The bZIP transcription factor Afap1 mediates the oxidative stress response and aflatoxin biosynthesis in Aspergillus flavus

Aflatoxin is a carcinogenic secondary metabolite produced mainly by Aspergillus flavus and Aspergillus parasiticus, which can seriously endanger the health of humans and animals. Oxidative stress is a common defense response, and it is known that reactive oxygen species (ROS) can induce the synthesis of a series of secondary metabolites, including aflatoxin. By using mutants lacking the afap 1 gene, the role of afap 1 gene in oxidative stress and aflatoxin synthesis was assessed. The growth of the mutant strains was significantly inhibited by the increase in the concentration of H2O2, inhibition was complete at 40 mmol/l. However, in the quantitative analysis by HPLC, the concentration of AFB(1) increased with the increased H2O2 until 10 mmol/l. Following an analysis based on the information provided by the NCBI BLAST analysis, it was assumed that Afap1, a basic leucine zipper (bZIP) transcription factor, was associated with the oxidative stress in this fungus. Treatment with 5 mmol/l H2O2 completely inhibited the growth of the mutant strains in afap 1 but did not affect the growth of the CA14PTs strain (non-mutant strain). In addition, the concentration of AFB 1 in the mutant strains was approximately 1/4 of that observed in the CA14PTs strain. These results suggested that Afap1 plays a key role in the regulation of oxidative stress and aflatoxin production in A. flavus. (C) 2018 Published by Elsevier Espana, S.L.U. on behalf of Asociacion Argentina de Microbiologia.