Biotransformation of Host Plant Flavonoids by the Fungal Endophyte Epicoccum nigrum

Fermentation of the fungus Epicoccum nigrum isolated from leaves of Salix sp. on green lentil solid medium yielded the flavonol kaempferol (3) as well as two kaempferol O-diglyco-sides (1 and 2) including the new compound 1. The fungal flavonoids bear strong structural similarities to kaempferol derivatives such as kaempferol O-glycoside (4) being present in green lentils. Furthermore, feeding experiments were conducted by adding flavonoids (kaempferol and rutin) as precursors to solid rice media followed by HPLC and LC-MS analyses. Fermentation of the fungus on flavonoid free solid rice medium afforded flavonoid free extracts indicating that the fungal flavonoids originate through hydrolytic cleavage of kaempferol glycosides such as 4 followed by glycosylation and acetylation. This study suggests that E. nigrum is capable of biotransformation reactions of plant derived flavonoids whereas de novo biosynthesis of flavonoids is less likely.