Screening of endophytic sources of exopolysaccharides: Preliminary characterization of crude exopolysaccharide produced by submerged culture of Diaporthe sp. JF766998 under different cultivation time

Endophytic fungi have been described as producers of important bioactive compounds; however, they remain under-exploited as exopolysaccharides (EPS) sources. Therefore, this work reports on EPS production by submerged cultures of eight endophytes isolated from Piper hispidum Sw., belonging to genera Diaporthe, Marasmius, Phlebia, Phoma, Phyllosticta and Schizophyllum. After fermentation for 96 h, four endophytes secreted EPS: Diaporthe sp. JF767000, Diaporthe sp. JF766998, Diaporthe sp. JF767007 and Phoma herbarum JF766995. The EPS from Diaporthe sp. JF766998 differed statistically from the others, with a higher percentage of carbohydrate (91%) and lower amount of protein (8%). Subsequently, this fungus was grown under submerged culture for 72, 96 and 168 h (these EPS were designated EPS_D1-72, EPS_D1-96 and EPS_D1-168) and the differences in production, monosaccharide composition and apparent molecular were compared. The EPS yields in mg/100 mL of culture medium were: 3.0 ± 0.4 (EPS_D1-72), 15.4 ± 2.2 (EPS_D1-96) and 14.8 ± 1.8 (EPS_D1-168). The EPS_D1-72 had high protein content (28.5%) and only 71% of carbohydrate; while EPS_D1-96 and EPS_D1-168 were composed mainly of carbohydrate (≈95 and 100%, respectively), with low protein content (≈5%) detected at 96 h. Galactose was the main monosaccharide component (30%) of EPS_D1-168. Differently, EPS_D1-96 was rich in glucose (51%), with molecular weight of 46.6 kDa. It is an important feature for future investigations, because glucan-rich EPS are reported as effective antitumor agents.