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  • Author or Editor: Tünde Pusztahelyi x
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Climate changes in Europe, which is characterized by the decrease of rainy days and the higher average temperature at summer, significantly increase the spreading of Aspergillus species and aflatoxin B1 contamination of the staple food and feed materials. The aim of our study was to estimate the possibility of the aflatoxin production of the Aspergilli on crops. From the isolates that were gained from crop samples, higher than 40% of the Aspergillus isolates contained norA, aflR and omtA genes from the aflatoxin genes cluster. Most of these isolates (63%) showed high homology with A. flavus, while three isolates showed high homology to A. tritici/A. candidus, one to A. cristatus/A. amstelodami and one strain showed the highest homology to A. tritici. Six from the A. flavus isolates (85.7%) with norA, aflR and omtA genes could produce aflatoxin B1 on malate extract agar medium. Parallel PCR and toxin measurements are recommended to evaluate the potentiality of aflatoxin production.

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Cornmeal agar (CMA) is a good to model natural conditions (low C and N, high antioxidants, crude fat) for phytopathogenic fungi. Different CMA media was prepared to model the maize kernel as growth environment for Aspergillus flavus, where stress resistance and aflatoxin B1 (AFB1) production were tested. The CMA medium with high polyphenol and low fatty acid content did not support the mycelial growth and high AFB1 production but the sclerotia development of the cultures. High fatty acid content in the CMA exceeded the inhibitory effect of antioxidant polyphenols of corn and low concentration of AFB1 was detected. Glucose supplement of CMA induced AFB1 production proving the need for free carbon source for the secondary metabolite pathway. The tolerance of the fungus against salt and cell membrane stress was lowered on CMA. At higher fatty acid concentration, the aflatoxin B1 production cannot be hindered by the natural antioxidants and that is important in selection of resistant corn hybrids.

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Hydrolytic enzyme production is typical of the autolysis in filamentous fungi; however, less attention has been given to the physiological role of the enzymes. Here, the aim was to investigate the possible relation of the chitinolytic enzymes to the changes in the biomass in some filamentous fungi of high importance for pharmaceutical or food industry. In Penicillium and Aspergillus filamentous fungi, which showed different characteristics in submerged cultures, the growth and biomass decline rates were calculated and correlated to the chitinase and N-acetyl-β-D-glucosaminidase enzyme productions. Correlation was found between the biomass decrease rate and the chitinase level at the stationary growth phase; while chitinase production covariates negatively with N-acetyl-β-D-glucosaminidase activities. The chitinase production and the intensive autolysis hindered the production of N-acetyl-β-D-glucosaminidase and, therefore, could hinder the cell death in the cultures.

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NADPH is involved in many basically important anabolic processes. For a long time, pentose phosphate pathway (PPS) was regarded as the most important source of NADPH in fungi. Here we present evidence of a metabolic switch to an alternative NADPH-producing pathway in ageing Penicillium chrysogenumcultures, which involves NADP+-specific isocitrate dehydrogenase (NADP+-ID) rather than PPS enzymes. Considering the main biochemical functions of NADPH, we propose that NADP+-ID could have deep impact on many physiological processes switched on glucose deprivation including proteinase production or penicillin biosynthesis. We also demonstrate that although the alternative pathway was inferior to PPS when the fungus was grown on well-utilisable carbon sources yet it could have an important role in fatty acid biosynthesis as well as in the maintenance of high intracellular NADPH/NADP+ratios.

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Acta Biologica Hungarica
Authors: A. Mádi, Tünde Pusztahelyi, Mária Punyiczki and L. Fésüs

The complete identification of coding sequences in a number of species has led to announce the beginning of the post-genomic era, new tools have become available to study complex phenomena in biological systems. Rapid advances in genomic sequencing and bioinformatics have established the field of genomics to investigate thousands of genes' activity through mRNA display. However, recent studies have demonstrated a lack of correlation between the transcriptional profiles and the actual protein levels in cells, so investigation of expressed part of the genome is also required to link genomic data to biological function. It is possible, that evolutional development occurred by increasing complexity of regulation processes at the level of RNA and protein molecules instead of simple increase in gene number, so investigation of proteins and protein complexes became a very important field of our post-genomic era. High-resolution two-dimensional gels combined with sensitive mass spectrometry can reveal virtually all proteins present in cells opening new insights into functions of cells, tissues and whole organisms.

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Under carbon starvation, Aspergillus nidulans produced a fungal/bacterial type chitinase, ChiB. The chiB gene was cloned and subcloned into pJC40 expression vector containing a 10XHis fusion tag, and the ChiB protein was expressed heterologously in Escherichia coli . Recombinant and native ChiB enzymes shared the same optimal pH ranges and showed similar substrate specificities with endo-acting cleavage patterns.

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There are extensive data on effects of antifungal agents on the plant pathogens, especially on Fusariums spp. species. However, investigations on the interaction of chemicals and the treated cultivars are rare. The aim of the study was to test two types of fungicide mixtures, azoxystrobin-propiconazole, and prothioconazole-tebuconazole, which are applied in wheat cultivars intensively, on six fodder maize hybrids that were infected with Fusarium proliferatum in the R1 growth stage in a field trial. The effect of the fungicide treatment was tested on the starch content and antifungal, antioxidant polyphenols of the kernels in the R3–R4 and R6 stage of the cultivars. The level of the fungal presence and the fumonisin concentration of the kernels were increased significantly under the artificial infection. The fumonisin concentration was variable at the R6 stage of the hybrid maize kernels. The treatment with prothioconazole and tebuconazole was found to be suitable when it was done before flowering, while the azoxystrobin-propiconazole treatments were equally successful before and after maize flowering considering the decreasing fumonisin concentration of the kernels. Both fungicide mixtures, when they were applied after maize flowering, affected the starch biosynthesis to the R3–R4 stage significantly. Meanwhile, azoxystrobin-propiconazole also significantly affected the antioxidant flavone/flavanol contents from the R3–R4 stage to the R6 stage.

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Acta Microbiologica et Immunologica Hungarica
Authors: T. Emri, Brigitta Oláh, L. Sámi, Zs. Molnár, Márta Nagy, Tünde Pusztahelyi and I. Pócsi
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