BIOSYNTHESIS OF FUSARIC ACID IN CULTURES OF FUSARIUM OXYSPORUM SCHLECHT

Abstract

The incorporation of radioactivity into fusaric acid from14C-labeled acetate and DL-aspartate was examined using two strains of Fusarium oxysporum. Acetate-1-14C labeled the carboxyl (C-7) group and alternate carbon atoms C-8 and C-10 of the n-butyl chain. The remaining two carbon atoms (C-9 and C-11) of the n-butyl chain were labeled by acetate-2-14C, which contributed only a small amount of radioactivity to C-7. Both precursors labeled the pyridine ring. Almost two-thirds of the label in fusaric acid produced from DL-aspartate-1-14C was in C-7 with most of the remainder in the pyridine ring; DL-aspartate-4-14C gave the reverse pattern. The proportion of radioactivity in C-7 decreased only slightly when contact time between precursor and culture was reduced. The distribution of label between C-7 and the pyridine ring was similar to that between C-1 and C-4 of protein aspartic acid isolated in the same experiment. Malonate-2-14C and glycerol-1,3-14C labeled fusaric acid to approximately the same extent as DL-aspartate-4-14C, but succinate-1,4-I4C was a poor precursor. The results are consistent with the biogenesis of fusaric acid from three units of acetate and one of aspartate. Yields of the metabolite from cultures grown on a modified Richards' medium were increased by supplements of sodium acetate, but not of aspartate.