Production of ochratoxin a, fumonisins and emodin by Aspergillus niger isolates from feed products

Micromycetes of one of the most complex taxonomically complex Aspergillus niger (the A. niger “aggregate”) in recent decades have invariably remained the object of close attention of researchers due to the risks of negative effects on humans and animals. For industrial and collection strains, the ability to synthesize toxic metabolites with particularly dangerous forms of action has been established - ochratoxin A (M.L. Abarca et al., 1994; J. Téren et al., 1996; J. Varga et al., 2002), group B fumonisins (J.C. Frisvad et al., 2007; J.M. Mogensen et al., 2010; M. Månsson et al., 2010) and emodin (A.A. Ismaiel et al. 2016). Strains producing ochratoxin A and fumonisins have been identified in food (P. Noomin et al., 2009; M. Storari et al., 2012; M. Yanai et al., 2013) and feed products (A. Dalcero et al., 2002; F. Accensi et al., 2004). In Russia, priority in the study of these fungi was given to assessing their danger as pathogens of mycoses in the human environment (A.B. Kulko, 2012; O.E. Marfenina et al., 2014). In this work, for the first time for A. niger from domestic grain feed products and storaged grass feeds (E.A. Piryazeva, L.S. Malinovskaya, 2013, 2014), the features of mycotoxin production was established, the influence of the type of substrate on the intensity of toxin formation in vitro was shown, and it was confirmed that it belongs to the species A. niger as part of A. niger “aggregate” (R.A. Samson et al., 2007). The purpose of the study was to assess the ability of A. niger cultures isolated from combined feed, five types of feed raw materials and hay of different botanical composition and territorial origin to produce B group fumonisins (FUM), ochratoxin A (OA), emodin (EMO), as well as to clarify their species according to the totality of morphological, physiological characteristics and composition of metabolites. For 12 monoconidial strains, toxin production was assessed on sucrose agar with yeast extract (YES), Czapek agar with yeast autolysate extract and 20% sucrose (CYA20S) and on rice grain. After incubation (7 days, 25ºC), the extracts were analyzed using test systems for enzyme-linked immunosorbent determination of mycotoxins (STO VNIIVSGE). According to morphological criteria (diameter of colonies, growth pattern, color, consistency of colonies, shape and width of the growing edge, shape of the conidial head, structure and pigmentation of conidiophores, size, shape and color of vesicles, metulae, phialids and conidia), according to the absence of sclerotia, results of Ehrlich test and the ability to produce OA and FUM, their belonging to the species A. niger in the clade of biseriate species was confirmed (R.A. Samson et al., 2007; J. Varga et al., 2011). The accumulation of FUM in 7 strains was 0.2 to 630 μg/g and absent in 5; all strains produced OA (from 0.005 to 0.064 μg/g) and EMO (from 0.004 to 0.9 μg/g). The difference in the accumulation of mycotoxins on agar media and grain substrate confirms the influence of substrate components on the activity of determinant gene clusters. Due to the weak potential for producing OA, EMO and the small proportion of active FUM producers, the contribution of A. niger to the contamination of grain feed and hay, even with intensive infestation, is unlikely to be significant.