The structure of the exopolysaccharide produced by Lactobacillus helveticus 766

Extraction and characterization of an exopolysaccharide from a marine bacterium

The marine bacterial exopolysaccharides (EPS) have transfigured the biotech sector with their myriad applications and prospects. This work was carried out to characterize and analyze the functional and biochemical properties of an EPS (EPS-DR3A) produced by a marine bacterium, Pseudoalteromonas sp. YU16-DR3A. The bacterium was cultured in Zobell marine broth for the production of EPS. The extracted EPS designated as EPS-DR3A was composed of 69% carbohydrates and 7.6% proteins with a molecular weight of 20 kDa. FT-IR spectra showed the presence of different functional groups. The monosaccharide analysis performed using GC-MS showed the presence of fucose, erythrotetrose, ribose, and glucose as monomers. EPS-DR3A showed excellent emulsifying activity against the tested hydrocarbons and food oils with stable emulsions. Rheological analysis of EPS-DR3A revealed the pseudoplastic behavior. The EPS-DR3A displayed good thermal stability with a degradation temperature of 249 °C and a melting point at 322 °C. Further, it had the ability to scavenge DPPH and nitric oxide free radicals with good total antioxidant activity. The in vitro biocompatibility study of EPS-DR3A showed high degree of biocompatibility with human dermal fibroblast cells at the tested concentrations. Taken together, the findings such as thermostability, emulsifying activity, pseudoplasticity, antioxidant activity, and biocompatibility of EPS-DR3A make this biomolecule an important candidate for a wide range of biomedical applications.

Observation of exopolysaccharides (EPS) from Lactobacillus helveticus SBT2171 using the Tokuyasu method

Some species of lactic acid bacteria used for the production of natural cheese produce exopolysaccharides (EPS). Electron microscopy is useful for analyzing the microstructure of EPS produced by lactic acid bacteria. However, pretreatments used to observe the microstructure of EPS by electron microscopy, such as dehydration and resin embedding, can result in EPS flowing out easily from the cell. Therefore, in this study, the Tokuyasu method was conducted on cryosection to reduce EPS outflow. Two types of observation method, namely, using lectin and ruthenium red, were conducted in an attempt to observe EPS produced by Lactobacillus helveticus SBT2171. Observation using the lectin method confirmed that colloidal gold particles conjugated with a lectin recognizing β-galactoside were present in the capsule. Structures that appeared to be β-galactoside-containing slime polysaccharides that were released from the cell wall were also observed. Observation using ruthenium red showed that capsular polysaccharides (CPS) in the capsule were present as a net-like structure. Colloidal gold conjugation with an anti-β-lactoglobulin antibody, in addition to ruthenium red staining, allowed the identification of slime polysaccharides released from the cell wall in the milk protein network derived from the culture medium. Based on these results, the Tokuyasu method was considered to be a useful pretreatment method to clarify and observe the presence of EPS. In particular, both CPS in the capsule and slime exopolysaccharides released from the cell wall were visualized.

Structural characterization of exopolysaccharide from Streptococcus thermophilus ASCC 1275

In this study, we purified and characterized exopolysaccharide (EPS) produced by a high-EPS-producing dairy starter bacterium, Streptococcus thermophilus ASCC 1275. Crude EPS was extracted from S. thermophilus ASCC 1275 and partially purified using dialysis. Further purification and fractionation of exopolysaccharide was conducted using HPLC on a Superose 6 column (Cytiva/Global Life Sciences Solutions, Marlborough, MA). Glycosyl composition analysis, linkage analysis along with 1-dimensional and 2-dimensional nuclear magnetic resonance spectroscopy were performed to deduce the structure of EPS. Three fractions (F) obtained from gel permeation chromatography were termed F1 (2.6%), F2 (45.8%), and F3 (51.6%) with average molecular weights of approximately 511, 40, and 5 kDa, respectively. Monosaccharide composition analysis revealed the dominance of glucose, galactose, and mannose in all 3 fractions. Major linkages observed in F3 were terminal galactopyranosyl (t-Gal), 3-linked glucopyranosyl (3-Glc), 3-linked galactofuranosyl (3-Galf), and 3,6-linked glucopyranosyl (3,6-Glc) and major linkages present in F2 were 4-Glc (48 mol%), followed by terminal mannopyranosyl (t-Man), 2- + 3-linked mannopyranosyl (2-Man+3-Man), and 2,6-linked mannopyranosyl (2,6-Man; total ∼28 mol%). The 1-dimensional and 2-dimensional nuclear magnetic resonance spectroscopy revealed that F2 comprised mannans linked by (1→2) linkages and F3 consisted of linear chains of α-d-glucopyranosyl (α-d-Glcp), β-d-glucopyranosyl (β-d-Glcp), and β-d-galactofuranosyl (β-d-Galf) connected by (1→3) linkages; branching was through (1→6) linkage in F3. A possible structure of EPS in F2 and F3 was proposed.

Genomic Comparison of Lactobacillus helveticus Strains Highlights Probiotic Potential

Lactobacillus helveticus belongs to the large group of lactic acid bacteria (LAB), which are the major players in the fermentation of a wide range of foods. LAB are also present in the human gut, which has often been exploited as a reservoir of potential novel probiotic strains, but several parameters need to be assessed before establishing their safety and potential use for human consumption. In the present study, six L. helveticus strains isolated from natural whey cultures were analyzed for their phenotype and genotype in exopolysaccharide (EPS) production, low pH and bile salt tolerance, bile salt hydrolase (BSH) activity, and antibiotic resistance profile. In addition, a comparative genomic investigation was performed between the six newly sequenced strains and the 51 publicly available genomes of L. helveticus to define the pangenome structure. The results indicate that the newly sequenced strain UC1267 and the deposited strain DSM 20075 can be considered good candidates for gut-adapted strains due to their ability to survive in the presence of 0.2% glycocholic acid (GCA) and 1% taurocholic and taurodeoxycholic acid (TDCA). Moreover, these strains had the highest bile salt deconjugation activity among the tested L. helveticus strains. Considering the safety profile, none of these strains presented antibiotic resistance phenotypically and/or at the genome level. The pangenome analysis revealed genes specific to the new isolates, such as enzymes related to folate biosynthesis in strains UC1266 and UC1267 and an integrated phage in strain UC1035. Finally, the presence of maltose-degrading enzymes and multiple copies of 6-phospho-β-glucosidase genes in our strains indicates the capability to metabolize sugars other than lactose, which is related solely to dairy niches.

'Ropy' phenotype, exopolysaccharides and metabolism: Study on food isolated potential probiotics LAB

Lactic acid bacteria are fully recognized for their industrial applications among which the production and release of exopolysaccharides. In the present investigation, we screened fifteen Lactobacilli in order to find ropy strains, quantify exopolysaccharides and detect proteins specifically associated with the ropy-exopolysaccharide production. The highest ropy-exopolysaccharide producer (L. helveticus 6E8), was grown in stimulating and basal condition (10% and 2% lactose) and subjected to comparative proteomic analysis. The levels of 4 proteins were found significantly increased in the membrane fraction under stimulating conditions: a specific exopolysaccharide biosynthetic protein, a stress-induced protein, a protein involved in secretion and an ATP-synthase subunit. Conversely, several enzymes involved in anabolism and protein synthesis were decreased. These results suggest a general shift from growth to exopolysaccharide-mediated protection from the hyperosmotic environment. Due to the great interest in exopolysaccharides with novel features, the identification of these proteins could have implications for future improvements of industrial strains.

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]

Culture conditions determine the balance between two different exopolysaccharides produced by Lactobacillus pentosus LPS26

Lactobacillus pentosus LPS26, isolated from a natural fermentation of green olives, produces a capsular polymer constituted of two exopolysaccharides (EPS): EPS A, a high-molecular-weight (high-Mw) polysaccharide (1.9x10(6) Da) composed of glucose and rhamnose (3:1), and EPS B, a low-Mw polysaccharide (3.3x10(4) Da) composed of glucose and mannose (3:1). Fermentation experiments in a chemically semidefined medium with different carbon sources (glucose, fructose, mannitol, and lactose) showed that all of them except fructose supported EPS A production rather than EPS B production. The influence of temperature and pH was further analyzed. As the temperature dropped, increased synthesis of both EPS was detected. The control of pH especially enhanced EPS B production. With regard to this, the maximum total EPS production (514 mg liter-1) was achieved at a suboptimal growth temperature (20 degrees C) and pH 6.0. Continuous cultures showed that EPS A, synthesized mainly at low dilution rates, is clearly dependent on the growth rate, whereas EPS B synthesis was hardly affected. EPS production was also detected in supplemented skimmed milk, but no increase on the viscosity of the fermented milk was recorded. This could be linked to the high proportion of the low-Mw polysaccharide produced in these conditions in contrast to that observed in culture media. Overall, the present study shows that culture conditions have a clear impact on the type and concentration of EPS produced by strain LPS26, and consequently, these conditions should be carefully selected for optimization and application studies. Finally, it should be noted that this is, to our knowledge, the first report on EPS production by L. pentosus.

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].

Biodiversity of exopolysaccharides produced by Streptococcus thermophilus strains is reflected in their production and their molecular and functional characteristics

Twenty-six lactic acid bacterium strains isolated from European dairy products were identified as Streptococcus thermophilus and characterized by bacterial growth and exopolysaccharide (EPS)-producing capacity in milk and enriched milk medium. In addition, the acidification rates of the different strains were compared with their milk clotting behaviors. The majority of the strains grew better when yeast extract and peptone were added to the milk medium, although the presence of interfering glucomannans was shown, making this medium unsuitable for EPS screening. EPS production was found to be strain dependent, with the majority of the strains producing between 20 and 100 mg of polymer dry mass per liter of fermented milk medium. Furthermore, no straightforward relationship between the apparent viscosity and EPS production could be detected in fermented milk medium. An analysis of the molecular masses of the isolated EPS by gel permeation chromatography revealed a large variety, ranging from 10 to >2,000 kDa. A distinction could be made between high-molecular-mass EPS (>1,000 kDa) and low-molecular-mass EPS (<1,000 kDa). Based on the molecular size of the EPS, three groups of EPS-producing strains were distinguished. Monomer analysis of the EPS by high-performance anion-exchange chromatography with amperometric detection was demonstrated to be a fast and simple method. All of the EPS from the S. thermophilus strains tested were classified into six groups according to their monomer compositions. Apart from galactose and glucose, other monomers, such as (N-acetyl)galactosamine, (N-acetyl)glucosamine, and rhamnose, were also found as repeating unit constituents. Three strains were found to produce EPS containing (N-acetyl)glucosamine, which to our knowledge was never found before in an EPS from S. thermophilus. Furthermore, within each group, differences in monomer ratios were observed, indicating possible novel EPS structures. Finally, large differences between the consistencies of EPS solutions from five different strains were assigned to differences in their molecular masses and structures.

Unusual organization for lactose and galactose gene clusters in Lactobacillus helveticus

The nucleotide sequences of the Lactobacillus helveticus lactose utilization genes were determined, and these genes were located and oriented relative to one another. The lacLM genes (encoding the beta-galactosidase protein) were in a divergent orientation compared to lacR (regulatory gene) and lacS (lactose transporter). Downstream from lacM was an open reading frame (galE) encoding a UDP-galactose 4 epimerase, and the open reading frame had the same orientation as lacM. The lacR gene was separated from the downstream lacS gene by 2.0 kb of DNA containing several open reading frames that were derived from fragmentation of another permease gene (lacS'). Northern blot analysis revealed that lacL, lacM, and galE made up an operon that was transcribed in the presence of lactose from an upstream lacL promoter. The inducible genes lacL and lacM were regulated at the transcriptional level by the LacR repressor. In the presence of glucose and galactose galE was transcribed from its promoter, suggesting that the corresponding enzyme can be expressed constitutively. Lactose transport was inducible by addition of lactose to the growth medium.

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.

Modeling of the structure in aqueous solution of the exopolysaccharide produced by Lactobacillus helveticus 766

A method is described for constructing a conformational model in water of a heteropolysaccharide built up from repeating units, and is applied to the exopolysaccharide produced by Lactobacillus helveticus 766. The molecular modeling method is based on energy minima, obtained from molecular mechanics calculations of each of the constituting disaccharide fragments of the repeating unit in vacuo, as starting points. Subsequently, adaptive umbrella sampling of the potential of mean force is applied to extract rotamer populations of glycosidic dihedral angles of oligosaccharide fragments in solution. From these analyses, the most probable conformations are constructed for the hexasaccharide-repeating unit of the polysaccharide. After exploring the conformational space of each of the individual structures by molecular dynamics simulations, the different repeating unit conformations are used as building blocks for the generation of oligo- and polysaccharide models, by using a polysaccharide building program. The created models of the exopolysaccharide produced by L. helveticus 766 exhibit a flexible twisted secondary structure and tend to adopt a random coil conformation as tertiary structure.

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.

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].

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.

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.

Structure of an extracellular polysaccharide produced by Lactobacillus rhamnosus strain C83

The extracellular polysaccharide produced by Lactobacillus rhamnosus strain C83 was found to be composed of D-glucose and D-galactose in a molar ratio of 2:3. The primary structure of the polysaccharide was shown by sugar analysis, methylation analysis, FABMS, partial acid hydrolysis and nuclear magnetic resonance (NMR) spectroscopy to consist of a pentasaccharide repeating unit having the following structure: -->3)-alpha-D-Glcp-(1-->2)-beta-D-Galf-(1-->6)-alpha-D-Galp-(1-->6 )-alpha-D -Glcp-(1-->3)-beta-D-Galf-(1-->

Mutational analysis of exopolysaccharide biosynthesis by Lactobacillus sakei 0-1

Lactobacillus sakei strain 0-1 produces an exopolysaccharide (EPS) consisting of glucose and rhamnose in a ratio of 3:2. As part of a biochemical and molecular analysis of the EPS biosynthetic pathway in L. sakei strain 0-1, we have isolated a random set of EPS-negative mutants. Following treatment of cells with the mutagen ethylmethane sulfonic acid, a total of 10 mutants were identified that lacked the clear ropy appearance of wild-type colonies on agar plates. Their characterization revealed that eight mutants had completely lost the ability to synthesize the normal EPS. Six of these mutants lacked activities of enzymes involved in the biosynthesis of dTDP-rhamnose, required for EPS production. Only mutant strains 12 and 20 were directly affected in EPS synthesis. Strain 12 synthesized EPS with a different sugar composition, however. Interestingly, strain 12 showed temperature-dependent EPS synthesis, with the highest amounts synthesized at 12 degrees C, and low amounts at the optimal temperature for growth (30 degrees C). Two mutants were in fact EPS-positive, producing the normal EPS, but displayed a different cell morphology (elongated cells), indicating a modification in cell wall synthesis.

The exopolysaccharides produced by Streptococcus thermophilus Rs and Sts have the same repeating unit but differ in viscosity of their milk cultures

The polysaccharides produced by Streptococcus thermophilus Rs and Sts in skimmed milk consist of D-Gal and L-Rha in a molar ratio of 5:2. Linkage analysis and 1D/2D NMR (1H and 13C) studies revealed that both polysaccharides have the same branched heptasaccharide repeating unit: [formula: see text] Remarkably, the two strains differ in their effects on the viscosity of stirred milk cultures. The milk culture of S. thermophilus Rs is non-ropy and affords 135 mg/L polysaccharide with an average molecular mass of 2.6 x 10(3) kDa. In contrast, the milk culture of S. thermophilus Sts is ropy and produces 127 mg/L polysaccharide with an average molecular mass of 3.7 x 10(3) kDa. Permeability measurements of non-stirred milk cultures of both strains suggest that both strains have a similar effect on the protein-polysaccharide network. Therefore, the only clear difference between both strains, which may cause the difference in ropiness of the milk cultures, is the difference in molecular mass of the polysaccharide.

Structural characterization of the exocellular polysaccharides produced by Streptococcus thermophilus SFi39 and SFi12

We investigated the structures of the exopolysaccharides (EPSs) produced by Streptococcus thermophilus SFi39 and SFi12. Both polymers were found to have molecular masses of greater than 2 x 10(6) Da. The SFi39 EPS consisted of D-glucose and D-galactose in a molar ratio of 1:1, whereas the SFi12 EPS was composed of D-galactose, L-rhamnose, and D-glucose in a molar ratio of 3:2:1. Methylation analysis of and nuclear magnetic resonance spectra recorded from the native polysaccharide, as well as oligosaccharides released by partial acid hydrolysis, allowed the complete structural determination of the SFi39 EPS, which consists of the following tetrasaccharide repeating unit: [formula: see text] Similar spectra recorded only from the native polysaccharide were sufficient to allow the structural determination of the SFi12 EPS, which consists of the following hexasaccharide repeating unit: [formula: see text] This study shows that the texturizing properties of different S. thermophilus ropy strains are based on the production of EPSs exhibiting chemical similarities but structural differences.

Structural characterisation of the exocellular polysaccharide produced by Streptococcus thermophilus OR 901

The exocellular polysaccharide of Streptococcus thermophilus OR 901, isolated from partially deproteinised whey, is a heteropolymer of D-galactopyranose and L-rhamnopyranose residues in the molar ratio 5:2. The structure was established by methylation analysis and 1D and 2D NMR spectroscopy of the native polysaccharide, in combination with characterisation of oligosaccharide fragments, obtained by partial acid hydrolysis, using methylation analysis and 1D 1H NMR spectroscopy. The polysaccharide has a branched heptasaccharide repeating unit with the following structure: [sequence: see text]

Predicting helical structures of the exopolysaccharide produced by Lactobacillus sake 0- 1

The viscous exopolysaccharide (EPS) produced by Lactobacillus sake 0- 1 is a high molecular mass polymer (Mm 6 x 10(6) Da) consisting of pentasaccharide repeating units with a composition of D-glucose, L-rhamnose, and sn-glycerol 3-phosphate in molar ratios of 3:2:1. One of the rhamnose residues in the repeating unit is partially 2-O-acetylated. The O-deacetylated, deglycerophosphorylated EPS has been investigated by molecular mechanics calculations. A complete conformational analysis of each of the constituent disaccharide fragments has been performed using the flexible residue approach with the MM3(92) force field. Furthermore, using the same force field, CICADA analyses were accomplished on hexa- and octasaccharide substructure of the polysaccharide. Based on these analyses, insight was obtained into nine conformational minima for the polysaccharide. The low energy conformations found by CICADA were extrapolated to regular polysaccharide structures using a polysaccharide builder program. The generated helices exhibit either 2-fold or 3- or 4-fold right-handed chiralities, and in each case the helices are highly extended.

Structural characterization of the exopolysaccharide produced by Lactobacillus acidophilus LMG9433

The exopolysaccharide produced by Lactobacillus acidophilus LMG9433 in a semi-defined medium was found to be a charged heteropolymer, with a composition of D-glucose, D-galactose, D-glucuronic acid, and 2-acetamido-2-deoxy-D-glucose in molar ratios of 2:1:1:1. By means of methylation analysis, uronic acid degradation, de-N-acetylation/deamination, partial acid hydrolysis, and 1D/2D NMR studies the polysaccharide was demonstrated to consist of repeating units with the following structure: [Table: see text]

Structural studies of the exopolysaccharide produced by Lactobacillus paracasei 34-1

The exopolysaccharide produced by Lactobacillus paracasei 34-1 in a semi-defined medium was found to be a heteropolymer, composed of D-galactose, 2-acetamido-2-deoxy-D-galactose, and sn-glycerol 3-phosphate in molar ratios of 3:1:1. By means of deglycerophosphorylation, methylation analysis, and 1D/2D NMR studies (1H, 13C, and 31P) the polysaccharide was shown to consist of repeating units with the following structure: [formula: see text].

Identification and characterization of the eps (Exopolysaccharide) gene cluster from Streptococcus thermophilus Sfi6

We report the identification and characterization of the eps gene cluster of Streptococcus thermophilus Sfi6 required for exopolysaccharide (EPS) synthesis. This report is the first genetic work concerning EPS production in a food microorganism. The EPS secreted by this strain consists of the following tetrasaccharide repeating unit:-->3)-beta-D-Galp-(1-->3)-[alpha-D-Galp-(1-->6)]-beta-D- D-Galp-(1-->3)-alpha-D-Galp-D-GalpNAc-(1-->. The genetic locus The genetic locus was identified by Tn916 mutagenesis in combination with a plate assay to identify Eps mutants. Sequence analysis of the gene region, which was obtained from subclones of a genomic library of Sfi6, revealed a 15.25-kb region encoding 15 open reading frames. EPS expression in the non-EPS-producing heterologous host, Lactococcus lactis MG1363, showed that within the 15.25-kb region, a region with a size of 14.52 kb encoding the 13 genes epsA to epsM was capable of directing EPS synthesis and secretion in this host. Homology searches of the predicted proteins in the Swiss-Prot database revealed high homology (40 to 68% identity) for epsA, B, C, D, and E and the genes involved in capsule synthesis in Streptococcus pneumoniae and Streptococcus agalactiae. Moderate to low homology (37 to 18% identity) was detected for epsB, D, F, and H and the genes involved in capsule synthesis in Staphylococcus aureus for epsC, D, and E and the genes involved in exopolysaccharide I (EPSI) synthesis in Rhizobium meliloti for epsC to epsJ and the genes involved in lipopolysaccharide synthesis in members of the Enterobacteriaceae, and finally for eps K and lipB of Neisseria meningitidis. Genes (epsJ, epsL, and epsM) for which the predicted proteins showed little or no homology with proteins in the Swiss-Prot database were shown to be involved in EPS synthesis by single-crossover gene disruption experiments.