Species composition and toxicological characteristics of fungi of the genus Aspergillus isolated from coarse fodders

The problem of ensuring the safety of coarse fodders, which annually replenishes the Russian feed production on a large scale, raises concern about the multiple combined contamination with mycotoxins and the extensive spread of toxigenic fungi. Recently, it has been established that F. sporotrichioides plays a dominant role among fusarium fungi in these fodders, producing metabolites, the T-2 toxin and diacetoxyscirpenol, which can cause acute poisoning in animals. The purpose of this work, which became the next stage in the study of the main toxin-producing micromycetes of coarse fodders, was the determination of the species composition, occurrence and toxin production in fungi of the genus Aspergillus under experimental conditions favourable for the fullest realization of their potential. The objects of mycological analysis were 258 average samples from the production batches of hay and straw harvested in the livestock farms of Bryansk (2011) and Moscow (2013) regions. Isolates with established species affiliation were cultivated on Czapek-Dox agar (CDA), wort agar (WA) and moistened rice grain (RG) for 7 days at 23 °C. The content of sterigmatocystin (STE), emodin (EMO), aflatoxin B1 (AB1), ochratoxin A (OA), mycophenolic acid (MPA), cyclopiazonic acid (CPA), ergot alkaloids (EA), deoxynivalenol (DON) and fumonisins (FUM) in extracts of mycelial spore biomass were determined by enzyme immunoassay with certified test systems. To assess the toxin production, 32 isolates of 12 species of Aspergillus fungi of hay and straw were used, as well as 27 isolates of A. flavus Link, A. pseudoglaucus Blochwitz, A. repens de Bary isolated earlier from grain fodders. Fungi of the genus Aspergillus were found in samples with a frequency of 62.0 % and an infection rate of 1.7-100 %. The obtained isolates belonged to 15 species included in 10 taxonomic groups with the largest species diversity in the A. glaucus group (4 species). The most common species were A. flavus and A. niger van Tieghem (more than 50.0 % of the contaminated samples), followed by A. versicolor (Vuill.) Tiraboschi, A. pseudoglaucus, A. amstelodami (Mangin) Thom & Church, A. ochraceus Wilhelm and A. wentii Vehmer (10.6-18.8 %), A. nidulans Eidam (6.3 %), the remaining 7 species - A. candidus Link, A. tamarii Kita, A. sydowii (Bain. & Sart.) Thom & Church, A. fumigatus Fresenius, A. repens, A. terreus Thom, A. chevalieri (Mangin) Thom & Church were less common (< 5 %). The intensity of formation of the CPA ( A. flavus ) and MPA ( A. pseudoglaucus, A. repens ) was quite comparable in the CDA and RG. Compared to WA, a greater accumulation of the majority of mycotoxins occurred in the RG, i.e. STE ( A. versicolor, A. nidulans ), CPA ( A. flavus, in all 5 A. tamarii isolates CPA could be detected only on this substrate) and EMO ( A. sydowii ). For the biosynthesis of MPA in A. pseudoglaucus and A. repens, WA was preferred. Testing of fungi on three nutrient media allowes us to establish that a complex of Aspergillus fungi which includes 7 species can be associated with the contamination of coarse fodders with STE, CPA and MPA; the source of EMO contamination among the fungi of the genus Aspergillus was not found. Only two of the three isolates of A. sydowii produced it in small amounts of 120±20 and 245±40 ng/g. The remaining mycotoxins analyzed in the isolates were not detected. The possibility of participation of fungi of other systematic groups in the contamination of fodder with STE, CPA, MPA and EMO is discussed, whereas clusters encoding the biosynthesis of mycotoxins have been found in micromycetes from genetically distinct groups in recent years.