Structural characterisation of two medium molecular mass exopolysaccharides produced by the bacterium Lactobacillus fermentum Lf2

Hafiz Ahmed, Emma Ransom-Jones, Sohaib Sadiq, Ana Vitlic, Neil Mclay, Maria Rojas, Elisa C. Ale, Ana Griselda Binetti, Andrew Collett, Paul Humphreys, Andrew Laws

Research output: Contribution to journalArticle

Abstract

Under optimized conditions, the lactic acid bacterium Lactobacillus fermentum Lf2 secretes up to 2 gL -1 of a mixture of polysaccharides into the fermentation medium when grown on sucrose. Earlier studies had shown that the mixture is biologically active and work was undertaken to characterise the polysaccharides. Preparative size exclusion chromatography was used to separate a high molecular mass β-glucan (weight average mass of 1.23 × 10 6 gmol −1) from two medium molecular mass polysaccharides (weight average mass of 8.8 × 10 4 gmol −1). Under optimized growth conditions, the medium molecular mass polysaccharides accounted for more than 75% of the mixture by weight. Monomer, linkage analysis and NMR spectroscopy of the medium molecular mass polysaccharides, and material isolated after their Smith degradation, was used to identify the structure of the component polysaccharides. The mixture contains two novel polysaccharides. The first has a main chain of β-1,6-linked galactofuranoses which is non-stoichiometrically 2-O-glucosylated. The degree of substitution at the 2-position, with α-D-Glcp, depends on the fermentation conditions; under optimized conditions greater than 80% 2-O-α-D-glucosylation was observed. The second polysaccharide is a heteroglycan with four monosaccharides in the repeat unit: residual signals in the NMR suggest that the sample also contains trace amounts (<3%) of cell wall polysaccharides.

Original languageEnglish
Article number107909
Number of pages7
JournalCarbohydrate Research
Volume488
Early online date10 Jan 2020
DOIs
Publication statusPublished - 1 Feb 2020

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