Published in AgroLife Scientific Journal, Volume 6, Number 1
Written by Aglaia BURLACU, Florentina ISRAEL-ROMING, Călina Petruța CORNEA
Xylanases have numerous applications in various fields, thus presenting an immense interest in studying. The sources for these enzymes include bacteria, fungi, yeast and others, the most important producers being fungi. The focus of this study was on enhancing the fungal strain ability to produce xylanase using random mutagenesis. Several mutants from Aspergillus brasiliensis and Penicillium digitatum were obtained through physical and chemical mutagenesis from strains previously selected as xylanase producers. The Petri plates with the fungal spores were exposed to UV light for physical mutagenesis at the distance of 10 cm and for 5-50 minutes. The chemical mutagenesis involved the use of Nmethyl-N′-nitro-N-nitrosoguanidine and ethyl methane sulfonate, by adding in the Petri plates with the fungal spores 150 μg/ml mutagen (N-methyl-N′-nitro-N-nitrosoguanidine or ethyl methane sulfonate). After both physical and chemical mutagenesis, several mutant strains were randomly selected and subjected to a qualitative and quantitative screening for their ability to produce xylanase. For the qualitative screening, the selected strains were cultivated on selective xylan agar medium with 0.8% oat spelt xylan as the only carbon source. The plates were analysed at every 24 h for the occurrence and evaluation of the hydrolysis area, using Congo red staining. Based on the measurements of the halo diameter, several strains were selected for a quantitative screening, using the DNS assay for reducing sugars to determine the xylanase activity. In order to determine the specific enzymatic activity, the protein assay was carried out. The comparison of the studied strains showed that there are differences concerning the production of xylanase between the mutant strains and the original ones.
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