This study investigated whether kojic acid is an intermediate in aflatoxin biosynthesis by Aspergillus flavus using resting cells. The researchers tested various carbon substrates, environmental conditions, and radioactively labeled compounds to determine if the two metabolites share a common biosynthetic pathway. Results showed that glucose was the optimal substrate for aflatoxin production, while D-xylose and ethanol preferentially supported kojic acid formation. The two compounds responded differently to changes in pH, temperature, and surface-area-to-volume ratios. Isotopic labeling experiments proved crucial: when [14C]acetate was provided, aflatoxin incorporated substantial radioactivity, but adding unlabeled kojic acid did not reduce this incorporation. Conversely, when [14C]kojic acid was the labeled substrate, aflatoxin formation was minimal, and supplementing with unlabeled acetate significantly reduced the toxin's specific activity. These data conclusively demonstrate that kojic acid and aflatoxin synthesis follow separate metabolic pathways controlled by different enzyme systems, and that kojic acid is not an intermediate in aflatoxin biosynthesis by resting A. flavus cells.

Key findings

• Glucose yielded the highest aflatoxin production by resting A. flavus cells, while D-xylose and ethanol preferentially promoted kojic acid synthesis
• Aflatoxin and kojic acid synthesis responded differently to pH, temperature, and surface-area-to-volume ratio changes, indicating separate regulatory mechanisms
• Isotopic labeling with [14C]acetate showed strong aflatoxin incorporation unaffected by unlabeled kojic acid addition, proving kojic acid is not an intermediate
• Labeling experiments with [14C]kojic acid produced minimal aflatoxin formation, further confirming separate biosynthetic pathways
• Different chemical treatments (dithionite, malonate, nitrogen atmosphere) selectively affected kojic acid or aflatoxin production but not both