Fusarium asiaticum was used to investigate factors affecting the regulation of deoxynivalenol (DON) production. In liquid medium supplemented with a low concentration of rapamycin, F. asiaticum grew at approximately 40% of its normal rate but did not produce DON. RNA levels were measured by next generation RNA sequencing. In low concentration rapamycin, expression levels of DON-related genes were low, but expression of the FaTor (target of rapamycin of F.asiaticum) gene was not suppressed. However, expression of the FaTap42 gene, which interacts with FaTor, was suppressed to nearly 70%. FaSit4 and FaPpg1 genes, which were downstream of FaTap42, were down regulated. However, expression of the FaPp2A gene, another phosphatase downstream of FaTap42, was not affected by low concentration rapamycin. These findings reveal that low concentration rapamycin differentially suppresses genes downstream of the FaTor pathway.
Eushearilide, a newly isolated macrolide antibiotic isolated from Eupenicillium shearii, has been examined for its toxic effects on mitochondrial respiration and structure to gain insight into the molecular mechanism for the antifungal activity, by using freshly isolated rat liver mitochondria. Eushearilide inhibited the respiration oxidizing both L-glutamate and succinate. The inhibition was not reversed by N,N,N',N'-tetramethyl-1,4-phenylenediamine dihydrochloride, which generates an electron transport shunt over the inhibition sites of rotenone and antimycin A, and was not restored by ascorbate, an artificial substrate for the cytochrome c oxidase. The all of cytochromes a, b and c were kept reduced in the presence of eushearilide in the reducedminus oxidized difference spectrum of cytochromes. Eushearilide induced a large amplitude swelling in the mitochondria suspended in an isotonic KCl solution. This amplitude swelling was prevented by cyclosporine A, indicating the generation of the permeability pore in the inner membrane. These results suggested that eushearilide could impair mitochondrial respiratory function by inhibiting the electron transport at the site of complex IV (cytochrome c oxidase) in the respiratory chain and by inducing swelling.
Blasticidin A, a Streptomyces metabolite, inhibits aflatoxin production in aflatoxigenic fungi. The mode of action of blasticidin A in the inhibition of aflatoxin production was investigated. Blasticidin A inhibited human PTP1B (a protein tyrosine phosphatase) with the IC50 value of 27 μM, but not human PP1A (a protein serine/threonine phosphatase). Dephostatin, a known protein tyrosine phosphatase inhibitor, inhibited aflatoxin production without affecting fungal growth. Blasticidin A delayed expression of aflR, which encodes the key regulator of aflatoxin production, and aflatoxin biosynthetic enzyme genes, whereas dephostatin did not affect their mRNA levels. Aspergillus flavus has two genes encoding PTP1B homologs, AfPTP1B-1 and AfPTP1B-2. Blasticidin A inhibited recombinant AfPTP1B-1 more strongly than did dephostatin, and dephostatin inhibited recombinant AfPTP1B-2 much more strongly than did blasticidin A. These results suggest that aflatoxin production is regulated by some protein tyrosine phosphatases, and that protein tyrosine phosphatase inhibitors are potential aflatoxin production inhibitors.
The study to evaluate the effects of isothiocyanate compounds (ITCs) on the production of aflatoxin B1 (AFB1) by an aflatoxigenic fungus was conducted. Allyl isothiocyanate (AITC) and methyl isothiocyanate (MITC) were tested for the inhibitory effects on the growth and AFB1 production of an Aspergillus flavus strain. ITCs diluted with dimethyl sulfoxide were administered in a liquid medium containing spores of A. flavus in triplicates. Adding ITCs decreased concentration of AFB1 in medium after cultivation in a dose-dependent manner. These effects were more potent than those caused by caffeine, one of the well-known inhibitors of AFs production. Furthermore, among two ITCs, MITC was more potent than AITC. It is well-known that ITCs are included in certain family of Brassicaceae and Cleomaceae as natural volatiles, respectively. Thus, they may become one of new tools to control AFs by plants.
Fusarium head blight (FHB) is inevitable because climate in Japan is warm and humid, and wheat and barley grains are contaminated with mycotoxins such as deoxynivalenol (DON) which are produced by pathogen of FHB. For the Ministry of Agriculture, Forestry and Fisheries (MAFF) responsible for the stable supply of safe and quality food, risk management on mycotoxins in wheat and barley is an important issue. MAFF has established guidelines which recommend pathogen control in optimum timing with effective pesticides, harvesting in proper time, thorough drying and sorting, etc., for reduction of mycotoxin contamination in wheat and barley during the production stage and is promoting implementation of the guidelines.
The results of surveillance on mycotoxins in domestic wheat and barley showed that there is a remarkable annual variation of DON concentration in grains according to the outbreak of FHB and that health risk of preschool children from DON exposure is not negligible. As there is a possibility that the occurrence of FHB may increase result from the effect of climate change, etc., it is necessary to take continual surveillance and thorough reduction measures.
The 3rd International Conference of Mycotoxicology and Food Security (ICM 2019) organized by Association of Mycotoxicology (Thailand) was held from February 6th to 7th, 2019, at Bangkok, Thailand. The overview of the conference is reported.