الفهرس 
TrichothecncesOnly 14 pages are availabe for public view
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Abstract
Trichothecene mycotoxins are nearly 190 closely related chemical compounds in the group of trichothecene toxins, named after the first isolated trichothecene molecule trichothecin. The basic structure of these molecules is tetracyclic, with a sesquiterpenoid 12, 13-epoxytrichothec-9-enering system. They are divided into four types (A, B, C and D), depending on the presence (macrocyclic trichothecenes) or absence (non-macrocyclic trichothecenes) of macrocyclic ring between C-4 and C-15, and further according to the number of hydroxyl and acetoxy groups attached to a carbon atom.. T-2 toxin was first isolated from the mould F. tricinctum (F. sporotrichoides). It belongs to nonmacrocyclic type A trichothecenes. It is produced primarily by Fusarium species such as F. acuminatum, F. nivale, F. oxysporum, F. poae, F. sporotrichioides, and F. solani. Dilution plate technique and direct culture methods were used to isolate Fusarium species from contaminated cereals grains and their products (barely, starch, wheat, flour and corn flour) at different regions of Egypt including Delta and Cairo governorate. Fusarium species were identified based on morphological features (macroscopic and microscopic features). Eighteen (18) strains of Fusarium were isolated and identified including (4) isolates of F. oxysporum , (3) isolates of F. solani, (2) isolates of F. equiseti, F. fujikuroi and F. brachygibbosum and (1) isolate of each of F. verticillioides , F. sporotrichioides, F. subglutinans, F. anthophylum and F. chlamydosporum. Eight strains out of eighteen (8/18) were easily identified by morphological and microscopic tools. These are F. equiseti (one isolate), F. oxysporum (four isolates), F. subglutinans (one isolate), F. anthophylum (one isolate) and F. brachygibbosum (one isolate). In addition, they showed negative results to produce toxins as revealed by TLC screening. Each Fusarium strain has different morphological colour varied from whitish to yellow, pink, red or purple shades in forward and reverase plate. Species of Fusarium typically produce both macro and microconidia from slender phialides. Morphological identification failed to distinguish between two F. solani strains. These two strains were identified clearly by molecular techniques. In addition, two strains (F. monilliformin and F. chlamydosporum) were identified by morphological tools. However, molecular techniques identified them as F. fujikuroi and F. verticillioides. In the present study, morphological and microscopic investigations were not able to identify F. sporotrichioides, while molecular technique using ITS rDNA region was able to identify it. Seven strains out of eighteen (7/18) were selected and identified with molecular technique (ITS rDNA), due to their activity in producing Fusarium toxin. Molecular identification based on ITS the total size of the ITS1 and ITS4 regions, including the 5.8S rDNA gene of the selected isolates varied from 500 to 650 bp. Fusarium sequences obtained from amplification of conserved ribosomal ITS region were compared with sequences from National Center for Biotechnology Information (NCBI) database using BLAST 2.0 (http://www.ncbi.nlm.nih.gov/ BLAST). These sequences were identified and deposited in NCBI GenBank with accession numbers. F. chlamydosporum was identified as F. fujikuroi (MG211161) with similarity percentage 98% to F. fujikuroi (HF679024.1). F. verticillioides was identified as F. fujikuroi (MG211162) with similarity percentage 98% to F. fujikuroi (MF510817). F. moniliformie was identified as F. verticillioides (XM 018895258.1) with similarity percentage 98%. Fusarium sp. was identified as F. sporotrichioides (MG211163) with similarity percentage 98% to F. sporotrichioides (EU520119.1). Fusarium sp. was identified as F. solani (MG211159) with similarity percentage 82% to F. solani (EU326459) and F. solani was identified as F. solani (MG211160). In the present study, genetic diversity within selected Fusarium species was studied. Dendrogram indicated that F. solani (MG211159) and F. verticillioides (XM_018895258.1) were grouped in one cluster. While, each of the other Fusarium species: F. fujikuroi (MG211162), F. sporotrichioides (MG211163), F. solani (MG211160) and F. equiseti (KM246255.1) were clustered in separate groups. Results of the present study indicated that induction media e.g pH, incubation temperature and composition have dramatic effects on toxin production by Fusarium species. TLC and HPTLC analyses of T-2 toxin were performed using a mobile phase (chloroform: ethyl acetate, 95:5) and produced good resolution. After extraction of the filtrate, colour varied from strain to another. When filtrate has dried, crystal shape appears in the baker as white needle crystals. The ability of Fusarium species to produce trichothecenes was investigated by TLC. Ten/eighteen Fusarium species were positive for production of trichothecenes such as T-2 toxin. F. fujikuroi (MG211162), F. equiesti (2 isolates), F. oxysporum, F. fujikuroi (MG211161), F. subglatinamy, F. anthophylum, F. solani (MG211159), F. verticillioides (XM- 018895258.1) and F. sporotrichioides (MG211163) were positive for T-2 toxin production with the Rf 0.25. HPTLC analysis confirmed only five strains of TLC results. HPTLC standard showed Rf 0.93 and quantified by detector UV/ Vis scanner. The results indicated 97% identity for F. fujikuroi (MG211162) and 98% identity for F. fujikuroi (MG211161) and F. verticillioides (XM_018895258.1). F. sporotrichioides (MG211163) showed 93% identity, while, F. solani (MG211159) indicated 95% identity. The present results demonstrated that HPTLC with densitometry, after a simple extraction procedure, can quantitate 76.5 μg/100 ml for F. fujikuroi (MG211159) with 98% identity. Lowest concentration 10.8 μg/100ml was obtained from F. verticillioides (XM_018895258.1) with 98% identity.