The Effect Of Three Monosaccharide Carbon Sources On Polysaccharides Synthesis Of Ganoderma Lucidum

Ganoderma lucidum is a large basidiomycete fungus with high nutritional and medicinal value. G. lucidum exopolysaccharide(EPS) is a major valuable metabolite in submerged fermentation. In recent years, the study of G. lucidum polysaccharides focused on the G. lucidum polysaccharide structure and biological activity. However, monosaccharide composition regulated by G. lucidum polysaccharide synthesis pathway was almost ignored. In this study, glucose and other two carbon source, galactose and mannose were all mixed in culture medium to investigate the change of monosaccharide composition and percentage of G. lucidum EPS. Moreover, EPS synthesis enzymes activities and the level of translation were analyzed and the relationship between nucleotide sugar donors and related enzyme activity. The flux of glucose in G. lucidum metabolism and the key enzyme in EPS synthesis was investigated by RT-PCR. The main results were listed as follows:EPS production and dry cell weight(DCW) were tested under mixed carbon source and the results showed that the biomass and EPS production were hardly affected by mixed carbon source. After analyzing the concentration of different carbon source in culture medium, glucose and mannose were more easily utilized by G. lucidum and galactose was slower than other two sugar. The results of monosaccharide composition under different carbon source indicate that the percentage of monosaccharide was greatly affected by the ratio of carbon source in culture medium.The G. lucidum EPS synthesis enzymes activities and monosacchride percentage was correlated. The results indicated that the phosphoglucose isomerase(PGI), phosphomannose isomerase(PMI) and GDP-mannose pyrophosphortlase(GMPPB) were key enzymes which participated in the transformation of mannose from other carbon source under medium without mannose. Meanwhile, a-phosphoglucomutase(a-PGM) was the enzyme catalyzing the synthesis of UDP-galactose in G. lucidum EPS. The express level of various EPS synthesis enzyme encoding gene was different during G. lucidum submerged fermentation. The highest expression of pgm was achieved as the maximum EPS production, while isoenzyme of PMI encoding gene, pmi1 and pmi2, was enhanced by increasing mannose concentration in medium. The analysis of key enzyme expression level provided the effective strategy for enhancing the biological activity of G. lucidum EPS.The anti-tumor activity of G. lucidum EPS obtained under different mixed carbon source was investigated. The results indicated that the anti-tumor activity to A431 and MDA-MB-231 cell line was enhanced by increasing the EPS concentration. Moreover, high percentage of galactose or mannose in G. lucidum EPS was beneficial to the anti-tumor activity to A431 and MDA-MB-231 cells.