Constitutive expression of a novel isoamylase from Bacillus lentus in Pichia pastoris for starch processing

Isoamylase is essential to saccharifying starch by cleavage of 1,6-glucoside linkages in starch molecules. In this study, a novel isoamylase gene from Bacillus lentus JNU3 was cloned. The open reading frame of the gene was 2412 base pairs long and encoded a polypeptide of 804 amino acids with a calculated molecular mass of 90 kDa. The deduced amino acid sequence shared less than 40% homology with that of microbial isoamylase ever reported, which indicated it was a novel isoamylase. A constitutive GAP promoter was used to express the recombinant isoamylase in the yeast Pichia pastoris by continuous high cell-density fermentation to avoid the use of methanol, which resulted in 318 U/mL extracellular isoamylase activity after 72 h in a 10 L fermenter. The recombinant enzyme was purified and characterized. It had an estimated molecular mass of 90 kDa, with its optimal activity at 70 °C, pH 6.5 and was quite stable between 30 °C and 70 °C. The recombinant isoamylase proves to be superior to pullulanase as an auxiliary enzyme in maltose production from starch. Therefore it will contribute significantly to the starch debranching process.     

表面活性剂对D-阿拉伯糖醇发酵的影响

为提高D-阿拉伯糖醇的产量,研究不同类型表面活性剂对德巴利汉逊酵母(Debaryomyces hansenii)发酵生产D-阿拉伯糖醇的影响。结果表明:阳离子和阴离子表面活性剂对D-阿拉伯糖醇的生成几乎没有影响,部分非离子表面活性剂对D-阿拉伯糖醇的生产有促进作用,其中Trition X-100的影响最为显著。在不同发酵时间加入不同浓度的Trition X-100均对D-阿拉伯糖醇的生产有促进作用,当发酵24 h添加30 g/LTrition X-100时,D-阿拉伯糖醇的产量达到最高(92.9 g/L),相比于对照增加了27.2%。     

嗜热菌来源的生淀粉酶分离纯化及其酶学性质

从嗜热菌库中分离到两株能水解生淀粉的菌株173和174,通过扩增和测定两株菌的16S rDNA序列并进行比对结果表明,所分离两株菌属于Geobacillus属的细菌.液体摇瓶发酵菌株173、174,其产生的生淀粉酶(简称RSDE173、RSDE174)活力分别达14.5 U/mL和12.9 U/mL.通过生淀粉吸附-熟淀粉洗脱系统和TOYOPEARL HW-55F系统进行分离纯化,得到纯化的RSDE173和RSDE174,纯化倍数分别为50和29,活力回收率分别为34%和41%.有关RSDE173和RSDE174酶学性质研究显示.对熟淀粉水解的最适作用温度均为70℃,而对生淀粉水解则分别在50℃～60℃和40℃～60℃下表现出高水解活力;对不同底物的最适作用pH值均为5.0～5.5;它们对大多数试验离子的敏感性较低,但个别离子如Co2 、Cu'2 对RSDE173或u'2 对RSDE174的酶活力有一定的抑制作用.纯化的这两种生淀粉酶对不同来源生淀粉的底物专一性并不相同.RSDE173底物专一性顺序为红薯淀粉>小麦淀粉>玉米淀粉>木薯淀粉>糯米淀粉;而RSDE174的糯米淀粉>小麦淀粉>红薯淀粉>玉米淀粉>木薯淀粉.RSDE173对生红薯淀粉有很好的降解,其水解糊化淀粉与生红薯淀粉的比值为1.48;而RSDE174优先降解生糯米淀粉,其相应比值为1.69.     

贵州凯里生物群中软舌螺的初步研究

本文描述了采自贵州台江县革东镇八郎中寒武世凯里生物群中的软舌螺化石,计有1种,3相似种和1个未定种。即：Ambrolinevitus cf.ventricosus,Glossolites?sp..Haplophrentis?cf.carinatus,Linevitus opimus,Hyolithes?cf.cariniferus.凯里生物群中软舌螺特点是：1)壳体通常较大,呈宽锥形;2)背、腹壳区分明显,常具中槽或中脊;3)特别是以软舌螺目中的软舌螺科和线带螺科的软舌螺保存数量最多。完全与欧洲、北美相当层位中出现的软舌螺组合面貌相似;并与澄江动物群中的软舌螺在演化特征上是可衔接的。凯里生物群中的软舌螺除具有世界性属种外。还具地区特有的属种。这对研究软舌螺的地理分布、演化进程以及与凯里生物群组合关系有重要意义。     

窄头叶蝉属中国种类记要(同翅目,叶蝉科,叶蝉亚科)

共记述了中国窄头叶蝉属Batracomorphus Lewis20种。其中包括7新种：古丈窄斗叶蝉B.guzhangensis sp.nov．、齿突窄头叶蝉B.dentestyleus sp．nov.、叉突窄头叶蝉B.furcatus sp.nov.、细突窄头叶蝉B.gracilis sp.nov．、阔突窄头叶蝉B.lateprocessus sp．nov．、片马窄头叶蝉B.pianmaensis sp.nov．和斑翅窄头叶蝉B.puncta-tus sp．nov．;9个新组合。新种模式标本保存在贵州大学昆虫研究所。     

贵州沟螺属一新种记述(前鳃亚纲,中腹足目,环口螺科)

在整理贵州省荔波县茂兰喀斯特森林自然保护区陆生贝类标本时,经鉴定发现1新种,即茂兰沟螺Dioryx maolanensis sp.nov.,文中对新种形态特征、栖息环境进行了描述,并对其相似种进行了分析和讨论.     

High-efficient production of citric acid by Aspergillus niger from high concentration of substrate based on the staged-addition glucoamylase strategy

Bioprocess and Biosystems Engineering - Citric acid (CA), an important platform-compound, has attracted much attention because of its broad applications and huge market demand. To solve high...     

代谢工程改善野生酵母利用木糖产乙醇的性能

从256个自然样品中筛选得到1株可高效转化D-木糖的酵母。通过生理生化和分子生物学方法鉴定, 证实该菌株是属于Candida tropicalis。以该酵母为研究对象, 增加木糖醇脱氢酶表达量, 通过改变代谢流以达到提高酒精产率的目的。以pXY212-XYL2质粒为基础载体, 构建了含有潮霉素抗性的pYX212-XYL2-Hygro, 电击转化进入野生型C. tropicalis, 潮霉素抗性筛选, 得到含高拷贝木糖醇脱氢酶基因的重组菌株C. tropicalis XYL2-7。重组菌的比酶活达到0.5 u/mg protein, 比原始菌株提高了3倍。实验表明, 重组菌木糖醇得率比原始菌株降低了3倍, 酒精得率提高了5倍。首次通过实验验证了热带假丝酵母利用木糖产乙醇的可行性, 这对研究酵母利用秸秆、麦糠、谷壳等纤维质农业废弃物生产燃料乙醇具有重要启示。     

Unraveling the specific regulation of the shikimate pathway for tyrosine accumulation in Bacillus licheniformis

Journal of Industrial Microbiology & Biotechnology - l-Tyrosine serves as a common precursor for multiple valuable secondary metabolites. Synthesis of this aromatic amino acid in Bacillus...     

灭蚊真菌——大链壶菌原生质体形成和再生的研究

采用1％纤维素酶与1％真菌脱壁酶混合液作脱壁酶,0.6mol/L山梨醇为渗透压稳定剂,从摇床培养的12—14小时菌龄的大链壶菌(Lagenidium giganteum)菌丝体获得原生质体。酶解3—5小时后,产量可达1.4—2.0×10~6/mL。并在双层培养基上初步实现了原生质体再生。