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

Abstract

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 EPSD1-72, EPSD1-96 and EPSD1-168) 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 (EPSD1-72), 15.4 ± 2.2 (EPSD1-96) and 14.8 ± 1.8 (EPSD1-168). The EPSD1-72 had high protein content (28.5%) and only 71% of carbohydrate; while EPSD1-96 and EPSD1-168 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 EPSD1-168. Differently, EPSD1-96 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.