Phylogenetic relationships of important trichothecene-producing strains originally identified as Fusarium nivale Fn-2, Fn-3 and Fn-2B and F. episphaeria Fn-M were investigated within the Gibberella lineage of Fusarium using nucleotide characters obtained by sequencing polymerase chain reaction (PCR) DNA amplified from the following 4 loci: nuclear 28S ribosomal DNA, nuclear ribosomal internal transcribed spacer (ITS) region, mitochondrial small subunit (mtSSU) ribosomal DNA, and β-tubulin gene exons and introns. Parsimony analysis of the individual and combined data sets indicate that Fn-2, Fn-3, Fn-2B, and Fn-M represent an undescribed species of Fusarium. Bootstrap and decay analysis identified a clade containing F. sambucinum and several other diacetoxyscipenol (DAS) and/or T-2 trichothecene-producing species as a sister to Fusarium sp. n. The outgroup species used to root the tree, by contrast, produce a different set of mycotoxins that include deoxynivalenol and zearalenone. These results emphasize the importance of investigating the evolution of Fusarium toxins the contex of a robust species-level phylogeny.
As a new toxic fungal metabolite, nivalenol (NIV) was found from the rice culture of Fusarium species Fn-2B strain by Tatsuno et al. in 1968. This fungus was originally identified as F. nivale and the metabolite was named from the species. NIV, one of the 8-ketotrichothecenes (type B), occurs worldwide and possesses cytotoxicity to mammalian cells and tissues.
The production of trichothecene mycotoxins in Fusarium sp. Fn 2 (NRRL 3509), originally identified as F. nivale was reexamined in details. Shake flask cultures with peptone-sucrose-yeast extract medium produced fusarenon-X (FX=4-acetyl-nivalenol) and diacetoxyscirpenol (DAS) as major products, along with other trichothecenes as minor products, including some tentatively identified as 9-hydroxy-trichotriol, sambucoin, 13-hydroxy-11-epi-apotrichothecene, verrucarol and FS-1. In rice cultures, the major metabolites found were nivalenol (NIV) and FX. Of these toxins, DAS has the highest toxicity towards mammalian cells followed by FX and NIV. The present data revealed that strain Fn 2B produces both the type A (DAS) and type B (NIV/FX) trichothecenes, as observed in F. poae.
It has been reported that T-2 toxin, a trichothecene mycotoxin produced by Fusarium species, induces cellular destruction in bone marrow and thymus cells, followed by reduced numbers of peripheral white blood cells, and this mycotoxin evokes apoptotic cell death in human peripheral blood lymphocytes (hPBLs). To clarify a possibility that the affects of nivalenol (NIV), a trichothecene mycotoxin produced by Fusarium species, on peripheral blood cells cause reduction in the number of peripheral blood cells, we analyzed nivalenol-induced apoptosis in hPBLs in vitro and mouse PBLs (mPBLs) in vivo using flow cytometer. NIV induced apoptosis in hPBLs time-and dose-dependently, while 1, 2-Bis (o-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid tetra (acetoxymethyl) ester (BAPTA-AM), an intracellular Ca++ (Ca++1) chelator, efficiently inhibited the apoptotic cell death just like T-2 toxin-induced apoptosis.
Following our previous studies, the comparative study on the natural occurrence of mycotoxins in staple foods from the high- and low-risk areas for human esophageal cancer (HEC) in China was carried out. A total of 54 corn and 40 wheat samples intended for human consumption were collected from Linxian and Shangqiu Counties in Henan Province, high- and low-risk areas of HEC, respectively, and analyzed for fumonisins (FMs), trichothecenes (TRICs) and zearalenone (ZEA). Incidences of TRICs and ZEA in corn samples from the high-risk area were 3.7 and 11 times higher, respectively, than those in corn from the low-risk area. The levels of deoxynivalenol (DON), 15-acetyl-DON, nivalenol (NIV) and ZEA in corn, as well as those of DON and NIV in wheat, were all significantly higher in the high-risk area than those in the low-risk area. The high positive rate (79%) of FMs in corn from the high-risk area was found as compared with that (50%) in corn from the low-risk area, although no significant difference of FM levels was observed between the two areas. The results confirmed our previous reports : the contamination levels of TRICs and ZEA were positively correlated with the incidence of HEC, but FM levels were insignificantly different between the two areas.
Maize samples collected from fields, farm storages, middleman storages and food shops in Vietnam from May 1995 to August 1996 were analyzed for aflatoxin B1. The aflatoxin B1 productivity of Aspergillus flavus and Aspergillus payasitisus strains isolated from maize in North of Vietnam was also shown. The highest average levels of aflatoxin B1 was 130 ppb in maize kernel of Thanh Hoa-Nghe An province. One out of 10 of ear type samples from Ha Tay and two out of 10 of those from Thanh Hoa were contaminated at the level of 20 ppb and 60 ppb of aflatoxin, respectively. No aflatoxin was detected in maize based products. Twenty samples of maize kernel from provinces Ha Tay, Thanh Hoa, Son la in the North of Vietnam were collected for ochratoxin A analysis. Only one out of 20 samples was contaminated with ochratoxin A at the level of 90 ppb.
A simple and rapid analytical method has been developed for the determination of trichothecin (TCN) in agricultural products by gas chromatography (GC) equipped with an electron capture detector (ECD). TCN was extracted from them with aqueous acetonitrile and purified by a two-step chromatographic procedure using C18 cartridge and gel permeation chromatography (GPC) columns, quantified by capillary GC-ECD. The recoveries of TCN spiked to agricultural products were above 80%. The minimum detectable concentration of TCN was 0.1 μg/g.