cremoris LC330

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].

Influence of different substrate limitations on the yield, composition and molecular mass of exopolysaccharides produced by Lactococcus lactis subsp. cremoris in continuous cultures

The type of substrate limitation had a remarkable influence on the molecular mass of exopolysaccharides (EPS) produced by Lactococcus lactis subsp. cremoris NIZO B40 and NIZO B891. Under glucose/energy limitation, the molecular mass was much smaller than under leucine or phosphate limitation, resulting in a marked decrease of the intrinsic viscosity of this EPS. The sugar composition of EPS produced by both strains, and the phosphate content of EPS produced by NIZO B40, were not affected by the type of nutrient limitation. Both strains produced comparable amounts of EPS under leucine and glucose limitation, but the efficiency of EPS production was highest under glucose limitation. The EPS yields of the phosphorylated B40 EPS as well as the unphosphorylated B891 EPS were reduced, with about 40% under conditions of phosphate limitation.

Production of exopolysaccharide by Lactobacillus rhamnosus R and analysis of its enzymatic degradation during prolonged fermentation

The potential of Lactobacillus rhamnosus R for producing exopolysaccharide (EPS) when grown on basal minimum medium supplemented with glucose or lactose was investigated. EPS production by L. rhamnosus R is partially growth associated and about 500 mg of EPS per liter was synthesized with both sugars. The product yield coefficient (Y(EPS/S)) was 3.15 (0.0315 g of EPS [g of lactose](-1)) and 2.88 (0.0288 g of EPS [g of glucose](-1)). It was clearly shown that the amount of EPS produced declined upon prolonged fermentation. Degradation of EPS in fermentation processes was also assessed by measuring its molecular weights and viscosities. As these reductions might have a negative effect on the yield and viscosifying properties of EPS, it was essential to examine possible causes related to this breakdown. The decrease in viscosities and molecular weights of EPS withdrawn at different cultivation times permitted us to suspect the presence of a depolymerizing enzyme in the fermentation medium. Our study on enzymatic production profiles showed a large spectrum of glycohydrolases (alpha-D-glucosidase, beta-D-glucosidase, alpha-D-galactosidase, beta-D-galactosidase, beta-D-glucuronidase, and some traces of alpha-L-rhamnosidase). These enzymes were localized, two of them (alpha-D-glucosidase and beta-D-glucuronidase) were partially purified and characterized. When incubated with EPS, these enzymes were capable of lowering the viscosity of the polymer as well as liberating some reducing sugars. Upon prolonged incubation (27 h), the loss of viscosity was increased up to 33%.

Production of Exopolysaccharide by Lactobacillus rhamnosus R and Analysis of Its Enzymatic Degradation during Prolonged Fermentation

The potential of Lactobacillus rhamnosus R for producing exopolysaccharide (EPS) when grown on basal minimum medium supplemented with glucose or lactose was investigated. EPS production by L. rhamnosus R is partially growth associated and about 500 mg of EPS per liter was synthesized with both sugars. The product yield coefficient ( Y EPS/S ) was 3.15 (0.0315 g of EPS [g of lactose] −1 ) and 2.88 (0.0288 g of EPS [g of glucose] −1 ). It was clearly shown that the amount of EPS produced declined upon prolonged fermentation. Degradation of EPS in fermentation processes was also assessed by measuring its molecular weights and viscosities. As these reductions might have a negative effect on the yield and viscosifying properties of EPS, it was essential to examine possible causes related to this breakdown. The decrease in viscosities and molecular weights of EPS withdrawn at different cultivation times permitted us to suspect the presence of a depolymerizing enzyme in the fermentation medium. Our study on enzymatic production profiles showed a large spectrum of glycohydrolases (α- d -glucosidase, β- d -glucosidase, α- d -galactosidase, β- d -galactosidase, β- d -glucuronidase, and some traces of α- l -rhamnosidase). These enzymes were localized, two of them (α- d -glucosidase and β- d -glucuronidase) were partially purified and characterized. When incubated with EPS, these enzymes were capable of lowering the viscosity of the polymer as well as liberating some reducing sugars. Upon prolonged incubation (27 h), the loss of viscosity was increased up to 33%.

Growth associated exopolysaccharide expression in Lactococcus lactis subspecies cremoris Ropy352

A natural lactococcal isolate, Lactococcus lactis ssp. cremoris Ropy352, has been previously shown to express two phenotypically distinct exopolysaccharides (ropy and mucoid). This natural isolate was cultured on various media to explore the carbon requirements for exopolysaccharide expression. Ropy exopolysaccharide expression was optimal when grown in defined media rather than on M17-based media. Ropy352 was examined for inducible lysogenic phages. No lytic burst was observed in Ropy352 with ultraviolet light or mitomycin C for phage induction. The sugar compositions of the two phenotypically distinct exopolysaccharides were determined. The ropy exopolysaccharide is composed of galactose and glucose in the molar percents of 42 and 58%, respectively. The mucoid exopolysaccharide is composed of galactose, glucose, and mannose in the molar percents of 58, 29, and 13%, respectively. Mutational analysis revealed that mutations impairing ropy exopolysaccharide expression but not affecting mucoid exopolysaccharide expression could be isolated.

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.

Influence of reduced water activity on lactose metabolism by lactococcus lactis subsp. cremoris At different pH values

The influence of reduced water activity (aw) on lactose metabolism by Lactococcus lactis subsp. cremoris 2254 and 2272 was studied at different pH values. In control incubations (aw, 0.99) with nongrowing cells in pH-controlled phosphate buffer, the levels of carbon recovered as L-(+)-lactate were 92% at pH 6.1 and 5.3 and 78% at pH 4.5. However, the levels of recovery decreased to approximately 50% at all pH values tested when the aw was 0.88 (with glycerol as the humectant). When growing cells in broth controlled at pH 6.3 were used, a reduction in the aw from 0.99 to 0.96 resulted in a decrease in the level of lactose carbon recovered as L-(+)-lactate from 100 to 71%. Low levels of L-(+)-lactate carbon recovery (<50%) were also observed with cells resuspended in pH-uncontrolled reconstituted skim milk at aw values of 0.99 and 0. 87 and in young cheese curds. The missing lactose carbon could not be accounted for by acetate, ethanol, formate, acetaldehyde, or pyruvate. Attempts were made to determine where the missing lactose carbon was diverted to under the stress conditions used. Some of the missing lactose carbon was recovered as galactose (0.1 to 2.5 mM) in culture supernatants. Decreasing either the aw or the pH resulted in increased galactose accumulation by nongrowing cells; adjusting both environmental factors together potentiated the effect. The sensitivities of the two lactococcal strains tested were different; strain 2272 was more prone to accumulate galactose under stress conditions. A methyl pentose(s) and additional galactose were found in acid-hydrolyzed supernatants from cultures containing both growing and nongrowing cells, indicating that a saccharide(s) rich in these components was formed by lactococci under low-aw and low-pH stress conditions.