Low-dose ethanol increases aflatoxin production due to the adh1-dependent incorporation of ethanol into aflatoxin biosynthesis

Aflatoxins are toxic secondary metabolites produced by some aspergilli, including Aspergillus flavus. Recently, ethanol has attracted attention as an agent for the control of aflatoxin contamination. However, as aflatoxin biosynthesis utilizes acetyl coenzyme A, ethanol may be conversely exploited for aflatoxin production. Here, we demonstrated that not only the C-13 of labeled ethanol, but also that of labeled 2-propanol, was incorporated into aflatoxin B-1 and B-2, and that ethanol and 2-propanol upregulated aflatoxin production at low concentrations (<1% and <0.6%, respectively). In the alcohol dehydrogenase gene adh1 deletion mutant, the C-13 incorporation of labeled ethanol, but not labeled 2-propanol, into aflatoxin B-1 and B-2 was attenuated, indicating that the alcohols have different utilization pathways. Our results show that A. flavus utilizes ethanol and 2-propanol as carbon sources for aflatoxin biosynthesis and that adh1 indirectly controls aflatoxin production by balancing ethanol production and catabolism.

Automated summary

Recent studies have shown that ethanol can be utilized by Aspergillus flavus for aflatoxin production. This study further demonstrates that both labeled ethanol and labeled 2-propanol can be incorporated into aflatoxin B-1 and B-2, and that low concentrations of ethanol and 2-propanol can upregulate aflatoxin production. The alcohol dehydrogenase gene adh1 is found to regulate aflatoxin production by controlling ethanol production and catabolism.