Determination of the structure of the exopolysaccharide produced by Lactobacillus sake 0-1

Bacterial exopolysaccharides as emerging bioactive macromolecules: from fundamentals to applications

Microbial exopolysaccharides (EPS) are extracellular carbohydrate polymers forming capsules or slimy coating around the cells. EPS can be secreted by various bacterial genera that can help bacterial cells in attachment, environmental adaptation, stress tolerance and are an integral part of microbial biofilms. Several gut commensals (e.g., Lactobacillus, Bifidobacterium) produce EPS that possess diverse bioactivities. Bacterial EPS also has extensive commercial applications in the pharmaceutical and food industries. Owing to the structural and functional diversity, genetic and metabolic engineering strategies are currently employed to increase EPS production. Therefore, the current review provides a comprehensive overview of the fundamentals of bacterial exopolysaccharides, including their classification, source, biosynthetic pathways, and functions in the microbial community. The review also provides an overview of the diverse bioactivities of microbial EPS, including immunomodulatory, anti-diabetic, anti-obesity, and anti-cancer properties. Since several gut microbes are EPS producers and gut microbiota helps maintain a functional gut barrier, emphasis has been given to the intestinal-level bioactivities of the gut microbial EPS. Collectively, the review provides a comprehensive overview of microbial bioactive exopolysaccharides.

Phosphorylated polysaccharides: Applications, natural abundance, and new-to-nature structures generated by chemical and enzymatic functionalization

Polysaccharides are foreseen as serious candidates for the future generation of polymers, as they are biosourced and biodegradable materials. Their functionalisation is an attractive way to modify their properties, thereby increasing their range of applications. Introduction of phosphate groups in polysaccharide chains for the stimulation of the immune system was first described in the nineteen seventies. Since then, the use of phosphorylated polysaccharides has been proposed in various domains, such as healthcare, water treatment, cosmetic, biomaterials, etc. These alternative usages capitalize on newly acquired physico-chemical or biological properties, leading to materials as diverse as flame-resistant agents or drug delivery systems. Phosphorylated polysaccharides are found in Nature and need to be extracted to assess their biological potential. However, they are not abundant, often present complex backbones hard to characterize, and most of them have a low phosphate content. These drawbacks have pushed forward the development of chemical phosphorylation employing a wide variety of phosphorylating agents to obtain polysaccharides with a large range of phosphate content. Chemical phosphorylation requires the use of harsh conditions and toxic, petroleum-based solvents, which hinders their exploitation in the food and health industry. Over the last 20 years, although enzymes are regiospecific catalysts that work in aqueous and mild conditions, enzymatic phosphorylation has been little investigated. To date, only three families of enzymes have been used for the in vitro phosphorylation of polysaccharides. Considering the number of unresolved metabolic pathways leading to phosphorylated polysaccharides, the huge diversity of kinase sequences, and the recent progress in protein engineering one can envision native and engineered kinases as promising tools for polysaccharide phosphorylation.

Carbohydrate esterases involved in deacetylation of food components by the human gut microbiota

Non-carbohydrate modifications such as acetylations are widespread in food stuffs as well as they play important roles in diverse biological processes. These modifications meet the gut environment and are removed from their carbohydrate substrates by the resident microbiota. Among the most abundant modifications are O-acetylations, contributing to polysaccharides physico-chemical properties such as viscosity and gelling ability, as well as reducing accessibility for glycosyl hydrolases, and thus hindering polysaccharide degradation. Of particular note, O-acetylations increase the overall complexity of a polymer, thus requiring a more advanced degrading machinery for microbes to utilize it. This minireview describes acetylesterases from the gut microbiota that deacetylate various food polysaccharides, either as natural components of food, ingredients, stabilizers of microbial origin, or as part of microbes for food and beverage preparations. These enzymes include members belonging to at least 8 families in the CAZy database, as well as a large number of biochemically characterized esterases that have not been classified yet. Despite different structural folds, most of these acetylesterases have a common acid-base mechanism and belong to the SGNH hydrolase superfamily. We highlight examples of acetylesterases that are highly specific to one substrate and to the position of the acetyl group on the glycosyl residue of the carbohydrate, while other members that have more broad substrate specificity. Current research aimed at unveiling the functions and regioselectivity of acetylesterases will help providing fundamental mechanistic understanding on how dietary components are utilized in the human gut and will aid developing applications of these enzymes to manufacture novel industrial products.

Latilactobacillus sakei: a candidate probiotic with a key role in food fermentations and health promotion

Latilactobacillus sakei is used extensively in industrial production and food fermentations. The species is primarily derived from fermented meat and vegetable products and is also found in human feces. Genomics and metabolomics have revealed unique metabolic pathways in L. sakei and molecular mechanisms underlying its competitive advantages in different habitats, which are mostly attributed to its flexible carbohydrate metabolism, cold tolerance, acid and salt tolerance, ability to cope with oxygen changes, and heme uptake. In recent years, probiotic effects of L. sakei and its metabolites have been identified, including the ability to effectively alleviate metabolic syndrome, inflammatory bowel disease, and atopic dermatitis. This review summarizes the genomic and metabolic characteristics of L. sakei and its metabolites and describes their applications, laying a foundation for their expanded use across the food and healthcare industries.

Correlation between exopolysaccharide biosynthesis and gastrointestinal tolerance of Lactiplantibacillus plantarum

AIM

This study aimed to investigate the correlation between the level of exopolysaccharide (EPS) biosynthesis and gastrointestinal tolerance of 12 Lactiplantibacillus plantarum strains.

METHODS AND RESULTS

In this study, the EPS production and survival rate of 12 strains of L. plantarum under gastrointestinal stress were determined. Results showed that the EPS biosynthesis level of L. plantarum in semi-defined medium ranged from 9.84 to 26.05 mg/L. The survival rates of all strains in simulated gastric juice at pH 3.0 ranged from 43.52% to 112.73%. Among them, eight strains were higher than 90%, while only one strain was lower than 50%. The survival rates of all strains in simulated intestinal juice ranged from 50.36% to 125.39%, among which eight strains were higher than 80%. The survival rates of all strains under 0.1% bile salt stress ranged from 3.39% to 109.34%, among which four strains were higher than 80% and three strains were lower than 60%. Besides, the survival rates of all strains under 0.5% bile salt stress ranged from 0.42% to 95.34%. The results indicated that the 12 L. plantarum strains had good tolerance to simulated gastric juice at pH 3.0, simulated intestinal juice and 0.1% bile salt. Notably, it was observed that the survival rates of L. plantarum strains under simulated gastric juice at pH 3.0 and simulated intestinal juice were significantly positively correlated with EPS biosynthesis (p < 0.01).

CONCLUSION

The yield of EPS of L. plantarum was related to simulated gastric juice and simulated intestinal juice environment.

SIGNIFICANCE AND IMPACT OF STUDY

It was speculated that the production of EPS may be one of the strategies for L. plantarum to adapt to the part of gastrointestinal environment. In the future, we could analyse the protection mechanism of EPS from the gene level.

Exopolysaccharide production by lactic acid bacteria: the manipulation of environmental stresses for industrial applications

Exopolysaccharides (EPSs) are biological polymers secreted by microorganisms including Lactic acid bacteria (LAB) to cope with harsh environmental conditions. EPSs are one of the main components involved in the formation of extracellular biofilm matrix to protect microorganisms from adverse factors such as temperature, pH, antibiotics, host immune defenses, etc.. In this review, we discuss EPS biosynthesis; the role of EPSs in LAB stress tolerance; the impact of environmental stresses on EPS production and on the expression of genes involved in EPS synthesis. The evaluation results indicated that environmental stresses can alter EPS biosynthesis in LAB. For further studies, environmental stresses may be used to generate a new EPS type with high biological activity for industrial applications.

EpsA is an essential gene in exopolysaccharide production in Lactobacillus johnsonii FI9785

Lactobacillus johnsonii FI9785 has an eps gene cluster which is required for the biosynthesis of homopolymeric exopolysaccharides (EPS)‐1 and heteropolymeric EPS‐2 as a capsular layer. The first gene of the cluster, epsA, is the putative transcriptional regulator. In this study we showed the crucial role of epsA in EPS biosynthesis by demonstrating that deletion of epsA resulted in complete loss of both EPS‐1 and EPS‐2 on the cell surface. Plasmid complementation of the epsA gene fully restored EPS production, as confirmed by transmission electron microscopy and nuclear magnetic resonance (NMR) analysis. Furthermore, this complementation resulted in a twofold increase in the expression levels of this gene, which almost doubled amounts of EPS production in comparison with the wild‐type strain. Analysis of EPS by NMR showed an increased ratio of the heteropolysaccharide to homopolysaccharide in the complemented strain and allowed identification of the acetylated residue in EPS‐2 as the (1,4)‐linked βGlcp unit, with the acetyl group located at O‐6. These findings indicate that epsA is a positive regulator of EPS production and that EPS production can be manipulated by altering its expression.

Structural investigation of cell wall polysaccharides of Lactobacillus delbrueckii subsp. bulgaricus 17

Lactobacilli are valuable strains for commercial (functional) food fermentations. Their cell surface-associated polysaccharides (sPSs) possess important functional properties, such as acting as receptors for bacteriophages (bacterial viruses), influencing autolytic characteristics and providing protection against antimicrobial peptides. The current report provides an elaborate molecular description of several surface carbohydrates of Lactobacillus delbrueckii subsp. bulgaricus strain 17. The cell surface of this strain was shown to contain short chain poly(glycerophosphate) teichoic acids and at least two different sPSs, designated here as sPS1 and sPS2, whose chemical structures were examined by 2D nuclear magnetic resonance spectroscopy and methylation analysis. Neutral branched sPS1, extracted with n-butanol, was shown to be composed of hexasaccharide repeating units (-[α-d-Glcp-(1-3)-]-4-β-l-Rhap2OAc-4-β-d-Glcp-[α-d-Galp-(1-3)]-4-α-Rhap-3-α-d-Galp-), while the major component of the TCA-extracted sPS2 was demonstrated to be a linear d-galactan with the repeating unit structure being (-[Gro-3P-(1-6)-]-3-β-Galf-3-α-Galp-2-β-Galf-6-β-Galf-3-β-Galp-).

Structure and biosynthesis of two exopolysaccharides produced by Lactobacillus johnsonii FI9785

Exopolysaccharides were isolated and purified from Lactobacillus johnsonii FI9785, which has previously been shown to act as a competitive exclusion agent to control Clostridium perfringens in poultry. Structural analysis by NMR spectroscopy revealed that L. johnsonii FI9785 can produce two types of exopolysaccharide: EPS-1 is a branched dextran with the unusual feature that every backbone residue is substituted with a 2-linked glucose unit, and EPS-2 was shown to have a repeating unit with the following structure: -6)-α-Glcp-(1-3)-β-Glcp-(1-5)-β-Galf-(1-6)-α-Glcp-(1-4)-β-Galp-(1-4)-β-Glcp-(1-. Sites on both polysaccharides were partially occupied by substituent groups: 1-phosphoglycerol and O-acetyl groups in EPS-1 and a single O-acetyl group in EPS-2. Analysis of a deletion mutant (ΔepsE) lacking the putative priming glycosyltransferase gene located within a predicted eps gene cluster revealed that the mutant could produce EPS-1 but not EPS-2, indicating that epsE is essential for the biosynthesis of EPS-2. Atomic force microscopy confirmed the localization of galactose residues on the exterior of wild type cells and their absence in the ΔepsE mutant. EPS2 was found to adopt a random coil structural conformation. Deletion of the entire 14-kb eps cluster resulted in an acapsular mutant phenotype that was not able to produce either EPS-2 or EPS-1. Alterations in the cell surface properties of the EPS-specific mutants were demonstrated by differences in binding of an anti-wild type L. johnsonii antibody. These findings provide insights into the biosynthesis and structures of novel exopolysaccharides produced by L. johnsonii FI9785, which are likely to play an important role in biofilm formation, protection against harsh environment of the gut, and colonization of the host.

Structural characterization of the O-chain polysaccharide of Aeromonas caviae ATCC 15468 lipopolysaccharide

The O-chain polysaccharide produced by a mild acid degradation of Aeromonas caviae ATCC 15468 lipopolysaccharide was found to be composed of L-rhamnose, 2-acetamido-2-deoxy-D-glucose, 2-acetamido-2-deoxy-D-galactose and phosphoglycerol. Subsequent methylation and CE-ESIMS analyses and 1D/2D NMR ((1)H, (13)C and (31)P) spectroscopy showed that the O-chain polysaccharide is a high-molecular-mass acidic branched polymer of tetrasaccharide repeating units with a phosphoglycerol substituent having the following structure: [structure: see text] where Gro represents glycerol and P represents a phosphate group.

Structure of a neutral exopolysaccharide produced by Lactobacillus delbrueckii ssp. bulgaricus LBB.B26

The neutral exopolysaccharide produced by Lactobacillus delbrueckii ssp. bulgaricus LBB.B26 in skimmed milk was found to be composed of d-glucose and d-galactose in a molar ratio of 2:3. Linkage analysis and 1D/2D NMR ((1)H and (13)C) studies performed on the native polysaccharide, and on an oligosaccharide obtained from a partial acid hydrolysate of the native polysaccharide, showed the polysaccharide to consist of branched pentasaccharide repeating units with the following structure. [structure: see text]

Exopolysaccharide expression in Lactococcus lactis subsp. cremoris Ropy352: evidence for novel gene organization

Lactococcus lactis subsp. cremoris Ropy352 produces two distinct heteropolysaccharides, phenotypically described as ropy and mucoid, when cultured in nonfat milk. One exopolysaccharide precipitated with 50% ethanol as a series of elongated threads and was composed of glucose and galactose in a molar ratio of 3:2. The second exopolysaccharide precipitated with 75% ethanol as a fine flocculant and consisted of galactose, glucose, and mannose with a molar ratio of 67:21:12. A mutant strain, L. lactis subsp. cremoris EK240, lacking the ropy phenotype did not produce the exopolysaccharide that precipitated with 50% ethanol; however, it produced the exopolysaccharide that precipitated with 75% ethanol, indicating that the former exopolysaccharide is essential for the ropy phenotype. Cultures of L. lactis subsp. cremoris Ropy352 in 10% nonfat milk reached a viscosity of 25 Pa-s after 24 h, while those of the nonropy L. lactis subsp. cremoris EK240 mutant did not change. A mutation abolishing ropy exopolysaccharide expression mapped to a region on a plasmid containing two open reading frames, epsM and epsN, encoding novel glycosyltransferases bordered by ISS1 elements oriented in the same direction. Sequencing of this plasmid revealed two other regions involved in exopolysaccharide expression, an operon located between partial IS981 and IS982 elements, and an independent gene, epsU. Two and possibly three of these regions are involved in L. lactis subsp. cremoris Ropy352 exopolysaccharide expression and are arranged in a novel fashion different from that of typical lactococcal exopolysaccharide loci, and this provides genetic evidence for exopolysaccharide gene reorganization and evolution in Lactococcus.

Isolation and characterization of two exopolysaccharides produced by Lactobacillus plantarum EP56

A Lactobacillus plantarum strain producing exopolysaccharides (EPSs) was isolated from corn silage. When this strain, named L. plantarum EP56, was grown on a chemically defined medium, two EPS fractions were isolated. The cell-bound EPS fraction (EPS-b) was composed of a single high-molecular-mass polymer of 8.5x10(5) Da containing glucose, galactose and N-acetylgalactosamine in a molar ratio of approximately 3:1:1 and traces of glycerol and phosphoglycerol. The released EPS fraction (EPS-r) was composed of the high-molecular-mass bound polysaccharide and a second polymer of 4x10(4) Da containing glucose, galactose and rhamnose in a molar ratio of 3:1:1 and traces of glycerol and phosphoglycerol. EPS-b and EPS-r contained phosphate which contributes to their negative net charge. Studies on polysaccharide production and location showed that both polymers were synthesized during the exponential growth phase and that the EPS-b polymer was progressively released into the culture medium during the stationary growth phase. Carbon source and temperature influenced EPS synthesis when L. plantarum EP56 was grown in a chemically defined medium. Lactose was the most efficient carbon source among the five tested (glucose, galactose, fructose, lactose and sucrose). EPS production was also increased when the incubation temperature is lowered.

Molecular organization of exopolysaccharide (EPS) encoding genes on the lactococcal bacteriophage adsorption blocking plasmid, pCI658

The lactococcal plasmid pCI658 (58 kb) isolated from Lactococcus lactis ssp. cremoris HO2 encodes the production of a hydrophilic exopolysaccharide (EPS) which consists primarily of galactose and glucuronic acid and which interferes with adsorption of phages ø712 and øc2 to cell surface receptors. Examination of the nucleotide sequence of a 21.8-kb region of the plasmid revealed a large genetic cluster consisting of at least 23 putative EPS biosynthetic determinants in addition to the presence of insertion sequences at the 5(') and 3(') ends. According to homology searches, the genes were organized in specific regions involved in regulation, synthesis and export of the EPS. The predicted products of individual genes exhibited significant homology to exopolysaccharide, capsular polysaccharide (CPS), and lipopolysaccharide (LPS) gene products from a variety of Gram positive and Gram negative bacteria. Evidence of a gene encoding UDP-glucose dehydrogenase is also presented and this is the first description of such a gene in Lactococcus.

UDP-N-acetylglucosamine 4-epimerase activity indicates the presence of N-acetylgalactosamine in exopolysaccharides of Streptococcus thermophilus strains

The monomer composition of the exopolysaccharides (EPS) produced by Streptococcus thermophilus LY03 and S. thermophilus Sfi20 were evaluated by high-pressure liquid chromatography with amperometric detection and nuclear magnetic resonance spectroscopy. Both strains produced the same EPS composed of galactose, glucose, and N-acetylgalactosamine. Further, it was demonstrated that the activity of the precursor-producing enzyme UDP-N-acetylglucosamine 4-epimerase, converting UDP-N-acetylglucosamine into UDP-N-acetylgalactosamine, is responsible for the presence of N-acetylgalactosamine in the EPS repeating units of both strains. The activity of UDP-N-acetylglucosamine 4-epimerase was higher in both S. thermophilus strains than in a non-EPS-producing control strain. However, the level of this activity was not correlated with EPS yields, a result independent of the carbohydrate source applied in the fermentation process. On the other hand, both the amounts of EPS and the carbohydrate consumption rates were influenced by the type of carbohydrate source used during S. thermophilus Sfi20 fermentations. A correlation between activities of the enzymes alpha-phosphoglucomutase, UDP-glucose pyrophosphorylase, and UDP-galactose 4-epimerase and EPS yields was seen. These experiments confirm earlier observed results for S. thermophilus LY03, although S. thermophilus Sfi20 preferentially consumed glucose for EPS production instead of lactose in contrast to the former strain.

Exopolysaccharide (EPS) biosynthesis by Lactobacillus sakei 0-1: production kinetics, enzyme activities and EPS yields

AIMS

To determine optimal exopolysaccharide (EPS) production conditions of the mesophilic lactic acid bacterium strain Lactobacillus sakei 0-1 and to detect possible links between EPS yields and the activity of relevant enzymes.

METHODS AND RESULTS

Fermentation experiments at different temperatures using either glucose or lactose were carried out. EPS production took place during the exponential growth phase. Low temperatures, applying glucose as carbohydrate source, resulted in the best bacterial growth, the highest amounts of EPS and the highest specific EPS production. Activities of 10 important enzymes involved in the EPS biosynthesis and the energy formation of Lact. sakei 0-1 were measured. The obtained results revealed that there is a clear link for some enzymes with EPS biosynthesis. It was also demonstrated clearly that the presence of rhamnose in the EPS building blocks is due to high activities of the enzymes involved in the rhamnose synthetic branch.

CONCLUSION

EPS production in Lact. sakei 0-1 is growth-associated and displays primary metabolite kinetics. Glucose as carbohydrate source and low temperatures enhance the EPS production. The enzymes involved in the biosynthesis of the activated sugar nucleotides play a major role in determining the monomeric composition of the synthesized EPS.

SIGNIFICANCE AND IMPACT OF THE STUDY

The proposed results contribute to a better understanding of the physiological factors influencing EPS production and the key enzymes involved in EPS biosynthesis by Lact. sakei.

Structural characterisation of the exopolysaccharide produced by Streptococcus thermophilus EU20

Streptococcus thermophilus EU20 when grown on skimmed milk secretes a high-molecular-weight exopolysaccharide that is composed of glucose, galactose and rhamnose in a molar ratio of 2:3:2. Using chemical techniques and 1D and 2D-NMR spectroscopy (1H and 13C) the polysaccharide has been shown to possess a heptasaccharide repeating unit having the following structure: [chemical structure: see text]. Treatment of the polysaccharide with mild acid (0.5 M TFA, 100 degrees C for 1 h) liberates two oligosaccharides; the components correspond to the repeating unit and a hexasaccharide equivalent to the repeating unit minus the terminal alpha-L-Rhap.

Structure of the exopolysaccharide produced by Streptococcus thermophilus S3

The exopolysaccharide of Streptococcus thermophilus S3, produced in skimmed milk, is composed of D-galactose and L-rhamnose in a molar ratio of 2:1. The polysaccharide contains 0.4 equiv of O-acetyl groups per repeating unit. Linkage analysis and 1D/2D NMR (1H and 13C) studies on native and O-deacetylated EPS together with nanoES-CID tandem mass spectrometry studies on oligosaccharides generated by a periodate oxidation protocol, show the polysaccharide to have the following structure: [structure: see text].

Structure of the extracellular polysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus 291

The lactic acid bacterium Lactobacillus delbrueckii subsp. bulgaricus 291, when grown in skimmed milk, produced 80 mg/L exopolysaccharide with an average molecular mass of 1.4 x 10(3) kDa. Monosaccharide analysis, methylation analysis, MS, and 1D/2D NMR (1H and 13C) studies performed on the native polysaccharide, and on oligosaccharides obtained from a mild acid hydrolysate of the native polysaccharide, showed the polysaccharide to consist of branched pentasaccharide repeating units with the following structure: [structure: see text].

Structure and properties of the exopolysaccharide produced by Streptococcus macedonicus Sc136

Streptococcus macedonicus is a Gram positive lactic acid bacterium that is part of the starter flora present in Greek sheep and goat cheeses. The S. macedonicus Sc136 strain produces a high-molecular-mass, highly texturizing exopolysaccharide composed of D-glucose, D-galactose, and N-acetyl-D-glucosamine in the molar ratio of 3:2:1. The structure of the exopolysaccharide produced by S. macedonicus Sc136 was determined by chemical analysis, mass spectrometry, and nuclear magnetic resonance spectroscopy. The repeating unit was shown to be: (see text) The polysaccharide sidechain beta-D-Galf-(1-->6)-beta-D-Glcp-(1-->6)-beta-D-GlcpNAc is a key factor in the highly texturizing properties of the S.macedonicus Sc136 exopolysaccharide. Finally, the trisaccharide sequence beta-D-GlcpNAc-(1-->3)-beta-D-Galp-(1-->4)-beta-D-Glcp corresponds to the internal backbone of the lacto-N-tetraose and lacto-N-neotetraose units, which serve as a structural basis for the large majority of human milk oligosaccharides, an additional property offering an important potential for the development of improved infant nutrition products.

Structure of a viscous exopolysaccharide produced by Lactobacillus helveticus K16

A viscous extracellular polysaccharide produced by Lactobacillus helveticus K16 has been investigated. Sugar and methylation analysis, 1H and 13C NMR spectroscopy revealed that the polysaccharide is composed of a hexasaccharide repeating unit. The sequence of sugar residues was determined by use of two-dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple bond connectivity experiments. The structure of the repeating unit of the exopolysaccharide from L. helveticus K16 is as follows: carbohydrate sequence [see text].

Purification and characterisation of a beta-galactosidase from Aspergillus aculeatus with activity towards (modified) exopolysaccharides from Lactococcus lactis subsp. cremoris B39 and B891

Beta-galactosidase from Aspergillus aculeatus was purified from a commercial source for its hydrolytic activity towards (modified) exopolysaccharides (EPSs) produced by Lactococcus lactis subsp. cremoris B39 and B891. The enzyme had a molecular mass of approximately 120 kDa, a pI between 5.3 and 5.7 and was optimally active at pH 5.4 and 55-60 degrees C. Based on the N-terminal amino acid sequence, the enzyme probably belongs to family 35 of the glycosyl hydrolases. The catalytic mechanism was shown to be retaining and transglycosylation products were demonstrated using lactose as a substrate. The beta-galactosidase was also characterised using its activity towards two EPSs having lactosyl side chains attached to different backbone structures. The enzyme degraded O-deacetylated EPS B891 faster than EPS B39. Furthermore, the presence of acetyl groups in EPS B891 slowed down the hydrolysing rate, but the enzyme was still able to release all terminally linked galactose.

Structural characterisation and enzymic modification of the exopolysaccharide produced by Lactococcus lactis subsp. cremoris B891

Lactococcus lactis subsp. cremoris B891 grown on whey permeate produced an exopolysaccharide containing D-Gal and D-Glc in a molar ratio of 2:3. The polysaccharide was partially O-acetylated. By means of HF solvolysis, O-deacetylation, enzymic modification, sugar linkage analysis and ID/2D NMR studies the exopolysaccharide was shown to be composed of repeating units with the following structure: [structure: see text].

Solution properties of viilian, the exopolysaccharide from Lactococcus lactis subsp. cremoris SBT 0495

The exopolysaccharide (EPS) "viilian" was isolated from a large-batch fermentation of Lactococcus lactis subsp. cremoris SBT 0495. After applying a newly developed purification procedure, pure viilian with a weight-averaged molar mass of 2.64 x 10(3) kg/mol was obtained in a yield of 0.6 g/L culture broth. The native EPS, as well as lower molar mass fractions obtained by sonication of the native polymer, were studied by capillary viscometry and size-exclusion chromatography (SEC) coupled to multiangle laser light scattering detection (MALLS). From the viscosity data at various ionic strengths, we extracted a Mark-Houwink-Kuhn-Sakurada exponent a = 0.79, and a Smidsrod B value of 0.03. By application of the Hearst, Bohdanecký, and Odijk models for stiff polymer coils, in connection to the experimental viscosity data, we established the characteristic ratio to be C(infinity) = 44 and the intrinsic persistence length q(0) = 11.5 nm. The rms radii of gyration predicted from each of the models were in good agreement with the experimental radii (e.g., <S(2)>(1/2)(w) = 162 nm for native viilian in 0.2M NaNO(3)), as determined by SEC-MALLS. In addition, the Odijk model predicts correct ionic strength-linear charge density dependence of the rms radius of gyration. From the combined viscosity and SEC-MALLS experiments we concluded that, in dilute aqueous solutions, viilian behaves as an intermediately stiff, random coil polyelectrolyte system.

Structural elucidation of the viscous exopolysaccharide produced by Lactobacillus helveticus Lb161

A viscous extracellular polysaccharide produced by Lactobacillus helveticus Lb161 isolated from raw milk has been investigated. Sugar and methylation analysis, and 1H and 13C NMR spectroscopy revealed that the polysaccharide is composed of a heptasaccharide repeating unit. The sequence of sugar residues was determined by use of two-dimensional nuclear Overhauser effect spectroscopy and heteronuclear multiple bond connectivity experiments. The structure of the repeating unit of the exopolysaccharide from L. helveticus Lb161 is as follows: carbohydrate structure [see text]. The polysaccharide contains approximately 0.6 equivalents of O-acetyl group per repeating unit (not located).

Structural characterisation and enzymic modification of the exopolysaccharide produced by Lactococcus lactis subsp. cremoris B39

Lactococcus lactis subsp. cremoris B39 grown on whey permeate produced an exopolysaccharide containing L-Rha, D-Gal and D-Glc in a molar ratio of 2:3:2. The polysaccharide was modified using an enzyme preparation from Aspergillus aculeatus, resulting in the release of Gal and a polymer with approximately the same hydrodynamic volume as the native polysaccharide. Linkage analysis and 1H NMR studies of both the native and modified exopolysaccharides elucidated that terminally linked Gal was released during modification and that the chemical structure of the branches within the repeating units is: beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->. 2D NMR experiments (both 1H-1H and 1H-13C) revealed that exopolysaccharide B39 consists of a branched heptasaccharide repeating unit with the following structure: [structure: see text].

Unraveling the function of glycosyltransferases in Streptococcus thermophilus Sfi6

Streptococcus thermophilus Sfi6 produces a texturizing exopolysaccharide (EPS) consisting of a -->3)[alpha-D-Galp-(1-->6)]-beta-D-Glcp-(1-->3)-alpha-D-GalpNAc-(1--> 3)-beta-D-Galp-(1--> repeating unit. We previously identified and analyzed a 14.5-kb gene cluster from S. thermophilus Sfi6 consisting of 13 genes responsible for its EPS production. Within this gene cluster, we found a central region of genes (epsE, epsF, epsG, and epsI) that showed similarity to glycosyltransferases. In this study, we investigated the sugar specificity of these enzymes. EpsE catalyzes the first step in the biosynthesis of the EPS repeating unit. It exhibits phosphogalactosyltransferase activity and transfers galactose onto the lipophilic carrier. The second step is fulfilled by EpsG, which transfers an alpha-N-acetylgalactosamine onto the first beta-galactoside. The activity of EpsF was determined by characterizing the EPS produced by an S. thermophilus epsF deletion mutant. This EPS consisted of the monosaccharides Gal, Glc, and GalNAc in an approximately equimolar ratio, thus suggesting that epsF codes for the branching galactosyltransferase. epsI probably codes for the beta-1,3-glucosyltransferase, since it is the only glycosyltransferase to which no gene has been assigned and it exhibits similarity to other beta-glycosyltransferases. EpsE shows the conserved features of phosphoglycosyltransferases, whereas EpsF and EpsG exhibit the primary structure of alpha-glycosyltransferases, belonging to glycosyltransferase family 4, whose members are conserved in all major phylogenetic lineages, including the Archaea and Eukaryota.

Indication that the nitrogen source influences both amount and size of exopolysaccharides produced by streptococcus thermophilus LY03 and modelling of the bacterial growth and exopolysaccharide production in a complex medium

Streptococcus thermophilus LY03 is a yogurt strain producing the same exopolysaccharide material in both milk and MRS broth. Actually, two types of exopolysaccharides are produced simultaneously. The two exopolysaccharides are identical in monomer composition (galactose and glucose in a 4:1 ratio) but differ in molecular size. Gel permeation chromatography revealed a high-molecular-mass exopolysaccharide (1.8 x 10(6)) and a low-molecular-mass exopolysaccharide (4.1 x 10(5)). Both exopolysaccharides can be isolated from the fermentation broth separately. The proportion in which they are produced is strongly dependent on the carbon/nitrogen ratio of the fermentation broth. A shift from a high-molecular-mass exopolysaccharide to a low-molecular-mass exopolysaccharide was observed with increasing initial complex nitrogen concentrations. All necessary biokinetic parameters to study the kinetics of S. thermophilus LY03 fermentations were obtained from a mathematical model which describes both S. thermophilus LY03 growth and exopolysaccharide production and degradation. The model is valid with various initial complex nitrogen concentrations and can be applied to simulate exopolysaccharide production in a milk medium.

Depletion interaction of casein micelles and an exocellular polysaccharide

Casein micelles become mutually attractive when an exocellular polysaccharide produced by Lactococcus lactis subsp. cremoris NIZO B40 (hereafter called EPS) is added to skim milk. The attraction can be explained as a depletion interaction between the casein micelles induced by the nonadsorbing EPS. We used three scattering techniques (small-angle neutron scattering, turbidity measurements, and dynamic light scattering) to measure the attraction. In order to connect the theory of depletion interaction with experiment, we calculated structure factors of hard spheres interacting by a depletion pair potential. Theoretical predictions and all the experiments showed that casein micelles became more attractive upon increasing the EPS concentration.

Introduction of the exopolysaccharide gene cluster from Streptococcus thermophilus Sfi6 into Lactococcus lactis MG1363: production and characterization of an altered polysaccharide

Streptococcus thermophilus Sfi6 produces an exopolysaccharide (EPS) composed of glucose, galactose and N-acetylgalactosamine in the molar ratio of 1:2:1. The genes responsible for the EPS biosynthesis have been isolated previously and found to be clustered in a 14.5 kb region encoding 13 genes. Transfer of this gene cluster into a non-EPS-producing heterologous host, Lactococcus lactis MG1363, yielded an EPS with a similar high molecular weight, but a different structure from the EPS from the native host. The structure of the recombinant EPS was determined by means of 1H homonuclear and 1H-13C heteronuclear two-dimensional nuclear magnetic resonance (NMR) spectra and was found to be --> 3)-beta-D-Glcp-(1 --> 3)-alpha-D-Galp-(1 --> 3)-beta-D-Galp-(1 --> as opposed to --> 3)[alpha-D-Galp-(1 --> 6)]-beta-D-Glcp-(1 --> 3)-alpha-D-GalpNAc-(1 --> 3)-beta-D-Galp-(1 --> for the wild-type S. thermophilus Sfi6. Furthermore, L. lactis MG1363 (pFS101) was also lacking a UDP-N-acetylglucosamine C4-epimerase activity, which would provide UDP-GalNAc for a GalNAc incorporation into the EPS and probably caused the substitution of GalNAc by Gal in the recombinant EPS. This modification implies that (i) bacterial glycosyltransferases could potentially have multiple specificities for the donor and the acceptor sugar molecule; and (ii) the repeating unit polymerase can recognize and polymerize a repeating unit that differs in the backbone as well as in the side-chain from its native substrate.

Isolation and physical characterization of an exocellular polysaccharide

The physical properties of a polysaccharide produced by the lactic acid bacterium Lactococcus lactis subsp. cremoris strain NIZO B40 were investigated. Separation of the polysaccharide from most low molar mass compounds in the culture broth was performed by filtration processes. Residual proteins and peptides were removed by washing with a mixture of formic acid, ethanol, and water. Gel permeation chromatography (GPC) was used to size fractionate the polysaccharide. Fractions were analyzed by multiangle static light scattering in aqueous 0.10 M NaNO3 solutions from which a number- (Mn) and weight-averaged (Mw) molar mass of (1.47 +/- 0.06).10(3) and (1.62 +/- 0.07).10(3) kg/mol, respectively, were calculated so that Mw/Mn approximately 1.13. The number-averaged radius of gyration was found to be 86 +/- 2 nm. From dynamic light scattering an apparent z-averaged diffusion coefficient was obtained. Upon correcting for the contributions from intramolecular modes by extrapolating to zero wave vector a hydrodynamic radius of 86 +/- 4 nm was calculated. Theoretical models for random coil polymers show that this z-averaged hydrodynamic radius is consistent with the z-averaged radius of gyration, 97 +/- 3 nm, as found with GPC.