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Title

Comparative analysis of Leuconostoc and Weissella dextran producing strains isolated from Tunisia

AuthorsBesrour-Aouam, Norhane; Hernández-Alcántara, Annel M. ; Prieto, Alicia ; Mohedano Bonillo, Mari Luz ; Imene, Fhoula; Ruas-Madiedo, Patricia ; Najjari, Afef; Ouzari, Hadda-Imene; López, Paloma
KeywordsDextran
Leuconostoc lactis
Weissella
EPS
Bacterial adhesion
Issue Date17-Jun-2019
Citation13ª Reunión RedBAL (2019)
AbstractMany lactic acid bacteria (LAB) produce exopolysaccharides (EPS) and, among these, dextrans with high molecular mass have interest for the food industry, due to their rheological and immunomodulatory properties. In this work, four LAB, Leuconostoc lactis AV1n, Weissella cibaria AV2ou, Weissella confusa 11.3b and V30 strains, were chosen from a collection of EPSproducing LAB isolated in Tunisia from different habitats, with the aim of characterizing their EPS production at different levels: (i) the polymer itself, (ii) the bacterial metabolic fluxes linked to the dextran production, and (iii) the influence of the EPS in the adhesion properties of their producing LAB. The characterization of the EPS was performed by analysis of their monosaccharide composition, infrared spectrum and methylation analysis in order to determine the O-glycosidic linkages. Molecular weight was investigated by size exclusion chromatography coupled with multiangle laser light scattering detection (SEC-MALLS). Quantification of dextran production was performed by the phenol-sulfuric method, and metabolic fluxes were analysed by GC-MS. The ability of the strain to adhere to epithelial intestinal cells was tested in vitro by performing bacteria-Caco-2 cells interaction assays. Dextranase activity was investigated by halo formation on MRS agar plates supplemented with 0.4% of dextran blue. The four LAB were able to produce EPS in medium supplemented with sucrose. Purification and physicochemical characterization of the EPS revealed that they were dextrans with a main chain of glucopyranose units with α-(1,6) linkages (between 90.4% and 94.0%) and partially branched in the O-3 position by a single α-glucopyranose unit (between 6.0% and 9.6%). The molecular masses of the dextrans ranged between 5.84 × 107 Da and 2.61 × 108 Da. The growing chain of dextrans, composed of glucose molecules, is synthesized extracellularly by dextransucrases by hydrolysis of sucrose with release of fructose, which could be internalised and further metabolised to lactate. The metabolic analysis revealed that, production of the four EPS took place only during exponential growth, and increase of lactate concentration in culture supernatants was observed during both the exponential and the stationary phases of growth. However, the four bacteria showed a different pattern of coupling of EPS production and metabolic fluxes. At the beginning of the stationary phase of growth, L. lactis AV1n consumed >95% of the sucrose, whereas around 57% of the disaccharide was still present in supernatants of the three Weissella strains. Correlating with these results, differences in transient accumulation and further decrease of fructose in culture supernatants was observed. In addition, during the stationary phase there was a significant decrease in the recovery of EPS from supernatants of W. confusa 11.3b cultures. This result indicated the existence of a dextranase activity, and this hypothesis was supported by the ability of the strain to generate halos on MRS agar plates supplemented with dextran blue. Studies of the LAB-Caco-2 cell interactions revealed that L. lactis AV1n was the only bacterium able to adhere to the enterocytes with a higher level in the presence of 47% sucrose (when dextran is produced), than of 27% glucose. As far as we know, this is the first instance of a positive effect of dextran on adhesion, not detected for the other Tunisian LAB or other bacteria from different origins. strains and in other previous works. This and our previous results revealing probiotic properties (Fhoula et al. Biomed Res Int 1654151, 2018; Besrour-Aouam et al. Front Microbiol 10:959, 2019;) indicate that, among the strains tested, L. lactis AV1n and W. confusa 11.3b are the most suitable for production of functional food
DescriptionTrabajo presentado en la 13ª Reunión de la Red Española de Bacterias Lácticas (RedBAL), celebrada en Madrid (España) del 17 al 18 de junio de 2019
URIhttp://hdl.handle.net/10261/208658
Appears in Collections:(IPLA) Comunicaciones congresos
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