Masakatsu Ichinoe

Fungal melanin inhibitor and related compounds from Penicillium decumbens

Two polyketides, decumbenones A and B, and versiol were isolated from the culture filtrate of the fungus, Penicillium decumbens. Their respective structures were 1-(2,8-dihydroxy-1,2,6-trimethyl-1,2,6,7,8,8a-hexahydronaphthalen-1-yl)-3-hydroxy-1-propanone and 1-(2,8-dihydroxy-1,2,6-trimethyl-1,2,4a,5,6,7,8,8a-octahydronaphthalen-1-yl)-3-hydroxy-1-propanone based on NMR spectroscopic data, chemical conversion, and X-ray analysis. Decumbenone A inhibited melanization in Magnaporthe grisea, the rice blast pathogen, whereas decumbenone B like versiol did not.

Distribution of aflatoxin-producing Aspergillus flavus and Aspergillus parasiticus in sugarcane fields in the southernmost islands of Japan.

The distribution of Aspergillus flavus and Aspergillus parasiticus in sugarcane field soils and on harvested sugarcane stems was studied on seven islands of Okinawa and Kagoshima Prefectures, the southernmost prefectures in Japan. With the use of a combination of dilution plate and plant debris plate techniques, the fungi were detected on all seven islands studied and in 74% of 53 soil samples. The fungi were also found on the cut surfaces of sugarcane stems from one of the islands. A. parasiticus was the predominant fungus, although many atypical A. parasiticus isolates that produced metulated conidial heads were also obtained. The proportions of isolates testing positive for aflatoxin production were ca. 89% (146 of 164) of all isolates and ca. 69% of A. flavus isolates. More than 40% of A. flavus isolates also produced G aflatoxins. Scanning electron microscopic observation of conidial wall texture was useful in distinguishing A. parasiticus from A. flavus. Cyclopiazonic acid, an indole mycotoxin, was never synthesized by any of the A. parasiticus or G aflatoxin-producing A. flavus isolates tested.

Sorokinianin: A novel phytotoxin produced by the phytopathogenic fungus Bipolaris sorokiniana

Abstract Structure of sorokinianin, a novel phytotoxin from an isolate of Bipolaris sorokiniana was determined to be 3-hydroxy-5-(8′-hydroxymethyl-4′-isopropyl-1′-methyl-7′-methylenebicyclo[3.2.1]oct-6′-yl)tetrahydro-2-furanone predominantly on the basis of 2D NMR. The preliminary incorporation study suggested that this phytotoxin is derived biogenetically not from a geranylgeranylpyrophosphate through removal of two carbons but from a farnesylpyrophosphate and an additional C 3 unit.

Biosynthesis of sorokinianin a phytotoxin of Bipolaris sorokiniana: Evidence of mixed origin from the sesquiterpene and TCA pathways

Abstract Incorporation of sodium [1,2- 13 C 2 ]acetate confirmed that sorokinianin is, except for the C 3 portion, a sesquiterpene and indicated that the C 3 portion is derived from the acetyl CoA-related metabolic pathway. Results of replacement culture experiments suggested that the precursor of sorokinianin is prehelminthosporol, a major metabolite of B. sorokiniana OB-25-1, and a TCA cycle intermediate. Incorporation of [2,3- 13 C 2 ]succinic acid confirmed that the origin of the C 3 portion is a TCA cycle intermediate.

Phytotoxins and related metabolites produced by Bipolaris coicis, the pathogen of job's tears

Abstract Four metabolites were isolated and characterized from the phytopathogenic fungus Bipolaris coicis H-13-3. Radicinin and its diastereomer were phytotoxic against Jobs tears ( Coix lachryma-jobi ), a host of this fungus, but a diastereomer of radicinol and its epoxide were not phytotoxic.

Fusarium crookwellense, a newly isolated fungus from wheat in Japan: Its mycotoxin production and pathogenicity to wheat and barley

Fusarium crookwellense was isolated for the first time in Japan from scabby wheat harvested in Hokkaido in 1991. Four isolates were obtained and examined for their mycological features on culture media, mycotoxin production, and pathogenicity to wheat and barley. The texture of fungal colonies and the morphology of macroconidia on a potato dextrose agar medium were similar to those ofFusarium graminearum. AllF. crookwellense isolates examined produced nivalenol, 4-acetylnivalenol, and zearalenone on rice media at levels ranging from 0.9 to 22.5 µg/g, 0.5 to 25.0 µg/g, and 1.4 to 162.5 µg/g, respectively. All were pathogenic toward the wheat and barley strains tested, and scab symptoms were found on the heads and leaves of plants. This is the first report on domestic isolates ofF. crookwellense from the crop field in Japan.

Trends of fumonisin contamination and animal intoxication through monitoring 1991 to 1997 corn crop in the State of Paraná, Brazil.

Eleven feed samples associated with six animal (horse and poultry) intoxication outbreaks (1991) in the state of Paraná, Brazil, were evaluated for fungal and fumonisin contamination. In order to estimate the␣trend of livestock intoxication, fumonisin contamination was monitored in corn produced both at the commercial level (1991, 1995 crop), and in an experimental field at a local Agronomy Institute (1997 crop). The total mould count in the feed samples ranged from 2.9 × 103 to 1.9 × 107 CFU/g, with Fusarium verticillioides as the predominant species, at a high count of 2.4 × 104–6.5 × 105 CFU/g. Fumonisins (FB1 + FB2) were detected in all corn-based feed samples at levels ranging from 2.89 to 14.54 μg/g. All 27 Northern corn samples (1991 crop) were contaminated with fumonisins at levels ranging from 2.32 to 16.64 μg/g. Twenty-six (96.3%) out of 27 corn samples from the Central-Southern region (1995 crop) were positive for fumonisins (FB1+FB2), with the range of 0.07–3.66 μg/g, while all 37 Northern samples (1995 crop) were contaminated with fumonisins ranging from 0.57 to 9.97 μg/g. Twenty-one out of 37 corn samples from the Northern region (1997 crop) were positive for fumonisins, but at low level (range of 0.05–2.67 μg/g). The results showed a decreasing trend in fumonisin contamination over the years. Nowadays animal intoxication outbreaks rarely occur in this State, as both animal producers and feed industries have become conscious about monitoring of corn and other raw materials at the quality control level.

Inhibition of aflatoxin production and fungal growth on stored corn by allyl isothiocyanate vapor

Studies were conducted to determine the effectiveness of allyl isothiocyanate (AIT) vapor treatment with a commercial mustard seed extract (Wasaouro(®)) in controlling aflatoxin-producing fungi on stored corn. The concentration of AIT in the closed container peaked at 54.6 ng/mL on the 14th day and remained at 21.8 ng/mL on the 42nd day. AIT inhibited visible growth of aflatoxigenic molds in unsterilized corn and in sterilized corn inoculated with various aflatoxigenic fungi. However, fungi such as Aspergillus glaucus group, A. penicillioides and A. restrictus were detected by means of culture methods.

Formation Ratios of Zearalanone, Zearalenols, and Zearalanols versus Zearalenone during Incubation of Fusarium semitectum on Sorghum and Ratios in Naturally Contaminated Sorghum.

We incubated Fusarium semitectum on sorghum and measured the production of zearalenone (ZEN) and ZEN-related compounds (zearalanone (ZAN), α-zearalenol (α-ZEL), β-zearalenol (β-ZEL), α-zearalanol (α-ZAL) and β-zearalanol (β-ZAL)) in the culture by LC-MS. Of the five ZEN-related compounds, ZAN and β-ZEL were mainly detected. The concentrations of ZEN and the five ZEN-related compounds increased until 9 days after incubation and then increased slightly or stayed constant between days 9 and 15. The ratios of α-ZEL, β-ZEL, α-ZAL and β-ZAL to ZEN decreased in a similar manner after 7 days, whereas the ratio of ZAN to ZEN remained constant after 5 days. Analysis of naturally contaminated sorghum by LC-MS/MS revealed that the production ratio of α-ZEL to ZEN was inconsistent with that of our in vitro incubation analysis. The results indicate that ZAN might not be suitable for use as an internal standard.

Inhibition of Growth of Seed-Borne Fungi and Aflatoxin Production on Stored Peanuts by Allyl Isothiocyanate Vapor

Aspergillus parasiticus contamination of peanuts results in the production of highly toxic metabolites, such as aflatoxin B1, B2, G1 and G2, and its incidence in imported peanuts is reported to be increasing. Here, we examined whether the antifungal compound allyl isothiocyanate (AIT), which is present in mustard seed, could inhibit the growth of seed-borne fungi and aflatoxin-producing fungi. Peanuts produced in China and Japan were inoculated with A. parasiticus and exposed to AIT vapor released by a commercial mustard seed extract in closed containers under controlled conditions of temperature and humidity. AIT in the inoculated peanut samples reached its highest concentration of 44.8 ng/mL at 3 hr and decreased to 5.6 ng/mL after 9 weeks. Although AIT decreased the growth of the seed-borne fungi during the test period, the inoculated fungi survived. All tested peanuts samples were analyzed for aflatoxin using the HPLC method. There was a correlation between the number of aflatoxin-producing fungi and the total amount of aflatoxin production in the inoculated peanut samples. Our results indicate that AIT was effective in inhibiting the growth of seed-borne fungi and aflatoxin-producing fungi.