Isolation and identification of endophytic fungi from Boletus speciosus and optimization of fermentation conditions for exopolysaccharides production

Endophytic fungus producing exopolysaccharides was isolated from the fruiting body of Boletus speciosus, and the screened strain was identified through morphological observation and molecular biology technigues. The effects of fermentation medium and fermentation conditions on the exopolysaccharides production of the screened strain were studied by single-factor experiments with exopolysaccharide production as an evaluation indicator. Based on the results of the single factor experiments, the fermentation conditions that significantly affected the production of extracellular polysaccharides were optimized through response surface tests. The results showed that an exopolysaccharides producing strain was screened and named XY, and it was identified as Hypomyces chlorinigenus. The optimal fermentation medium formula was glucose 4%, soybean meal 3%, KH₂PO₄ 0.25%, CaCl₂ 0.05%. The optimal fermentation conditions were fermentation temperature 24 ℃, shaking speed 190 r/min, inoculum 8% (V/V), liquid loading volume 100 ml/250 ml and fermentation time 6.5 d. Under these conditions, the polysaccharide yield reached 36.04 mg/ml.