabolic mechanisms during extracellular polymeric substance secretion and thus benefits their application and commercialization.

Characterization and bioactivities of exopolysaccharide produced from Azotobacter salinestris EPS-AZ-6

This study involved the extraction of an exopolysaccharide (EPS) from Azotobacter salinestris AZ-6, which was isolated from soil cultivated with leguminous plants. In a medium devoid of nitrogen, the AZ-6 strain displayed a maximum EPS yield of 1.1 g/l and the highest relative viscosity value of 3.4. The homogeneity of the polymer was demonstrated by the average molecular weight of 1.61 × 106 Da and a retention time of 17.211 min for levan. The presence of characteristic functional groups and structural units of carbohydrate polymers has been confirmed through spectroscopic analyses utilizing Fourier-transform infrared (FT-IR) and nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) revealed a noteworthy decrease in weight (74 %) in the temperature range spanning from 260 to 350 °C. X-ray diffraction (XRD) was utilized to verify the crystalline and amorphous characteristics of EPS-AZ-6. The EPS-AZ-6 exhibited significant cytotoxicity against the MCF-7 tumor cell line, as evidenced by an IC50 value of 6.39 ± 0.05 μg/ml. It also demonstrated a moderate degree of cytotoxicity towards HepG-2 cell line, as indicated by an IC50 value of 29.79 ± 0.41 μg/ml. EPS-AZ-6 exhibited potent antioxidant and in vitro antibacterial properties. These characteristics suggest the potential application value of EPS-AZ-6 in the food industry and pharmaceutical applications.

Production and Characterisation of an Exopolysaccharide by Bacillus amyloliquefaciens: Biotechnological Applications

The Bacillus amyloliquefaciens RT7 strain was isolated from an extreme acidic environment and identified. The biodegradation capabilities of the strain using different carbon sources (glucose, oleic acid, Tween 80, PEG 200, and the combination of glucose-Tween 80) were evaluated via an indirect impedance technique. The glucose-Tween 80 combination was further studied using nuclear magnetic resonance (NMR). The exopolysaccharide (EPS_RT7) that had been produced with the strain when biodegrading glucose-Tween 80 was isolated and characterised using different techniques (GC-MS, HPLC/MSMS, ATR-FTIR, TGA, and DSC), and its molecular weight was estimated. The results show that the average molecular weight of EPS_RT7 was approximately 7.0794 × 10⁴ Da and a heteropolysaccharide composed of mannose, glucose, galactose, and xylose (molar ratio, 1:0.5:0.1:0.1) with good thermostability. EPS_RT7 showed good emulsifying activity against different natural oils and hydrocarbons at high concentrations (2 mg/mL) and at the studied pH range (3.1-7.2). It also presented good emulsifying activity compared to that of commercial emulsifiers. Lastly, EPS_RT7 showed antioxidant capacity for different free radicals, a lack of cytotoxicity, and antioxidant activity at the cellular level. EPS_RT7 has promising applications in bioremediation processes and other industrial applications.

Biological properties of exopolysaccharides produced by Bacillus spp

There is currently a constant search for ecofriendly bioproducts, which could contribute to various biomedical applications. Among bioproducts, exopolysaccharides are prominent contemporary extracellular biopolymers that are produced by a great variety of bacterial species. These homo- or heteropolymers are composed of monomeric sugar units linked by glycosidic bonds, which are secreted to the external medium. Bacillus spp. are reported to be present in different ecosystems and produce exopolysaccharides with different biological properties such as antioxidant, antibacterial, antiviral anti-inflammatory, among others. Since a great diversity of bacterial strains are able to produce exopolysaccharides, a great variation in the molecular composition is observed, which is indeed present in some of the chemical structures predicted until date. These molecular characteristics and their relations with different biological functions are discussed in order to visualize future applications in biomedical section.

Simulated Digestion and Fecal Fermentation Behaviors of Levan and Its Impacts on the Gut Microbiota

Levan is a microbial fructan widely explored in various fields owing to its excellent physical and biochemical properties. However, little is known about its digestion and fermentation characteristics in vitro. This study evaluated the potential prebiotic properties of levan obtained by enzymatic synthesis. Scanning electron microscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy showed that the primary structures of levan remained stable after saliva-gastrointestinal digestion. The microtopography, molecular weight, and functional group of levan were seriously damaged during fecal fermentation. Moreover, the total short-chain fatty acid levels increased significantly, especially for propionic acid, butyric acid, and valeric acid. The 16S rDNA sequencing showed that levan mainly increased the abundance of Firmicutes; in genus levels, certain beneficial bacteria such as Megasphaera and Megamonas genera were remarkably promoted, and the proliferation of harmful genera was inhibited (such as Cedecea and Klebsiella). Overall, this study provided new insights into the potential probiotic mechanism of levan.

Bacillus-derived probiotics: metabolites and mechanisms involved in bacteria-host interactions

Bacillus probiotics have a sporulation capacity that makes them more suitable for processing and storage and for surviving passage through the gastrointestinal tract. The probiotic functions and regulatory mechanisms of different Bacillus have been exploited in many reports, but little is known about how various Bacillus probiotics perform different functions. This knowledge gap results in a lack of specificity in the selection and application of Bacillus. The probiotic properties are strain-specific and cell-type-specific, and are related to the germination potential and to the diversity of metabolites produced following intestinal germination, as this causes the variation in probiotic function and mechanisms. In this review, we discuss the Bacillus metabolites produced during germination and sporulation in the GI tract, as well as possible processes affecting intestinal homeostasis. We conclude that the oxygen-capturing capability and the production of antimicrobials, exoenzymes, competence and sporulation factors (CSF), exopolysaccharides, lactic acid, and cell components are specifically associated with the functional mechanisms of probiotic Bacillus. The aim of this review is to guide the screening of potential Bacillus strains for probiotics and their application in nutrition research. The information provided will also promote further research on Bacillus-derived functional metabolites in human nutrition.

Barley Husk Degraded by Fusarium graminearum MH1 Induced Premature Yeast Flocculation

Premature yeast flocculation (PYF) is one of the pivotal problems affecting beer flavor and production. PYF is induced by certain non-starch polysaccharides produced by the degradation of malted barley husks upon the growth of contaminated microorganisms, such as Fusarium graminearum. In this research, the formation mechanism of PYF was uncovered by investigating the secretome of F. graminearum MH1 inoculated to the barley husk. The polysaccharide extract of degraded husk was ultrafiltrated into four fractions and characterized by the minimum PYF concentration, molecular mass distribution, monosaccharide composition, and zeta potential. Among the four fractions, the high-molecular-weight polysaccharide fraction had the highest content of uronic acid and the most negative zeta potential, which contributed to the most severe PYF phenomenon. In addition, the PYF yeast showed a more negative zeta potential than the control yeast during the small-scale brewing process. This is aligned to the negatively charged polysaccharides potentially bonded to the surface of yeast cells through the calcium cation in the same fermentation system, which results in rapid flocculation and precipitation. Approximately 12% of the 214 proteins identified in the Fusarium graminearum MH1 secretome were hemicellulases, which substantially interpreted the mechanism of polysaccharides inducing PYF yeast during beer brewing.

Production of levan from Bacillus subtilis var. natto and apoptotic effect on SH-SY5Y neuroblastoma cells

Levan is a high-valued polysaccharide of fructose produced by several microbial species. These polysaccharides have been described as effective therapeutic agents in some human disease conditions, such as cancer, heart diseases and diabetes. The objective of this study was to examine the effect of levan (β-(2 → 6)-fructan) produced through sucrose fermentation by B. subtilis var. natto on the proliferation rate, cytotoxicity, and apoptosis of human neuroblastoma SH-SY5Y cells. It was obtained 41.44 g/L of levan in 18 h by biotechnological fermentation and SH-SY5Y cells were exposed to 1000 μg/mL of levan. The treatment with 1000 μg/mL of levan induced apoptosis in SH-SY5Y cancer cells by the significant increase in Annexin V/7-AAD and caspase 3/7 activation, but did not decrease proliferation or triggered a cytotoxic effect. 1000 μg/mL levan treatment is a promising therapeutic strategy for SH-SY5Y neuroblastoma cells.

Preventive effect of Bacillus mojavensis levan against carbon tetrachloride and cisplatin toxicity: in vivo study

This study is the first to investigate the hepato- and nephron-preventive effect of levan from Bacillus mojavensis (BM-levan) against toxicity induced by carbon tetrachloride (CCl₄) and cisplatin. Thirty-six male albino rats weighing between 230 and 250 g were used for this experiment. The groups received multiples doses of BM-levan and were compared to the untreated group. The in vitro and in vivo biological potentials of BM-levan were evaluated by measuring its antioxidant capacity as well as its hepato- and nephron-protective activities in rat models. The investigations highlighted a significant in vitro antioxidant activity indicated by the radical-scavenging capacity, the reducing power, and the total antioxidant activity measurement. In addition, results demonstrate that BM-levan supplementation during 8 weeks (100 mg/kg body weight) significantly (p < 0.05) decreased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities and remarkably (p < 0.05) attenuated the altered lipid profile by decreasing the levels of triglycerides (TG) and total cholesterol (TC), LDL cholesterol (LDL-C) and by enhancing the HDL cholesterol (HDL-C) content, when compared with the CCl₄ group. BM-levan also reduced the content of plasma renal biomarkers (urea, creatinine, and uric acid) in the cisplatin-treated group. Moreover, BM-levan inhibited hepatic and renal oxidative stress generated by CCl₄ and cisplatin administration, through the enhancement of the antioxidant catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) and the diminishment of lipid peroxidation. The harmful effects of CCl₄ or cisplatin on hepatic and renal histology were found to be decreased by the addition of BM-levan. Therefore, BM-levan has proved promising for biomedical applications thanks to its in vitro and in vivo antioxidant properties.

Biomedical Applications of Bacterial Exopolysaccharides: A Review

Bacterial exopolysaccharides (EPSs) are an essential group of compounds secreted by bacteria. These versatile EPSs are utilized individually or in combination with different materials for a broad range of biomedical field functions. The various applications can be explained by the vast number of derivatives with useful properties that can be controlled. This review offers insight on the current research trend of nine commonly used EPSs, their biosynthesis pathways, their characteristics, and the biomedical applications of these relevant bioproducts.

Prebiotic, Probiotic, Antimicrobial, and Functional Food Applications of Bacillus amyloliquefaciens

Bacillus amyloliquefaciens belongs to the genus Bacillus and family Baciliaceae. It is ubiquitously found in food, plants, animals, soil, and in different environments. In this review, the application of B. amyloliquefaciens in probiotic and prebiotic microbes in fermentation, synthesis, and hydrolysis of food compounds is discussed as well as further insights into its potential application and gaps. B. amyloliquefaciens is also a potential microbe in the synthesis of bioactive compounds including peptides and exopolysaccharides. In addition, it can synthesize antimicrobial compounds (e.g., Fengycin, and Bacillomycin Lb), which makes its novelty in the food sector greater. Moreover, it imparts and improves the functional, sensory, and shelf life of the end products. The hydrolysis of complex compounds including insoluble proteins, carbohydrates, fibers, hemicellulose, and lignans also shows that B. amyloliquefaciens is a multifunctional and potential microbe which can be applied in the food industry and in functional food processing.

Ultrasonic-assisted enzymatic extraction of Sparassis crispa polysaccharides possessing protective ability against H2O2-induced oxidative damage in mouse hippocampal HT22 cells

Extraction optimization, structural characterization, and neuroprotective effects of polysaccharides from Sparassis crispa.

Levan from Bacillus amyloliquefaciens JN4 acts as a prebiotic for enhancing the intestinal adhesion capacity of Lactobacillus reuteri JN101

Improving intrinsic adhesion performance of the known probiotics facilitates their residence and colonization, and therefore exerts more beneficial effects on the human or animal host. In this study, through adaptive culture with levan, Lactobacillus reuteri JN101 achieved the same biomass and exhibited 2.6 times higher adhesion capacity to HT-29 cells than those grown with glucose. The mechanism study related to this adhesion enhancement showed that the elevated proportion of unsaturated fatty acids facilitated the bacterial cells to overcome repulsive forces to approach the intestinal epithelial cell. At the same time, and the greater amounts of cell membrane proteins, such as S-layer protein (3.2 folds), elongation factor Tu (2.6 folds) and phosphoglycerate kinase (2.4 folds) probably enhanced the complementary interactions to the receptor on the epithelial cell. These results presented here indicated levan could be used as a potential prebiotic to regulate the adhesion capacity of probiotics, and provide ground for developing the specific-probiotics oriented functional food.