Detoxification of Ustiloxin A by Hydroxylation of Endophytic Fungus Petriella setifera Nitaf10

Ustiloxins are a kind of cyclopeptide mycotoxins produced by rice false smut pathogen Villosiclava virens, which seriously threatens the safe production of rice and health of humans and animals. Hydroxylation, a biotransformation reaction that regio- and stereoselectively introduces a hydroxyl group into the molecule catalyzed by the hydroxylase produced by organisms, has been considered an efficient way to detoxify mycotoxins. In this study, the endophytic fungus Petriella setifera Nitaf10 was found to be able to detoxify ustiloxin A, the main toxic component in V. virens. In addition to the two main transformed products previously identified, ustiloxins A1 and A2, an additional transformed product was obtained by using cell-free extract (CFE) of P. setifera Nitaf10 prepared with 5 mmol/L of pH 9.0 carbonate-buffered solution (CBS). It was structurally characterized as a novel ustiloxin analog named 13-hydroxy ustiloxin A (1) by analysis of the 1D and 2D NMR and HRESIMS spectra as well as by comparison with known ustiloxins. Biotransformation reaction of ustiloxin A was found to proceed via hydroxylation, and was possibly catalyzed by the intracellular hydroxylase in the CFE. The cytotoxic and phytotoxic activities of 13-hydroxy ustiloxin A (1) were much weaker than those of ustiloxin A. Detoxification of ustiloxin A by hydroxylation of P. setifera will be an efficient strategy.