Impact of OTAbZIP on Ochratoxin A production, mycelium growth and pathogenicity of Aspergillus westerdijkiae under water activity stress

Aspergillus westerdijkiae is a major producer of ochratoxin A (OTA), a highly toxic and carcinogenic mycotoxin found in various food and feed products. A. westerdijkiae produces excessive amount of OTA under various water activity (a_w) conditions that occur during food and feed storage. The biosynthetic gene clusters associated with OTA production include OTAbZIP, which plays a key role in controlling mycotoxin production in response to environmental conditions. This study explored the regulation of OTA biosynthesis in A. westerdijkiae fc-1, focusing on the OTAbZIP gene’s influence under a_w stress. The mycelium growth of A. westerdijkiae fc-1 wild type and OTAbZIP mutant strains increased by 40.7% and 50.5% under high water activity (0.96 a_w) respectively, at 6 days post-inoculation (dpi), indicating a stress on A. westerdijkiae fc-1. While OTAbZIP mutant did not produce OTA under both high and moderate a_W conditions. The wild type produced OTA and OTA biosynthetic gene expression levels were downregulated under high (0.96 a_w) and moderate (0.91 a_w) water activity. The expression level of hog1 gene in OTAbZIP mutant was significantly lower than in the wild type. Pathogenicity tests revealed that deletion of OTAbZIP did not significantly affect disease infection. This study shows that deleting OTAbZIP gene greatly reduces OTA production, affecting the strain’s adaptability to water activity stress.