Structure of an extracellular polysaccharide produced by Lactobacillus rhamnosus strain C83

Preparation, partial characterization and biological activity of exopolysaccharides produced from Lactobacillus fermentum S1

A high slime-producing Lactobacillus fermentum strain (named as L. fermentum S1) was isolated from traditional fermented Fuyuan pickle, which was made of white turnip and collected from Fuyuan county, Yunnan province, China. We extracted and purified the exopolysaccharides from L. fermentum S1, and investigated their preliminary structure characteristics and biological activities. Three purified exopolysaccharide fractions, designated as EPS1, EPS2 and EPS3, were obtained from the culture supernatant of L. fermentum S1 by ethanol precipitation, anion exchange and gel filtration chromatography. The EPS2 and EPS3 were homogeneous with molecular weights of 4.45 × 10⁶ and 2.82 × 10⁶ Da, respectively. All the purified EPS fractions were composed of glucose, galactose, mannose and arabinose, but with different molar ratios. EPS1, EPS2 and EPS3 presented different surface morphologies and their degradation temperatures were 302.7°C, 316.3°C and 316.9°C, respectively. Bioactivity research showed that L. fermentum S1 EPS elicited free radical scavenging capacity and ferric reducing antioxidant power, and 1 mg/mL of EPS significantly improved the gastrointestinal transit tolerance of non EPS-producing strain L. fermentum LG1. Moreover, S1 EPS had a favorable anti-biofilm activity against Escherichia coli and Staphylococcus aureus. These results indicated that S1 EPS could be explored as a promising functional adjunct for application in foods.

A Novel Rhamnose-Rich Hetero-exopolysaccharide Isolated from Lactobacillus paracasei DG Activates THP-1 Human Monocytic Cells

Lactobacillus paracasei DG is a bacterial strain with recognized probiotic properties and is used in commercial probiotic products. However, the mechanisms underlying its probiotic properties are mainly unknown. In this study, we tested the hypothesis that the ability of strain DG to interact with the host is at least partly associated with its ability to synthesize a surface-associated exopolysaccharide (EPS). Comparative genomics revealed the presence of putative EPS gene clusters in the DG genome; accordingly, EPS was isolated from the surface of the bacterium. A sample of the pure EPS from strain DG (DG-EPS), upon nuclear magnetic resonance (NMR) and chemical analyses, was shown to be a novel branched hetero-EPS with a repeat unit composed of l-rhamnose, d-galactose, and N-acetyl-d-galactosamine in a ratio of 4:1:1. Subsequently, we demonstrated that DG-EPS displays immunostimulating properties by enhancing the gene expression of the proinflammatory cytokines tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6), and particularly that of the chemokines IL-8 and CCL20, in the human monocytic cell line THP-1. In contrast, the expression of the cyclooxygenase enzyme COX-2 was not affected. In conclusion, DG-EPS is a bacterial macromolecule with the ability to boost the immune system either as a secreted molecule released from the bacterium or as a capsular envelope on the bacterial cell wall. This study provides additional information about the mechanisms supporting the cross talk between L. paracasei DG and the host.

IMPORTANCE

The consumption of food products and supplements called probiotics (i.e., containing live microbial cells) to potentially prevent or treat specific diseases is constantly gaining popularity. The lack of knowledge on the precise mechanisms supporting their potential health-promoting properties, however, greatly limits a more appropriate use of each single probiotic strain. In this context, we studied a well-known probiotic, Lactobacillus paracasei DG, in order to identify the constitutive molecules that can explain the documented health-promoting properties of this bacterium. We found a novel polysaccharide molecule, named DG-EPS, that is secreted by and covers the bacterium. We demonstrated that this molecule, which has a chemical structure never identified before, has immunostimulatory properties and therefore may contribute to the ability of the probiotic L. paracasei DG to interact with the immune system.

Lactobacillus-produced exopolysaccharides and their potential health benefits: a review

Lactic acid bacteria, such as those of the Lactobacillus genus, naturally reside within the microbiota of the human body and have long been used as starter cultures and probiotic enhancers in fermented foods, such as fermented drinks, yoghurts and cheeses. Many of the beneficial qualities of these bacteria have traditionally been associated with the bacteria themselves, however, a recent spate of studies have demonstrated a wide variety of biological effects exhibited by lactobacilli-produced exopolysaccharides which could, theoretically, confer a range of local and systemic health benefits upon the host. In this review, we discuss the production of exopolysaccharides within the Lactobacillus genus and explore their potential as beneficial bioactive compounds.

Physicochemical characterization of exopolysaccharides produced by Lactobacillus rhamnosus on various carbon sources

The impact of five carbohydrate sources (glucose, maltose, galactose, sucrose, and lactose) on the chemical composition, structure, morphology, and physicochemical properties, as well as, viscosity of exopolysaccharides (EPSs) produced by Lactobacillus rhamnosus E/N was investigated. GLC-MS analysis and 2DNMR spectroscopy showed that the EPSs had the same primary structure independently of the carbon source used in the growth medium. The following EPS composition was elucidated: four rhamnose, two glucose, and one galactose residue with a pyruvate substituent. Molecular masses (M(w)) were determined by gel permeation chromatography, which revealed differences in M(w) distribution. EPS-Gal, EPS-Suc, and EPS-Lac showed heterogenic fractions of a high and low molecular weight, while EPS-Mal and EPS-Glc contained only a high-molecular-weight fraction. AFM microscopy revealed morphological differences in chain length, thickness, and branching. Differences in the Mw ratio and thickness of the polymer chain were correlated with high viscosity of EPS solutions. Our results indicate that a single bacterial strain, depending on the carbon source in the medium, can produce EPSs of different rheological properties.

Isolation of an Exopolysaccharide-producing Bacterium,Sphingomonassp. CS101, Which Forms an Unusual Type of Sphingan

An exopolysaccharide-producing Gram negative bacterium was isolated and determined to be a Sphingomonas sp. (CS101). A sugar composition analysis of an exopolysaccharide indicated that the Sphingomonas sp. CS101 secreted an exopolysaccharide composed of glucose, mannose, fucose, and rhamnose in the ratio of 2.1:1.1:1.0:0.1, suggesting that this exoplysaccharide is an unusual type of sphingan family. The mean molecular weight of the exopolysaccharide was determined to be 4.2x10(5) Da by size exclusion chromatography coupled with multi-angle laser-light scattering (SEC/MALLS) analysis. An exopolysaccharide was produced up to 17 g/l (pH 7; 30 degrees C) with the optimal medium condition over 4 days of cultivation.

Characterization of an extracellular polysaccharide produced by a Pseudomonas strain grown on glycerol

A new extracellular charged polysaccharide composed mainly by galactose, with lower amounts of mannose, glucose and rhamnose, was produced by the cultivation of Pseudomonas oleovorans NRRL B-14682 using glycerol as the sole carbon source. Thermal and solid-state NMR analysis showed that this polymer is essentially amorphous, with a glass transition temperature of 155.7 degrees C. The exopolysaccharide aqueous solutions have viscoelastic properties similar to that of Guar gum, but with affinity to salts as a result of its polyelectrolyte character. In addition, the exopolysaccharide has demonstrated good flocculating and emulsifying properties and film-forming capacity. These properties make this polymer a good alternative to more expensive natural polysaccharides, such as Guar gum, in several applications in the food, pharmaceutical, cosmetic, textile, paper and petroleum industries.

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]

Immunostimulatory polysaccharides from Chlorella pyrenoidosa. A new galactofuranan. measurement of molecular weight and molecular weight dispersion by DOSY NMR

Fractionation of the hot water extract of Chlorella pyrenoidosa was performed using a combination of ethanol precipitation, size exclusion chromatography, and anion exchange chromatography. One fraction contained a new polysaccharide, and this compound was shown to be a 1-->2-linked beta-d-galactofuranan from its 1D and 2D (1)H and (13)C NMR spectra, with a molecular weight of 15 kDa from DOSY NMR measurements. A number of other fractions were shown to have the same repeating unit as the previously identified arabinogalactan. However, arabinogalactans from different fractions were shown by DOSY NMR to have different molecular weights, which ranged from 27 to 1020 kDa. Agreement with molecular weights measured for some of these fractions by SEC-MALS was very good, further confirming the relationship established by Viel et al. between molecular weights of neutral polysaccharides and self-diffusion coefficients. The smaller molecular weight polysaccharides, the galactofuranan and the 27 and 50 kDa arabinogalactans, were shown to be close to monodisperse by analysis of the distributions of the self-diffusion coefficients for the polymers. The larger arabinogalactans had considerable variation in their molecular weights (188 +/- 109 kDa and 1020 +/- 370 kDa). Only the two larger arabinogalactans showed immunostimulatory activity.

Structural characterisation of a highly branched exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB2074

Lactobacillus delbrueckii subsp. bulgaricus NCFB2074 when grown in skimmed milk secretes a highly branched exopolysaccharide. The exopolysaccharide has a heptasaccharide repeat unit and is composed of glucose and galactose in the molar ratio 3:4. Using chemical techniques and 1D and 2D NMR spectroscopy the polysaccharide has been shown to possess the following repeat unit structure: [carbohydrate structure: see text].

Development of an improved procedure for isolation and purification of exopolysaccharides produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483

A method was developed for the isolation and purification of exopolysaccharide (EPS) produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483 that can be adapted for industrial-scale operation. Hydrolyzed milk medium, which was ultrafiltered to remove molecular species larger than 2.5 x 10(5) Da, was found to be a suitable growth medium for the bacteria, which produced approximately 400 mg EPS/l . Optimal isolation of EPS was achieved using centrifugation, filtration and ethanol precipitation methods. Insoluble and soluble EPS fractions were obtained. The soluble fraction was purified using a series of ethanol precipitations to achieve approximately 98% (w/w) purity. This fraction consisted of galactose, glucose, rhamnose and mannose in the ratio of approximately 5:1:0.6:0.5, with traces of glucosamine.

Structural studies of the exopolysaccharide produced by Lactobacillus rhamnosus strain GG (ATCC 53103)

The structure of the extracellular polysaccharide (EPS) from Lactobacillus rhamnosus strain GG has been investigated. In combination with component analysis, NMR spectroscopy shows that the polysaccharide is composed of hexasaccharide repeating units. Sequential information was obtained by two-dimensional (1)H,(1)H-NOESY, and (1)H,(13)C-HMBC NMR techniques. The structure of the repeating unit of the EPS from Lactobacillus rhamnosus strain GG was determined as: [carbohydrate structure: see text]

Structure determination of the exopolysaccharide produced by Lactobacillus rhamnosus strains RW-9595M and R

Exopolysaccharides (EPSs) were isolated and purified from Lactobacillus rhamnosus strains RW-9595M, which has been shown to possess cytokine-stimulating activity, and R grown under various fermentation conditions (carbon source, incubation temperature and duration). Identical (1)H NMR spectra were obtained in all cases. Molecular masses were determined by gel permeation chromatography. The primary structure was elucidated using chemical and spectroscopic techniques. Organic acid, monosaccharide and absolute configuration analyses gave the following composition: pyruvate, 1; D-glucose, 2; D-galactose, 1; and l-rhamnose, 4. Methylation analysis indicated the presence of three residues of 3-linked rhamnose, and one residue each of 2,3-linked rhamnose, 2-linked glucose, 3-linked glucose and 4,6-linked galactose. The EPS was submitted to periodate oxidation followed by borohydride reduction. Monosaccharide analysis of the resulting polysaccharide gave the new composition: rhamnose, 4; and glucose, 1. Methylation analysis confirmed the loss of the 2-linked glucose and 4,6-linked galactose residues. On the basis of one- and two-dimensional (1)H and (13)C NMR data, the structure of the native EPS was consistent with the following heptasaccharide repeating unit: [3Rha alpha-3Glc beta-3[Gal4,6(R)Py alpha-2]Rha alpha-3Rha alpha-3Rha alpha-2Glc alpha-](n) where Rha corresponds to rhamnose (6-deoxymannose) and Py corresponds to pyruvate acetal. Complete (1)H and (13)C assignments are reported for the native and the corresponding pyruvate-hydrolysed polysaccharide. Electrospray MS and MS/MS data are given for the oligosaccharide produced by Smith degradation.

Biosynthesis, characterisation, and design of bacterial exopolysaccharides from lactic acid bacteria

Lactic acid bacteria (LAB) are characterised by their conversion of a large proportion of their carbon feed, fermentable sugars, to lactic acid. However, in addition to lactic acid production, the LAB are able to divert a small proportion of fermentable sugars towards the biosynthesis of exopolysaccharides (EPSs) that are independent of the cell surface and cell wall material. These microbial EPSs when suspended or dissolved in aqueous solution provide thickening and gelling properties, and, as such, there is great interest in using EPSs from food grade microorganisms (such as the LAB that are traditionally used for food fermentations) for use as thickening agents. The current review includes a brief summary of the recent literature describing features of the biosynthetic pathways leading to EPS production. Many aspects of EPS biosynthesis in LAB are still not fully understood and a number of inferences are made regarding the similarity of the pathway to those involved in the synthesis of other cell polysaccharides, e.g., cell wall components. The main body of the review will cover practical aspects concerned with the isolation and characterisation of EPS structures. In the last couple of years, a substantial number of structures have been published and a summary of the common elements of these structures is included as is a suggestion for a system for representing structures. A brief highlight of the attempts that are being made to design 'tailor'-made polysaccharides using genetic modification and control of metabolic flux is presented.

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.

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].