Inhibitory Activities of Alkyl Syringates and Related Compounds on Aflatoxin Production

Mutual effects on mycotoxin production during co-culture of ochratoxigenic and aflatoxigenic Aspergillus strains

Mycotoxin co-occurrence compromises the safety of food crops worldwide. Environmental factors, as well as fungal interaction, can substantially influence the infectivity of mycotoxigenic fungi and their subsequent production of multi-mycotoxin. Here, we investigated the mutual effects of the co-culture of ochratoxigenic and aflatoxigenic Aspergillus strains on the co-production of ochratoxin A (OTA) and aflatoxin B1 (AFB1). Single cultures of ochratoxigenic A. carbonarius and A. alliaceus grew optimally at 25 °C, whereas aflatoxigenic A. flavus grew optimally at 35 °C. The maximum levels of OTA and AFB1 were achieved at 25 °C, whereas mycotoxin production decreased at 35 °C. During competitive growth of the ochratoxigenic and aflatoxigenic isolates, inhibition or stimulation of mycotoxin production was dependent on the fungal strain, temperature, and the ratio of the spore concentration. Aspergillus carbonarius and A. alliaceus generally produced OTA, with similar patterns of relative OTA levels at all temperatures. AFB1 production by A. flavus in the presence of ochratoxigenic Aspergillus species was inhibited at 25 °C and stimulated at 35 °C. These results indicated that the temperature, presence of other mycotoxigenic Aspergillus species, and ratio of the initial spore concentration significantly contributed to the co-production of OTA and AFB1.

Sabotage at the Powerhouse? Unraveling the Molecular Target of 2-Isopropylbenzaldehyde Thiosemicarbazone, a Specific Inhibitor of Aflatoxin Biosynthesis and Sclerotia Development in Aspergillus flavus, Using Yeast as a Model System

Amongst the various approaches to contain aflatoxin contamination of feed and food commodities, the use of inhibitors of fungal growth and/or toxin biosynthesis is showing great promise for the implementation or the replacement of conventional pesticide-based strategies. Several inhibition mechanisms were found taking place at different levels in the biology of the aflatoxin-producing fungal species such as Aspergillus flavus: compounds that influence aflatoxin production may block the biosynthetic pathway through the direct control of genes belonging to the aflatoxin gene cluster, or interfere with one or more of the several steps involved in the aflatoxin metabolism upstream. Recent findings pointed to mitochondrial functionality as one of the potential targets of some aflatoxin inhibitors. Additionally, we have recently reported that the effect of a compound belonging to the class of thiosemicarbazones might be related to the energy generation/carbon flow and redox homeostasis control by the fungal cell. Here, we report our investigation about a putative molecular target of the 3-isopropylbenzaldehyde thiosemicarbazone (mHtcum), using the yeast Saccharomyces cerevisiae as model system, to demonstrate how the compound can actually interfere with the mitochondrial respiratory chain.

The Mode of Action of Cyclo(l-Ala-l-Pro) in Inhibiting Aflatoxin Production of Aspergillus flavus

Cyclo(l-Ala-l-Pro) inhibits aflatoxin production in aflatoxigenic fungi without affecting fungal growth. The mode of action of cyclo(l-Ala-l-Pro) in inhibiting aflatoxin production of Aspergillus flavus was investigated. A glutathione S-transferase (GST) of the fungus, designated AfGST, was identified as a binding protein of cyclo(l-Ala-l-Pro) in an experiment performed using cyclo(l-Ala-l-Pro)-immobilized Sepharose beads. Cyclo(l-Ala-l-Pro) specifically bound to recombinant AfGST and inhibited its GST activity. Ethacrynic acid, a known GST inhibitor, inhibited the GST activity of recombinant AfGST and aflatoxin production of the fungus. Ethacrynic acid reduced the expression level of AflR, a key regulatory protein for aflatoxin production, similar to cyclo(l-Ala-l-Pro). These results suggest that cyclo(l-Ala-l-Pro) inhibits aflatoxin production by affecting GST function in A. flavus, and that AfGST inhibitors are possible candidates as selective aflatoxin production inhibitors.