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Characterization of Limosilactobacillus fermentum MC1, the exopolysaccharide-producing strain of human milk microbiota

Lactic acid bacteria (LAB) produce a wide variety of exopolysaccharides (EPSs), high-molecular-mass carbohydrate polymers that are classified as homopolysaccharides or heteropolysaccharides, depending on the sugar composition. LAB-derived EPSs are used as texturizing agents in fermented dairy products. However, novel perspectives are emerging because of their potential functional properties such as protective effects on producer cells, immunomodulatory, anticancer or cholesterol-lowering effects in the host or prebiotic potential among the intestinal microbiota. Therefore, among the 100 bacterial strains isolated from human milk microbiota, we searched for EPS-producing LAB to further characterise their probiotic properties. Only MC1 strain, identified by 16S RNA sequencing as Limosilactobacillus fermentum, showed a ropy phenotype typical for EPS synthesis. Whole-genome analysis of the MC1 genome confirmed the identification, while functional annotation by RAST revealed the genes responsible for EPS production. EPSs were isolated from L. fermentum MC1 strain grown on MRS agar plates for 4 days at 30°C under anaerobic conditions, purified using affinity chromatography and subjected to 1D and 2D NMR spectroscopy for structural analysis. It was shown that MC1 strain produces EPSs that consist of two polysaccharides. The main polysaccharide is composed of -1, 6-linked galactofuranoses with α- glucopyranosyl branched on the second carbon of the main chain, while the determination of second polymer structure is still in progress. L. fermentum MC1 has shown ability to survive under simulated gastrointestinal tract (GIT) conditions. Adhesion of L. fermentum MC1 to the Caco-2 cell monolayer was confirmed by fluorescence microscopy, as well as the potential to reduce adhesion of Escherichia coli 3014 via competitive exclusion mechanism. Further studies will be directed towards the determination of EPS functions related to probiotic effects of MC1 strain.

lactic acid bacteria ; exopolysaccharides ; NMR spectroscopy ; probiotic effects

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