一株降解生木薯淀粉的曲霉菌株的筛选、鉴定及其淀粉降解特性

Screening and Identification of a Raw Cassava Starch-hydrolyzing Aspergillus Strain and Its Characteristics of Starch Degradation

本研究利用以生木薯淀粉为唯一碳源的筛选培养基,从腐烂木薯渣中分离筛选出一株可以降解生木薯淀粉的真菌菌株RSDF-7。根据RSDF-7形态和18SrDNA与28SrDNA之间的内转录间隔区(internal transcribed spacer,ITS)序列分析的结果,初步认定该菌株为曲霉属。菌株RSDF-7的粗酶液对多种不同的生淀粉底物均有水解效果;在以大米和玉米淀粉为底物时,其生淀粉分解活力比较高,分别为42%和40%。菌株RSDF-7的粗酶液具有良好的低pH稳定性,对生木薯淀粉的最适作用温度为50℃,最适作用pH为4.5。在30min的吸附后,RSDF-7的粗酶液对生木薯淀粉的吸附力高达60%。使用HPLC对粗酶液的酶解产物进行检测,结果发现酶解产物中仅存在葡萄糖,表明菌株RSDF-7所产的生淀粉降解酶主要为糖化酶。扫描电镜观察结果发现,经RSDF-7粗酶液酶解后的生木薯粉颗粒破裂,形成空洞,说明RSDF-7粗酶液对生淀粉有较强的水解作用。可以预见,经纯化后的曲霉菌株RSDF-7生淀粉酶将来可以用于基于酶解的木薯淀粉转化。

A raw cassava starch-hydrolyzing fungal,numbered as RSDF-7,was isolated and screened from the decayed cassava dreg using the screening medium with raw cassava starch as the sole carbon resource.The crude enzyme of strain RSDF-7 showed the better stability within a lower range of pHs.The optimum temperature for digestion of raw starch was 50℃,and the optimum pH was at 4.5.The crude enzyme from the culture of RSDF-7 could hydrolyze several different raw starch substrate,the values of raw starch-degrading ability were higher,with about 42% and 40% using corn and rice starch as the substrate,respectively.Analysis of the morphology and internal transcribed spacer region sequence between 18S rDNA and 28S rDNA indicated that the RSDF-7 belongs to Aspergillus sp..The absorption rate of raw cassava starch by RSDF-7 was about 60% after 30 min adsorption.Assay of high performance liquid chromatography indicated that the enzymatic product of raw cassava starch by the crude enzyme from RSDF-7 was only glucose,suggesting that the crude enzyme produced by RSDF-7 is starch-digesting glucoamylase.The scanning electron microscope revealed that the raw cassava starch granules ruptured and presented larger cavities after digestion treatment with the crude enzyme,indicating that the enzyme has a stronger ability to digest the raw starch.It was expected that enzyme from Aspergillus strain RSDF-7 after purification can be used in enzymatic-based digestion conversation of cassava starch in future.