BIOSYNTHESIS OF NICOTINIC ACID BY FUSARIUM OXYSPORUM SCHLECHT
When the fungus Fusarium oxysporum was cultured on a glucose–nitrate–salts medium, synthesis of nicotinic acid occurred only during the early growth phase and preceded the accumulation of fusaric acid. Radioactivity from DL-tryptophan-benzene ring-14C was efficiently incorporated into nicotinic acid obtained by acid hydrolysis of the mycelium, whereas DL-tryptophan-β-14C, L-aspartate-U-14C, and sodium acetate-2-14C were poor precursors. Under the conditions of these experiments, all four substrates were poor precursors of fusaric acid. It is concluded that different pathways are used in the biosynthesis of these two pyridine derivatives, the route to nicotinic acid probably involving metabolism of tryptophan via the reactions known to occur in Neurospora crassa.