Structural investigation of an exopolysaccharide substituted with a lactyl ether group produced by Raoultella terrigena Ez-555-6 isolated in the Chernobyl exclusion zone

Raoultella terrigena strain Ez-555-6, isolated from a root nodule of Medicago sativa harvested in the Chernobyl exclusion zone, produces a non-referenced high-molecular-mass exopolysaccharide (EPS). The structure of this EPS was determined using a combination approach including monosaccharide composition (GLC–FID, HPAEC–PAD), determination of glycosylation sites (GLC–EIMS) and 1D/2D NMR (1H, 13C) and ESIMS (HR, MS/MS) studies of oligosaccharides obtained from mild acid hydrolysis. The EPS was found to be a charged pentasaccharide with a repeating unit composed of d-galactose, d-glucose, d-mannose and d-glucuronic acid (1:2:1:1). Lactic acid and O-acetyl substituents were localized on galactose and glucose residues, respectively, as presented in the following structure:Figure optionsDownload full-size imageDownload as PowerPoint slide

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