Flavonolignans from <i>Aspergillus iizukae</i>, a Fungal Endophyte of Milk Thistle (<i>Silybum marianum</i>)

Abstract

Silybin A (<b>1</b>), silybin B (<b>2</b>), and isosilybin A (<b>3</b>), three of the seven flavonolignans that constitute silymarin, an extract of the fruits of milk thistle (<i>Silybum marianum</i>), were detected for the first time from a fungal endophyte, <i>Aspergillus iizukae</i>, isolated from the surface-sterilized leaves of <i>S. marianum</i>. The flavonolignans were identified using a UPLC-PDA-HRMS-MS/MS method by matching retention times, HRMS, and MS/MS data with authentic reference compounds. Attenuation of flavonolignan production was observed following successive subculturing of the original flavonolignan-producing culture, as is often the case with endophytes that produce plant-based secondary metabolites. However, production of <b>1</b> and <b>2</b> resumed when attenuated spores were harvested from cultures grown on a medium to which autoclaved leaves of <i>S. marianum</i> were added. The cycle of attenuation followed by resumed biosynthesis of these flavonolignans was replicated in triplicate