The dichlorvos-ammonia (DV-AM) method followed by single colony AM assay was applied for re-screening of aflatoxigenic fungi from soil samples from sugarcane field in Okinawa, Japan. In previous study, we obtained two aflatoxigenic isolates of Aspergillus pseudonomius located in Aspergillus nomius clade from one of soil samples. In this study, we re-screened the same soil sample and found an isolate with different morphology and toxigenic profile. Molecular phylogenic analyses of the isolate indicated that it is a closely related species of A. novoparasiticus located in Aspergillus flavus clade. This is the first report of this species of Aspergilli in Japan. Thus, the DV-AM method with single colony AM assay can be used as a tool to elucidate the diversity of aflatoxigenic fungi colonizing in the field soil.
The production of trichothecene is dependent on the yeast extract brands and lots. Synthetic medium is more suitable for elucidating the regulatory mechanism of mycotoxin biosynthesis. The use of synthetic medium with a single amino acid or polyamine as the sole nitrogen source could lead to an erroneous conclusion about the role of catabolism-related genes on secondary metabolism. Here, we report the development of a culture system that helps analyze the nutritional and/or genetic factors associated with trichothecene biosynthesis. By optimizing the nitrogen source and the initial pH of the synthetic medium, the suppressive effect of L-Thr catabolism on trichothecene production was demonstrated in the shortened period of manual pH adjustments of the culture medium. This culture system with different nitrogen concentrations and initial pHs was also useful for demonstrating the indispensability of FgAreA in trichothecene biosynthesis.
Food and environmental exposure to trichothecenes, a group of mycotoxins produced by filamentous fungi such as Fusarium, Trichothecium, Trichoderma, and Myrothecium, threatens the health of humans and livestock. The toxins are conventionally classified into types A through D based on their characteristic chemical structures (e.g., the presence of C-8 ketone, 7,8-epoxide, or macrocyclic ring between C-4 and C-15). However, from the viewpoint of biosynthesis, it is more reasonable to classify them into two groups, C-3 unoxygenated d-type trichothecenes and C-3 oxygenated t-type trichothecenes, which are produced by the cyclization of isotrichodiol and isotrichotriol, respectively. Using molecular genetic approaches, we characterized the biosynthetic enzymes of several trichothecene-producing fungi and identified many natural and unnatural trichothecenes. Based on our achievements, an MS/MS library comprising various trichothecene intermediates is being constructed. We believe that in the near future, our MS/MS library will be useful for detecting the emergence of novel trichothecenes.
Mass spectrometry imaging (MSI) is a promising visualization technique for metabolite distribution analysis in agricultural products. Here, we introduce the workflow of the matrix-assisted laser desorption/ionization (MALDI)-MSI analysis, followed by our recent studies on strawberry fruit, pork meat, and immature Phaseolus vulgaris L. seed metabolites using MALDI-MSI. We anticipate that the use of MSI will further expand towards the analysis of various agricultural products.
The 2030 agenda for 17 Sustainable Development Goals (SDGs) was adopted by all United Nations member states in 2015. Some goals have close relation with research subjects in microbiology. In consideration of the connection to SDGs, we present the results of our recent research on degradation of biomass by filamentous fungi.
The occurrence of mould and yeast in food and related products is well documented. These fungi are known to cause food spoilage and mycotoxin contamination. This article introduces food-borne fungal tests for students and beginners.