Trichothecene-Producing Fusarium Species: Systematics & Biodiversity

none[Synopsis] Several species of the genus Fusarium produce trichothecene mycotoxins. We analyzed DNA sequence of a variable region at the 5' end of the large nuclear ribosomal DNA (rDNA) (28S) to determine the genetic relatedness of trichothecene-producing Fusarium species. All tricotheceneproducing atrains were clustered together, and divided into two monophiletic groups. The first Glade included strains of Fusarium that produce type A tricothecenes (T-2 toxin, HT-2 Toxin, neosolaniol, and diacetoxyscirpenol). The second Glade was consisted of strains of Fusarium species which produce type B tricothecenes (fusarenone-X, nivalenol, and deoxynivalenol). In this report we discuss a polyphasic approach to specify the biodiversity in F. camptoceras sensu lato, a member of the Arthrosporiella section of Fusarium genus, which have been considered as a saprophitic fungus and a secondary invader of plant tissues.By means of toxin analysis, biological assays, and molecular studies, three diffarent populations of F. camptoceras were recognaized, substanting previous re-classification of these three populations as new species on the basis of morphological traits. Toxigenic fungi are very common in nature and are able to produce a wide variety of active secondary metabolites. Under a continue evolutionary pressure for a better adaptation and colonization of different ecological systems, the fungi have modified many of their biological characteristics, including the biosinthetic metabolism. Some metabolites are toxic toward plants, insects and other microorganisms, playing an important role in the fungal pathogenesis and antagonism. Other toxic metabolites can be accumulated during a large colonization by toxigenic fungi in agricultural commodities and fodder, representing a high risk for animal and human health for the effects of contaminated feed and food consumption. From chemical point of view, the toxins are characterized by different structure (e.g. peptides, terpenes) to which may correspond a significant difference in their biological activity. In some case also small changes in the chemical structure of the toxins can correspond to a significatively different activity. In spite of their common or similar biosynthetic ability, some toxigenic fungi are placed taxonomically distant. The current classification system of toxigenic fungi is very limitative because still principally based on morphology (Hughes, 1953). On the other hand, phylogenetic studies can be useful, besides a strict taxonomic classification, also to better understand the evolutionary relationships among taxa, which can include informations on some physiological and biochemical fungal traits (e.g. enzymatic and secondary metabolite pathways). Recently, ribosomal RNA coding sequences have been often used to assess phylogenetic relationships among fungi. The advantages of using these sequences for phylogenetic studies is that this molecule is universally present in all living cells and that its sequence is not correlated with a particular morphology. It is known, however, that not all portions of the molecule are equally suitable for detecting molecular changes, as different portions of the molecule are subject to different selection pressures. The structural features shared by 28S-like molecules in all species provides a versatile and sensitive plylogenetic indicator, since highly conserved sequences are interspersed with much more rapidly evolving domains (Clark et al., 1984; Hassouna et al., 1984). In this report, we discuss the genetic relatedness of some toxins (trichothecenes) producing fungi, through sequence analysis of a variable region at the 5'end of the nuclear large subunit (LSU) ribosomal DNA (rDNA) (28S) and report an example of the biodiversity of trichothecene-producing Fusarium camptoceras sensu lato by some molecular and biochemical approaches