Efficient synthesis and characterization of lactulosucrose by Leuconostoc mesenteroides B-512F dextransucrase

Nisin controlled homologous Over-expression of an exopolysaccharide biosynthetic glycosyltransferase gene for enhanced EPS production in Lactobacillus plantarum BR2

Glycosyltransferases synthesize a variety of exopolysaccharides (EPS) with different properties by altering the type of glycosidic linkage, degree of branching, length, mass, and conformation of the polymers. The genome analysis of an EPS-producing, Lactobacillus plantarum BR2 (Accession No: MN176402) showed twelve glycosyltransferase genes, and the gene BR2gtf (1116 bp), annotated as an EPS biosynthetic glycosyltransferase was cloned into the pNZ8148 vector. The recombinant pNZ8148 vector along with pNZ9530, a regulatory plasmid, were electroporated to L. plantarum BR2 for the over-expression of gtf gene under a nisin-controlled expression system and the glycosyltransferase activity of the recombinant and the wild-type strains were analysed. The recombinant strain showed 54.4% increase in EPS production with the maximum EPS production of 23.2 ± 0.5 g/L in a 5 L bioreactor study after 72 h of fermentation. This study shows an effective molecular strategy possibly to be adopted in lactic acid bacteria to enhance exopolysaccharide production.

The bifidogenic effects and dental plaque deformation of non-digestible isomaltooligosaccharides synthesized by dextransucrase and alternansucrase

Non-digestible isomaltooligosaccharides (NDIMOS) are functional food and beverage ingredients that contributed to human health benefits through metabolism of gastrointestinal microorganism. In this study, NDIMOS were synthesized by combine dextransucrase from Leuconostoc mesenteroides B512F/KM and alternansucrase from L. mesenteroides NRRL 1355CF10/KM using sucrose as substrate and maltose as acceptor. Their digestibility was confirmed by using digestive enzymes including α-amylase and amyloglucosidase. NDIMOS inhibited insoluble glucan formation through mutansucrase from Streptococcus mutans. The bifidogenic effect of NDIMOS was investigated by growth of four strains of Bifidobacterium in MRS broth containing NDIMOS, compared with MRS broth contain glucose and negative control. Additionally, Bifidobacterium bifidum or Bifidobacterium adolescentis inhibited the growth of Salmonella enterica serovar typhimurium when they were co-cultivation in MRS broth containing NDIMOS. These results suggested that NDIMOS is potential functional ingredient for food, beverage, and pharmaceutical application.

Reuteransucrase-catalytic kinetic modeling and functional characteristics for novel prebiotic gluco-oligomers

This work describes the reuteransucrase-catalyzed reaction and structural characterization as well as in vitro fermentation for the acceptor products of gluco-oligomers from sucrose and maltose. At a low concentration of sucrose, the production of gluco-oligomers was favored, resulting in a relatively large number of acceptor products (DP3-5). A mathematical model was also proposed to simulate gluco-oligomer production depending on the reaction conditions. The fine structures of major linear gluco-oligomer fractions for a sucrose : maltose ratio of 1 : 1 were assigned as follows: α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-d-Glcp, α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-d-Glcp, α-d-Glcp-(1→4)-α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-d-Glcp, and α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-d-Glcp, respectively. Compared with dextran and GOS57, the results of fermentation selectivity indicated that gluco-oligomers promoted the proliferation of gut bacteria and total SCFA production with a higher concentration of propionate. These data suggested that the gluco-oligomers synthesized via the reuteransucrase acceptor reaction had a prebiotic effect on gastrointestinal health.

Metabolism of biosynthetic oligosaccharides by human-derived Bifidobacterium breve UCC2003 and Bifidobacterium longum NCIMB 8809

This work aimed to investigate the ability of two human-derived bifidobacterial strains, i.e. Bifidobacterium breve UCC2003 and Bifidobacterium longum NCIMB 8809, to utilize various oligosaccharides (i.e., 4-galactosyl-kojibiose, lactulosucrose, lactosyl-oligofructosides, raffinosyl-oligofructosides and lactulose-derived galacto-oligosaccharides) synthesized by means of microbial glycoside hydrolases. With the exception of raffinosyl-oligofructosides, these biosynthetic oligosaccharides were shown to support growth acting as a sole carbon and energy source of at least one of the two studied strains. Production of short-chain fatty acids (SCFAs) as detected by HPLC analysis corroborated the suitability of most of the studied novel oligosaccharides as fermentable growth substrates for the two bifidobacterial strains, showing that acetic acid is the main metabolic end product followed by lactic and formic acids. Transcriptomic and functional genomic approaches carried out for B. breve UCC2003 allowed the identification of key genes encoding glycoside hydrolases and carbohydrate transport systems involved in the metabolism of 4-galactosyl-kojibiose and lactulosucrose. In particular, the role of β-galactosidases in the hydrolysis of these particular trisaccharides was demonstrated, highlighting their importance in oligosaccharide metabolism by human bifidobacterial strains.

Enzymatic Synthesis and Structural Characterization of Theanderose through Transfructosylation Reaction Catalyzed by Levansucrase from Bacillus subtilis CECT 39

This work addresses the high-yield and fast enzymatic production of theanderose, a naturally occurring carbohydrate, also known as isomaltosucrose, whose chemical structure determined by NMR is α-d-glucopyranosyl-(1 → 6)-α-d-glucopyranosyl-(1 → 2)-β-d-fructofuranose. The ability of isomaltose to act as an acceptor in the Bacillus subtilis CECT 39 levansucrase-catalyzed transfructosylation reaction to efficiently produce theanderose in the presence of sucrose as a donor is described by using four different sucrose:isomaltose concentration ratios. The maximum theanderose concentration ranged from 122.4 to 130.4 g L^-1, was obtained after only 1 h and at a moderate temperature (37 °C), leading to high productivity (109.7-130.4 g L^-1h^-1) and yield (up to 37.3%) values. The enzymatic synthesis was highly regiospecific, since no other detectable acceptor reaction products were formed. The development of efficient and cost-effective procedures for the biosynthesis of unexplored but appealing oligosaccharides as potential sweeteners, such as theanderose, could help to expand its potential applications which are currently limited by their low availability.

Characterization of the glucansucrase GTF180 W1065 mutant enzymes producing polysaccharides and oligosaccharides with altered linkage composition

Exopolysaccharides produced by lactic acid bacteria are extensively used for food applications. Glucansucrase enzymes of lactic acid bacteria use sucrose to catalyze the synthesis of α-glucans with different linkage compositions, size and physico-chemical properties. Crystallographic studies of GTF180-ΔN show that at the acceptor binding sites +1 and +2, residue W1065 provides stacking interactions to the glucosyl moiety. However, the detailed functional roles of W1065 have not been elucidated. We performed random mutagenesis targeting residue W1065 of GTF180-ΔN, resulting in the generation of 10 mutant enzymes that were characterized regarding activity and product specificity. Characterization of mutant enzymes showed that residue W1065 is critical for the activity of GTF180-ΔN. Using sucrose, and sucrose (donor) plus maltose (acceptor) as substrates, the mutant enzymes synthesized polysaccharides and oligosaccharides with changed linkage composition. The stacking interaction of an aromatic residue at position 1065 is essential for polysaccharide synthesis.

Exploring the transferase activity of Ffase from Schwanniomyces occidentalis, a β-fructofuranosidase showing high fructosyl-acceptor promiscuity

The β-fructofuranosidase from the yeast Schwanniomyces occidentalis (Ffase) produces the prebiotic sugars 6-kestose and 1-kestose by transfructosylation of sucrose, which makes it of biotechnological interest. In this study, the hydrolase and transferase activity of this enzyme was kinetically characterized and its potential to synthesize new fructosylated products explored. A total of 40 hydroxylated compounds were used as potential fructosyl-acceptor alternatives to sucrose. Only 17 of them, including some monosaccharides, disaccharides, and oligosaccharides as well as alditols and glycosides were fructosylated. The best alternative acceptors were the alditols. The major transfer product of the reaction including mannitol was purified and characterized as 1-O-β-D-fructofuranosyl-D-mannitol, whose maximum concentration reached 44 g/L, representing about 7.3 % of total compounds in the mixture and 89 % of all products generated by transfructosylation. The reactions including erythritol produced 35 g/L of an isomer mixture comprising 1- and 4-O-β-D-fructofuranosyl-D-erythritol. In addition, Ffase produced 24 g/L of the disaccharide blastose by direct fructosylation of glucose, which makes it the first enzyme characterized from yeast showing this ability. Thus, novel fructosylated compounds with potential applications in food and pharmaceutical industries can be obtained due to the Ffase fructosyl-acceptor promiscuity.

Truncation of domain V of the multidomain glucansucrase GTF180 of Lactobacillus reuteri 180 heavily impairs its polysaccharide-synthesizing ability

Glucansucrases are exclusively found in lactic acid bacteria and synthesize a variety of α-glucans from sucrose. They are large multidomain enzymes belonging to the CAZy family 70 of glycoside hydrolase enzymes (GH70). The crystal structure of the N-terminal truncated GTF180 of Lactobacillus reuteri 180 (GTF180-ΔN) revealed that the polypeptide chain follows a U shape course to form five domains, including domains A, B, and C, which resemble those of family GH13 enzymes, and two extra and novel domains (domains IV and V), which are attached to the catalytic core. To elucidate the functional roles of domain V, we have deleted the domain V fragments from both the N- and C-terminal ends (GTF180-ΔNΔV). Truncation of domain V of GTF180-ΔN yielded a catalytically fully active enzyme but with heavily impaired polysaccharide synthesis ability. Instead, GTF180-ΔNΔV produced a large amount of oligosaccharides. Domain V is not involved in determining the linkage specificity, and the size of polysaccharide produced as the polysaccharide produced by GTF180-ΔNΔV was identical in size and structure with that of GTF180-ΔN. The data indicates that GTF180-ΔNΔV acts nonprocessively, frequently initiating synthesis of a new oligosaccharide from sucrose, instead of continuing the synthesis of a full size polysaccharide. Mutations L940E and L940F in GTF180-ΔNΔV, which are involved in the acceptor substrate binding, restored polysaccharide synthesis almost to the level of GTF180-ΔN. These results demonstrated that interactions of growing glucan chains with both domain V and acceptor substrate binding sites are important for polysaccharide synthesis.

Synthesis and characterization of isomaltulose-derived oligosaccharides produced by transglucosylation reaction of Leuconostoc mesenteroides dextransucrase

This paper reports the efficient enzymatic synthesis of a homologous series of isomaltulose-derived oligosaccharides with degrees of polymerization ranging from 3 to 9 through the transglucosylation reaction using a dextransucrase from Leuconostoc mesenteroides B-512F. The total oligosaccharide yield obtained under optimal conditions was 41-42% (in weight with respect to the initial amount of isomaltulose) after 24-48 h of reaction. Nuclear magnetic resonance (NMR) structural characterization indicated that dextransucrase specifically transferred glucose moieties of sucrose to the C-6 of the nonreducing glucose residue of isomaltulose. Likewise, monitoring the progression of the content of each individual oligosaccharide indicated that oligosaccharide acceptor products of low molecular weight acted in turn as acceptors for further transglucosylation to yield oligosaccharides of a higher degree of polymerization. The produced isomaltulose-derived oligosaccharides can be considered as isomalto-oligosaccharides (IMOs) because they are linked by only α-(1→6) bonds. In addition, having isomaltulose as the core structure, these IMO-like structures could possess appealing bioactive properties that could find potential applications as functional food ingredients.

Synthesis of novel bioactive lactose-derived oligosaccharides by microbial glycoside hydrolases

Prebiotic oligosaccharides are increasingly demanded within the Food Science domain because of the interesting healthy properties that these compounds may induce to the organism, thanks to their beneficial intestinal microbiota growth promotion ability. In this regard, the development of new efficient, convenient and affordable methods to obtain this class of compounds might expand even further their use as functional ingredients. This review presents an overview on the most recent interesting approaches to synthesize lactose-derived oligosaccharides with potential prebiotic activity paying special focus on the microbial glycoside hydrolases that can be effectively employed to obtain these prebiotic compounds. The most notable advantages of using lactose-derived carbohydrates such as lactosucrose, galactooligosaccharides from lactulose, lactulosucrose and 2-α-glucosyl-lactose are also described and commented.

Analysis, structural characterization, and bioactivity of oligosaccharides derived from lactose

The increasing interest for prebiotic carbohydrates as functional food ingredients has promoted the synthesis of galactooligosaccharides and new lactose derivatives. This review provides a comprehensive overview on the chromatographic analysis, structural characterization, and bioactivity studies of lactose-derived oligosaccharides. The most common chromatographic techniques used for the separation and structural characterization of this type of oligosaccharides, including GC and HPLC in different operational modes, coupled to various detectors are discussed. Insights on oligosaccharide MS fragmentation patterns, using different ionization sources and mass analyzers, as well as data on structural analysis by NMR spectroscopy are also described. Finally, this article deals with the bioactive effects of galacto oligosaccharides and oligosaccharides derived from lactulose on the gastrointestinal and immune systems, which support their consumption to provide significant health benefits.