Leucine auxotrophy specifically alters the pattern of trichothecene production in a T-2 toxin-producing strain of Fusarium sporotrichioides

Abstract

The biosynthetic pathway for trichothecenes in the filamentous fungus Fusarium sporotrichioides NRRL 3299 has been further characterized. Experiments using the techniques of mutational analysis and the incorporation of radiolabeled precursors indicated that leucine is a direct precursor to the isovalerate moiety present in the trichothecene, T-2 toxin. Analysis of trichothecene production in a UV-induced leucine auxotroph also revealed the existence of a branched biosynthetic pathway which results in the coproduction of T-2 toxin and the T-2 toxin analogs neosolaniol, 8-isobutyryl-neosolaniol, and 8-propionyl-neosolaniol. Leucine limitation imposed by the leucine auxotroph simultaneously led to underproduction of T-2 toxin and overproduction of these T-2 toxin analogs, which are produced in small amounts by the wild-type parent. Furthermore, it was shown that the ratio of T-2 toxin to T-2 toxin analogs produced by the leucine auxotroph can be modulated by the concentration of leucine in the medium. These results suggest that the four trichothecenes mentioned above are derived from a common intermediate and that there is competition for this intermediate among the branched pathways leading to these four cometabolites.