Homologous Expression And Characterization Of The Xylanase From Aspergillus Niger

Xylan, composed of polysaccharide containingβ-1, 4-linked D-xylopyranosideresidues, is one of the major components of plant cell walls. Endo-β-1,4-xylanase(EC3.2.1.8) degrades the backbone ofβ-1, 4-linkages of xylose.Xylanase is widely applied in animal feed, medicine, food processing and papermanufacturing. However, the low yield of xylanase becomes a limiting factor to theuse of xylanase in various industries. The aim of my study is to construct a high levelxylanase recombinant in filamentous fungal expression system.The cDNA encoding the acidic xylanase from original A. niger TS1 wasamplified by RT-PCR and cloned into the eukaryotic expression vector pYG1.2 underthe control of the glaA promoter. The recombinant plasmids were transformed intopyrG deficient A. niger M54 host strain by protoplast transformation technology. Thishomologous expression system expressed xylanase activity of 507 IU/ml which wasmeasured in shake-flask cultures containing 1％xylan. This activity was 6.7-fold and3.89-fold higher than the activity for the original strain and host strain respectively.The maximum xylanase activity was obtained after culturing for 72 hours and thexylan induced enzymatic activity was 3.94-fold higher compared to non-inducedcondition. The optimum pH of recombinant xylanase was at 5.2,whereas the optimumtemperature was at 50℃and remained more than 63.95％activity even afterincubation at 60℃for 30min.It's the first time that high secreting expression system was constructed using ahomologous expression process in filamentous fungus. The promising resultsachieved in this study may have a good industrial perspective especially in the animalfeed.