Biosynthetic studies of fumonisin B1 and AAL toxins

The biosynthesis of the sphinganine analogue mycotoxins (SAMs) fumonisin B-1 and the AAL toxins was studied by growing Fusarium moniliforme and Alternaria alternata f. sp. lycopersici in liquid culture. Radioactive and stable isotopically labeled amino acid, water, and molecular oxygen precursors were added to the culture media and toxins were analyzed using thin-layer chromatography, liquid scintillation counting, high-performance liquid chromatography (HPLC), C-13 nuclear magnetic resonance (NMR) spectroscopy, and electrospray mass spectrometry (ESMS). Results indicated that glycine was incorporated directly into the AAL toxins and that methionine was incorporated into the AAL toxin methyl groups. Oxygens in tricarballylic acid moieties for fumonisin B1 and the AAL toxins were derived from H2O while the lipid backbone hydroxyls for fumonisin BL and the AAL toxins originated from molecular oxygen. Isotopic enrichment patterns for the various AAL toxins showed marked differences among toxins, suggesting a complex, rather than sequential, biosynthetic pattern.