Gentio-oligosaccharides from Leuconostoc mesenteroides NRRL B-1426 dextransucrase as prebiotics and as a supplement for functional foods with anti-cancer properties

Kinetics and products of Thermotoga maritima β-glucosidase with lactose and cellobiose

Galacto-oligosaccharides (GOS) are prebiotic compounds that are mainly used in infant formula to mimic bifidogenic effects of mother's milk. They are synthesized by β-galactosidase enzymes in a trans-glycosylation reaction with lactose. Many β-galactosidase enzymes from different sources have been studied, resulting in varying GOS product compositions and yields. The in vivo role of these enzymes is in lactose hydrolysis. Therefore, the best GOS yields were achieved at high lactose concentrations up to 60%wt, which require a relatively high temperature to dissolve. Some thermostable β-glucosidase enzymes from thermophilic bacteria are also capable of using lactose or para nitrophenyl-galactose as a substrate. Here, we describe the use of the β-glucosidase BglA from Thermotoga maritima for synthesis of oligosaccharides derived from lactose and cellobiose and their detailed structural characterization. Also, the BglA enzyme kinetics and yields were determined, showing highest productivity at higher lactose and cellobiose concentrations. The BglA trans-glycosylation/hydrolysis ratio was higher with 57%wt lactose than with a nearly saturated cellobiose (20%wt) solution. The yield of GOS was very high, reaching 72.1%wt GOS from lactose. Structural elucidation of the products showed mainly β(1 → 3) and β(1 → 6) elongating activity, but also some β(1 → 4) elongation was observed. The β-glucosidase BglA from T. maritima was shown to be a very versatile enzyme, producing high yields of oligosaccharides, particularly GOS from lactose. KEY POINTS: • β-Glucosidase of Thermotoga maritima synthesizes GOS from lactose at very high yield. • Thermotoga maritima β-glucosidase has high activity and high thermostability. • Thermotoga maritima β-glucosidase GOS contains mainly (β1-3) and (β1-6) linkages.

Gluco-oligosaccharides as potential prebiotics: Synthesis, purification, structural characterization, and evaluation of prebiotic effect

Prebiotics have long been used to modulate the gut microbiota and improve host health. Most established prebiotics are nondigestible carbohydrates, especially short-chain oligosaccharides. Recently, gluco-oligosaccharides (GlcOS) with 2-10 glucose residues and one or more O-glycosidic linkage(s) have been found to exert prebiotic potentials (not fully established prebiotics) because of their selective fermentation by beneficial gut bacteria. However, the prebiotic effects (non-digestibility, selective fermentability, and potential health effects) of GlcOS are highly variable due to their complex structure originating from different synthesis processes. The relationship between GlcOS structure and their potential prebiotic effects has not been fully understood. To date, a comprehensive summary of the knowledge of GlcOS is still missing. Therefore, this review provides an overview of GlcOS as potential prebiotics, covering their synthesis, purification, structural characterization, and prebiotic effect evaluation. First, GlcOS with different structures are introduced. Then, the enzymatic and chemical processes for GlcOS synthesis are critically reviewed, including reaction mechanisms, substrates, catalysts, the structures of resultant GlcOS, and the synthetic performance (yield and selectivity). Industrial separation techniques for GlcOS purification and structural characterization methods are discussed in detail. Finally, in vitro and in vivo studies to evaluate the non-digestibility, selective fermentability, and associated health effects of different GlcOS are extensively reviewed with a special focus on the GlcOS structure-function relationship.

Synergistic Immunostimulatory Activities of Probiotic Strains, Leuconostoc lactis and Weissella cibaria, and the Prebiotic Oligosaccharides They Produce

Synbiotics contain health-beneficial bacteria, i.e., probiotics and prebiotics selectively utilized by the probiotics. Herein, three probiotic strains, Leuconostoc lactis CCK940, L. lactis SBC001, and Weissella cibaria YRK005, and the oligosaccharides produced by these strains (CCK, SBC, and YRK, respectively) were used to prepare nine synbiotic combinations. Macrophages (RAW 264.7) were treated with these synbiotic combinations and the corresponding lactic acid bacteria and oligosaccharides alone to evaluate the treatments' immunostimulatory activities. The level of nitric oxide (NO) production was significantly higher in the macrophages treated with the synbiotics than in those treated with the corresponding probiotic strains and the oligosaccharide alone. The immunostimulatory activities of the synbiotics increased regardless of the probiotic strain and the type of oligosaccharide used. The expressions of tissue necrosis factor-α, interleukin-1β, cyclooxygenase-2, inducible NO synthase genes, and extracellular-signal-regulated and c-Jun N-terminal kinases were significantly higher in the macrophages treated with the three synbiotics than in those treated with the corresponding strains or with the oligosaccharides alone. These results indicate that the synergistic immunostimulatory activities of probiotics and the prebiotics they produced in the studied synbiotic preparations resulted from the activation of the mitogen-activated protein-kinase-signaling pathway. This study suggests the combined use of these probiotics and prebiotics in the development of synbiotic preparations as health supplements.

Utilisation of an active branching sucrase from Lactobacillus kunkeei AP-37 to produce techno-functional poly-oligosaccharides

Glucansucrase AP-37 was extracted from the culture supernatant of Lactobacillus kunkeei AP-37 and characteristics of the glucan produced by the active glucansucrase in terms of structural and functional roles were determined in this study. A molecular weight around 300 kDa was observed for glucansucrase AP-37 and its acceptor reactions with maltose, melibiose and mannose were also conducted to unveil the prebiotic potential of the poly-oligosaccharides formed via these reactions. The core structure of glucan AP-37 was determined by 1H and 13C NMR and GC/MS analysis which revealed that glucan AP-37 was a highly branched dextran composing of high levels of (1 → 3)-linked α-d-glucose units with low levels of (1 → 2)-linked α-d-glucose units. The structural features of the glucan formed, demonstrated that glucansucrase AP-37 was an α-(1 → 3) branching sucrase. Dextran AP-37 was further characterised by FTIR analysis and XRD analysis demonstrated its amorphous nature. A fibrous compact morphology was observed for dextran AP-37 with SEM analysis whereas TGA and DSC analysis revealed its high stability as no degradation was observed up to 312 °C. Finally, the prebiotic potential of the dextran AP-37 and the gluco-oligosaccharides produced with the acceptor reaction of α-(1 → 3) branching sucrase AP-37 were determined and promising results were found for the gluco-oligosaccharides to act as prebiotics.

Facile and efficient chemical synthesis of gluco-oligosaccharides (GlcOS) with diverse glycosidic linkages as potential prebiotics to promote the growth of probiotic bacteria

Glucose-based short-chain oligosaccharides (gluco-oligosaccharides, GlcOS) have been established as functional food ingredients with health-promoting properties. Currently, GlcOS (e.g., isomalto-oligosaccharides, IMOs) are commercially produced via enzymatic processes, which face the challenges of low yield and high cost. Therefore, developing efficient technologies for large-scale production of prebiotic GlcOS is highly desirable. Herein, a facile chemical process was developed to synthesize GlcOS as potential prebiotics via enhanced dehydration condensation of glucose in concentrated sulfuric acid (60-92 %). The maximum GlcOS yield of 83 % was achieved under the optimal condition of 50 % initial glucose loading, 76 % H₂SO₄, 70 °C, and 20 min. Structural analysis revealed that the synthesized GlcOS are mainly short-chain oligomers with a degree of polymerization (DP) between 2 and 4 (46 % DP 2, 22 % DP 3, 12 % DP 4) and a small percentage of larger oligosaccharides (DP 5-9), which are linked by predominantly α- and β-(1→6) linkages along with (1→4), (1→ 3), (1→2), and (1↔1) linkages. In vitro fermentation experiments by probiotic Bifidobacterium bifidum ATCC 29521, Bifidobacterium animalis subsp. lactis DSM 10140, and Limosilactobacillus reuteri ATCC 6475 indicated that the GlcOS can be utilized as a carbon source for bacterial growth, and their promotion effect was overall comparable to three commercial prebiotic IMOs. GlcOS were also successfully synthesized from maltose and cellobiose with similar yield and structures to those from glucose, implying the possibility of synthesizing the prebiotic GlcOS directly from inexpensive starch and cellulose.

Enzymatic Preparation of Gentiooligosaccharides by a Thermophilic and Thermostable β-Glucosidase at a High Substrate Concentration

Gentiooligosaccharides (GnOS) are a kind of oligosaccharide formed by glucose with β-1-6 glycosidic bonds, which has become a new type of functional oligosaccharide for its unique refreshing bitter taste and valuable probiotic effects. However, the research on the enzymatic preparation of GnOS is not thorough enough. In this study, a GH1 thermophilic β-glucosidase from Thermotoga sp. KOL6 was used as a biocatalyst for the synthesis of GnOS. TsBgl1 exhibited excellent thermophilic and thermostable properties by possessing a melting temperature of 101.5 °C and reacting at 80–90 °C efficiently. Its half-life at 90 °C was approximately 5 h, suggesting its high heat resistance as well. TsBgl1 also showed excellent glucose tolerance with an inhibition constant (K_i) of 1720 mM and was stimulated in the presence of 0–900 mM glucose. TsBgl1 showed the highest hydrolytic activity on laminaribiose (Glc-β-1,3-Glc), but mainly synthetized gentiobiose (Glc-β-1,6-Glc) during transglycosylation. By optimizing the reaction conditions and substrate concentration, the highest yield of GnOS synthesized by TsBgl1 reached 144.3 g·L⁻¹ when 1000 g·L⁻¹ glucose was used as a substrate, which was higher than the highest yield ever reported. The thermophilic and thermostable properties of TsBgl1 were considered to be significant advantages in the industrial production of GnOS, where long periods of high-temperature reactions are required. This study was expected to provide an excellent candidate enzyme for industrial production of GnOS and also provide a reference for studying the transglycosylation of GH1 β-glucosidases.

Recent advancements in prebiotic oligomers synthesis via enzymatic hydrolysis of lignocellulosic biomass

Interest in functional food, such as non-digestible prebiotic oligosaccharides is increasing day by day and their production is shifting toward sustainable manufacturing. Due to the presence of high carbohydrate content, lignocellulosic biomass (LCB) is the most-potential, cost-effective and sustainable substrate for production of many useful products, including lignocellulose-derived prebiotic oligosaccharides (LDOs). These have the same worthwhile properties as other common oligosaccharides, such as short chain carbohydrates digestible to the gut flora but not to humans mainly due to their resistance to the low pH and high temperature and their demand is constantly increasing mainly due to increased awareness about their potential health benefits. Despite several advantages over the thermo-chemical route of synthesis, comprehensive and updated information on the conversion of lignocellulosic biomass to prebiotic oligomers via controlled enzymatic saccharification is not available in the literature. Thus, the main objective of this review is to highlight recent advancements in enzymatic synthesis of LDOs, current challenges, and future prospects of sustainably producing prebiotic oligomers via enzymatic hydrolysis of LCB substrates. Enzyme reaction engineering practices, custom-made enzyme preparations, controlled enzymatic hydrolysis, and protein engineering approaches have been discussed with regard to their applications in sustainable synthesis of lignocellulose-derived oligosaccharide prebiotics. An overview of scale-up aspects and market potential of LDOs has also been provided.

Structural and bioactive characteristics of a dextran produced by Lactobacillus kunkeei AK1

In this study, structural and techno-functional characteristics of an exopolysaccharide (EPS) produced by Lactobacillus kunkeei AK1 were determined. High-performance liquid chromatography (HPLC) analysis demonstrated that EPS AK1 was composed of only glucose units. ¹H and ¹³C Nuclear magnetic resonance (NMR) analysis revealed that EPS AK1 was a dextran type EPS containing 4.78% (1 → 4)-linked α-d-glucose branches. The molecular weight of EPS AK1 was determined to be 45 kDa by Gel Permeation Chromatography (GPC) analysis. A high level of thermal stability up to 280 °C was determined for dextran AK1 detected by Differential scanning calorimetry (DSC) and Thermogravimetric analysis (TGA). Dextran AK1 appeared as regular spheres with compact morphology and as irregular particles in the solution with no clear cross-linking between the chains of the polysaccharide observed by Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) analysis, respectively. X-ray diffraction analysis (XRD) analysis demonstrated that dextran AK1 had a crystalline structure. A relatively strong antioxidant activity was observed for dextran AK1 determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging and cupric reducing antioxidant capacity (CUPRAC) tests. Finally, only a digestion ratio of 3.1% was observed for dextran AK1 following the in vitro simulated gastric digestion test.

Production Optimization, Structural Analysis, and Prebiotic- and Anti-Inflammatory Effects of Gluco-Oligosaccharides Produced by Leuconostoc lactis SBC001

Leuconostoc lactis SBC001, isolated from chive, produces glucansucrase and synthesizes oligosaccharides through its enzymatic activity. This study was conducted to optimize oligosaccharide production using response surface methodology, analyze the structure of purified oligosaccharides, and investigate the prebiotic effect on 24 bacterial and yeast strains and the anti-inflammatory activity using RAW 264.7 macrophage cells. The optimal conditions for oligosaccharide production were a culture temperature of 30 °C and sucrose and maltose concentrations of 9.6% and 7.4%, respectively. Based on ¹H-NMR spectroscopic study, the oligosaccharides were identified as gluco-oligosaccharides that consisted of 23.63% α-1,4 glycosidic linkages and 76.37% α-1,6 glycosidic linkages with an average molecular weight of 1137 Da. The oligosaccharides promoted the growth of bacterial and yeast strains, including Lactobacillus plantarum, L. paracasei, L. johnsonii, Leuconostoc mesenteroides, L. rhamnosus, and Saccharomyces cerevisiae. When lipopolysaccharide-stimulated RAW 264.7 cells were treated with the oligosaccharides, the production of nitric oxide was decreased; the expression of inducible nitric oxide synthase, tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and IL-10 was suppressed; and the nuclear factor-kappa B signaling pathway was inhibited. In conclusion, the gluco-oligosaccharides obtained from Leu. lactis SBC001 exhibited a prebiotic effect on six bacterial and yeast strains and anti-inflammatory activity in RAW 264.7 macrophage cells.

In vitro prebiotic potential, digestibility and biocompatibility properties of laminari-oligosaccharides produced from curdlan by β-1,3-endoglucanase from Clostridium thermocellum

Curdlan or laminarin, a β-1,3-glucan was hydrolysed by β-1,3-endoglucanase (CtLam81A) from Clostridium thermocellum to produce laminari-oligosaccharides. TLC analysis of hydrolysed curdlan showed the presence of laminari-oligosaccharides of the degree of polymerization, DP2-DP7. This mixture of laminari-oligosaccharides displayed prebiotic properties. Laminari-oligosaccharides showed an increase in the growth of probiotic bacteria such as Lactobacillus plantarum DM5 and Lactobacillus acidophilus, while they did not promote the growth of non-probiotic bacteria (Escherichia coli and Enterobacter aerogenes). Laminari-oligosaccharides showed higher prebiotic activity score of 0.92 ± 0.01 and 0.64 ± 0.08 for L. plantarum DM5 and L. acidophilus NRRL B-4496, respectively, similar to those shown by inulin. Laminari-oligosaccharides showed higher resistance or low digestibility against α-amylase, artificial gastric juice and intestinal fluid than inulin indicating their bioavailability to the probiotic bacteria present in the gastrointestinal tract of human. The probiotic bacteria consumed laminaribiose and laminariotriose more readily than higher laminari-oligosaccharides as carbon source for their growth. The in vitro cytotoxicity assay of laminari-oligosaccharides (1 mg/ml) on human embryonic kidney (HEK 293) cells showed that the cell viability was not affected even after 72 h indicating their biocompatible nature. All the results amply indicated that laminari-oligosaccharides can serve as potential prebiotic additives for functional food products.

Synthesis of potential prebiotic α-glucooligosaccharides using microbial glucansucrase and their in vitro fecal fermentation

Novel α-glucooligosaccharides were synthesized by the acceptor reaction of Leuconostoc citreum SK24.002 glucansucrase with maltose and sucrose. The impact of synthesis conditions, including the ratio of sucrose to maltose and the substrate concentration, on the formation of α-glucooligosaccharides was evaluated. Under the optimized experimental conditions, the yield of a mixture of α-glucooligosaccharides with DP 3-5 reached approximately 56.4% with a concentration of 170.7 mg mL-1. Each of these α-glucooligosaccharides was purified, and the structures were assigned as follows: α-D-Glcp-(1,6)-α-D-Glcp-(1,4)-D-Glcp (DP3), α-D-Glcp-(1,3)-α-D-Glcp-(1,6)-α-D-Glcp-(1,4)-D-Glcp (DP4), and α-D-Glcp-(1,6)-α-D-Glcp-(1,3)-α-D-Glcp-(1,6)-α-D-Glcp-(1,4)-D-Glcp (DP5), respectively. For these three structurally different oligosaccharides, the fermentation selectivity by fecal bacteria was determined in anaerobic batch culture. Fructooligosaccharide (FOS) was used as a positive prebiotic control. Similar to FOS, all three α-glucooligosaccharides selectively stimulated the proliferation of Bifidobacteria and Lactobacilli compared with the control. DP3 exhibited the strongest prebiotic ability to increase the Bifidobacterium and Lactobacillus population, whereas DP5 produced the most short-chain fatty acids. In addition, DP4 produced the highest butyrate concentration and resulted in the lowest acetate : propionate ratio. These results suggested that the enzymatically synthesized α-glucooligosaccharides were potential prebiotics, underlining correlations between the structural features of oligosaccharides and their impact on the metabolism of fecal microbiota.

Structural Analysis of Gluco-Oligosaccharides Produced by Leuconostoc lactis and Their Prebiotic Effect

Leuconostoc lactis CCK940, which exhibits glycosyltransferase activity, produces oligosaccharides using sucrose and maltose as donor and receptor molecules, respectively. The oligosaccharides produced were purified by Bio-gel P2 chromatography and the purified oligosaccharides (CCK-oligosaccharides) consisted of only glucose. ¹H-NMR analysis revealed that the CCK-oligosaccharides were composed of 77.6% α-1,6 and 22.4% α-1,4 glycosidic linkages, and the molecular weight of the CCK-oligosaccharides was found to be 9.42 × 10² Da. To determine the prebiotic effect of the CCK-oligosaccharides, various carbon sources were added in modified media. Growth of six probiotic strains, Lactobacillus casei, L. pentosus, L. plantarum, Weissella cibaria, Bifidobacterim animalis, and Saccharomyces cerevisiae, was better when the CCK-oligosaccharides were used as the sole carbon source compared to fructo-oligosaccharides, which are widely used as prebiotics. These results showed that the CCK-oligosaccharides produced from Leu. lactis CCK940 could serve as good candidates for novel prebiotics.

Preparation of gentiobiose-derived oligosaccharides by glucansucrase E81 and determination of prebiotic and immune-modulatory functions

Gentiobiose-derived oligosaccharides were synthesized by the acceptor reaction of glucansucrase E81 obtained from Lactobacillus reuteri E81 with sucrose and gentiobiose as donor-acceptor sugars, respectively. The reaction products were monitored by TLC analysis and gentiobiose-derived oligosaccharides up to DP 8 were formed during the acceptor reaction as determined by ESI-MS/MS analysis. The glycosylation of the gentiobiose with α-(1 → 6) linkages and α-(1 → 3) linkages was shown by ¹H and ¹³C NMR analysis confirming the structure of these gentiobiose-derived oligosaccharides. The in vitro prebiotic function of the oligosaccharides was determined in which probiotic strains were stimulated whereas no growth was observed in pathogen strains. Gentiobiose-derived oligosaccharides showed immune-modulatory functions in vitro and triggered the production of IL-4, IL12 and TNF-α cytokines in HT29 cells in a dose dependent manner. This study showed the production and functional characterisation of gentiobiose-derived oligosaccharides establishing a promising avenue for future applications.

Characterization of new oligosaccharide converted from cellobiose by novel strain of Bacillus subtilis

Six bacterial strains isolated from various Korean fermented foods were cultured in cellobiose-containing medium to investigate their potential for producing new kind of oligosaccharides. After bacterial culture in a liquid medium, each culture medium was concentrated and analyzed. TLC analysis revealed that only one strain (Bacillus subtilis SS-76) produced new spot on the TLC plate, indicating that it could converts cellobiose into a new oligosaccharide. Following purification of the culture supernatant of B. subtilis SS-76, the fractions containing the oligosaccharide produced were pooled, and the concentrated fraction was analyzed for its chemical and structural characteristics. By using various analytical techniques such as sugar composition analysis, glycosidic linkage analysis, and molecular weight determination, the new oligosaccharide was identified as glucotriose connected with (1 → 4) and (1 → 3) glycosidic linkages. In addition, the result of specific enzyme catalysis suggested that the new glucotriose might contain only β-configurations in their anomeric configurations.

Prebiotic Oligosaccharides: Special Focus on Fructooligosaccharides, Its Biosynthesis and Bioactivity

The bacterial groups in the gut ecosystem play key role in the maintenance of host's metabolic and structural functionality. The gut microbiota enhances digestion processing, helps in digestion of complex substances, synthesizes beneficial bioactive compounds, enhances bioavailability of minerals, impedes growth of pathogenic microbes, and prevents various diseases. It is, therefore, desirable to have an adequate intake of prebiotic biomolecules, which promote favorable modulation of intestinal microflora. Prebiotics are non-digestible and chemically stable structures that significantly enhance growth and functionality of gut microflora. The non-digestible carbohydrate, mainly oligosaccharides, covers a major part of total available prebiotics as dietary additives. The review describes the types of prebiotic low molecular weight carbohydrates, i.e., oligosaccharides, their structure, biosynthesis, functionality, and applications, with a special focus given to fructooligosaccharides (FOSs). The review provides an update on enzymes executing hydrolytic and fructosyltransferase activities producing prebiotic FOS biomolecules, and future perspectives.

A novel approach of integrated bioprocessing of cane molasses for production of prebiotic and functional bioproducts

In this work, the sugar industry by-product cane molasses was investigated as feedstock for acceptor reactions by dextransucrase from Leuconostoc mesenteroides MTCC 10508, leading to the biosynthesis of oligosaccharides. The starch industry corn fiber residue was used as a source for acceptor molecules, maltose, in the reaction. Production of approximately 124g oligosaccharides (DP3-DP6) per kg of fresh molasses was achieved. Further, cane molasses based medium was demonstrated as a sole carbon source for L. mesenteroides growth and dextransucrase production. d-Fructose released by dextransucrase activity as processing by-product was transformed into the functional monosaccharide with zero caloric value, d-psicose, by inducing its epimerization. Quantitative analysis approximated 37g d-psicose per kg of fresh molasses. Thus, the study established a novel approach of integrated bioprocessing of cane molasses into prebiotic and functional food additives.

Isolation and Structural Characterization of an Oligosaccharide Produced by Bacillus subtilis in a Maltose-Containing Medium

Among 116 bacterial strains isolated from Korean fermented foods, one strain (SS-76) was selected for producing new oligosaccharides in a basal medium containing maltose as the sole source of carbon. Upon morphological characterization using scanning electron microscopy, the cells of strain SS-76 appeared rod-shaped; subsequent 16S rRNA gene sequence analysis revealed that strain SS-76 was phylogenetically close to Bacillus subtilis. The main oligosaccharide fraction B extracted from the culture supernatant of B. subtilis SS-76 was purified by high performance liquid chromatography. Subsequent structural analysis revealed that this oligosaccharide consisted only of glucose, and methylation analysis indicated similar proportions of glucopyranosides in the 6-linkage, 4-linkage, and non-reducing terminal positions. Matrix-assisted laser-induced/ionization time-of-flight/mass spectrometry and electrospray ionization-based liquid chromatography-mass spectrometry/mass spectrometry analyses suggested that this oligosaccharide consisted of a trisaccharide unit with 1,6- and 1,4-glycosidic linkages. The anomeric signals in the (1)H-nuclear magnetic resonance spectrum corresponded to α-anomeric configurations, and the trisaccharide was finally identified as panose (α-D-glucopyranosyl-1,6-α-D-glucopyranosyl-1,4-D-glucose). These results suggest that B. subtilis SS-76 converts maltose into panose; strain SS-76 may thus find industrial application in the production of panose.

Construction of a Recombinant Leuconostoc mesenteroides CJNU 0147 Producing 1,4-Dihydroxy-2-Naphthoic Acid, a Bifidogenic Growth Factor

1,4-Dihydroxy-2-naphthoic acid (DHNA), a precursor of menaquinone (vitamin K2), has an effect on growth stimulation of bifidobacteria and prevention of osteoporosis, making it a promising functional food material. Therefore, we tried to clone the menB gene encoding DHNA synthase from Leuconostoc mesenteroides CJNU 0147. Based on the genome sequence of Leu. mesenteroides ATCC 8293 (GenBank accession no., CP000414), a primer set (Leu_menBfull_F and Leu_menBfull_R) was designed for the PCR amplification of menB gene of CJNU 0147. A DNA fragment (1,190 bp), including the menB gene, was amplified, cloned into pGEM-T Easy vector, and sequenced. The deduced amino acid sequence of MenB (DHNA synthase) protein of CJNU 0147 had a 98% similarity to the corresponding protein of ATCC 8293. The menB gene was subcloned into pCW4, a lactic acid bacteria - E. coli shuttle vector, and transferred to CJNU 0147. The transcription of menB gene of CJNU 0147 (pCW4::menB) was increased, when compared with those of CJNU 0147 (pCW4) and CJNU 0147 (−). The DHNA was produced from it at a detectable level, indicating that the cloned menB gene of CJNU 0147 encoded a DHNA synthase which is responsible for the production of DHNA, resulting in an increase of bifidogenic growth stimulation activity.

Selective Manipulation of the Gut Microbiota Improves Immune Status in Vertebrates

All animals develop in association with complex microbial communities. It is now well established that commensal microbiota is essential for the correct functionality of each organ in the host. Particularly, the commensal gastro-intestinal microbiota (CGIM) is a key factor for development, immunity and nutrient conversion, rendering them bio-available for various uses. Thus, nutritional inputs generate a positive loop in maintaining host health and are essential in shaping the composition of the CGIM communities. Probiotics, which are live exogenous microorganisms, selectively provided to the host, are a promising concept for manipulating the microbiota and thus for increasing the host health status. Nevertheless, most mechanisms induced by probiotics to fortify the immune system are still a matter of debate. Alternatively, prebiotics, which are non-digestible food ingredients, can favor the growth of specific target groups of CGIM. Several metabolites are produced by the CGIM, one of the most important are the short-chain fatty acids (SCFAs), which emerge from the fermentation of complex carbohydrates. SCFAs have been recognized as key players in triggering beneficial effects elicited by simple diffusion and by specific receptors present, thus, far only in epithelial cells of higher vertebrates at different gastro-intestinal locations. However, both strategies have shown to provide resistance against pathogens during periods of high stress. In fish, knowledge about the action of pro- and prebiotics and SCFAs is still limited. Thus, in this review, we briefly summarize the mechanisms described on this topic for higher vertebrates and discuss why many of them may operate in the fish gut representing a model for different mucosal tissues

Draft Genome Sequence of Three Antibiotic-Resistant Leuconostoc mesenteroides Strains of Dairy Origin

Leuconostoc mesenteroides is a lactic acid bacterium (LAB) commonly associated with fermented foods. Here, we report the genome sequence of three selected dairy strains, showing atypical antibiotic resistances (AR). Genome analysis provided a better understanding of the genetic bases of AR in Leuconostoc and its potential transferability among foodborne bacteria.