Three exopolysaccharides of the β-(1→6)-d-glucan type and a β-(1→3;1→6)-d-glucan produced by strains of Botryosphaeria rhodina isolated from rotting tropical fruit

Four exopolysaccharides (EPS) obtained from Botryosphaeria rhodina strains isolated from rotting tropical fruit (graviola, mango, pinha, and orange) grown on sucrose were purified on Sepharose CL-4B. Total acid hydrolysis of each EPS yielded only glucose. Data from methylation analysis and 13C NMR spectroscopy indicated that the EPS from the graviola isolate consisted of a main chain of glucopyranosyl (1→3) linkages substituted at O-6 as shown in the putative structure below:Figure optionsDownload full-size imageDownload as PowerPoint slideThe EPS of the other fungal isolates consisted of a linear chain of (1→6)-linked glucopyranosyl residues of the following structure:Figure optionsDownload full-size imageDownload as PowerPoint slideFTIR spectra showed one band at 891 cm−1, and 13C NMR spectroscopy showed that all glucosidic linkages were of the β-configuration. Dye-inclusion studies with Congo Red indicated that each EPS existed in a triple-helix conformational state. β-(1→6)-d-Glucans produced as exocellular polysaccharides by fungi are uncommon.

Graphical abstractPutative structure of β-(1→3,1→6)-d-glucan Structure of β-(1→6)-d-glucanFigure optionsDownload full-size imageDownload as PowerPoint slide