Mycotoxins - Their Biosynthesis in Fungi: Zearalenone Biosynthesis ¹

Zearalenone [6-(10-hydroxy-6-oxo-trans-1-undecenyl)-β-resorcylic acid lactone] is biosynthesized by Fusarium roseum by head-to-tail condensation of acetate units via the acetate-malonyl-CoA (polyketide) pathway. Incorporation and distribution of 1-[¹⁴C]acetate into zearalenone was demonstrated by degradation of the molecule into the aromatic ring, CO₂, oxalic, succinic and glutaric acids. Incorporation and distribution of 1-[¹³C]acetate and 1,2-[¹³C]acetate was demonstrated by ¹³C-NMR and confirmed the conclusion reached by ¹⁴C-incorporation studies. CO₂ is rapidly fixed by cultures of F. roseum , presumably by phosphoenolpyruvate carboxykinase and pyruvate carboxylase and incorporated into zearalenone. The wild-type isolates of F. roseum normally produce optimum amounts of zearalenone on a solid medium such as rice and at lower temperatures (10-14 C), although mutants are available that produce copious amounts in liquid medium. Some wild-type isolates also produce zearalenone optimally at 20-25 C.