Influence of carbon and nitrogen sources on structural features and immunomodulatory activity of exopolysaccharides from Ganoderma lucidum

Abstract

In this work, the effects of various carbon and nitrogen sources on structural features and immunomodulatory activity of exopolysaccharides (EPS) from Ganoderma lucidum were studied. When glucose and yeast powder were used as carbon and nitrogen sources, the apparent viscosity of fermentation broth and EPS yield and the corresponding sugar content were higher than those cultured with other carbon and nitrogen sources. The main polysaccharide components (20E) with molecular weights ranging from 2.78 × 106 to 3.96 × 106 g/mol were isolated from fermentation broth through 20% ethanol precipitation. Monosaccharide analysis showed that the carbon source significantly affected the monosaccharide compositions of 20E, and the initial carbon source of the medium accounted for the largest proportion of monosaccharide in 20E. The immunoenhancing activities on inducing NF-κB activation by 20E fractions from different carbon and nitrogen combinations exhibited significant differences. Correlation analysis demonstrated that the immunomodulatory activity of 20E fractions was positively correlated with sugar contents and the molar ratios of glucose, while it was negatively correlated with the molar ratios of xylose. As the structural features and biological activities of EPS are highly dependent on the polysaccharide medium composition, this variability can be used advantageously to produce tailor-made polysaccharides with specific applications.