L-异亮氨酸分批发酵动力学模型的研究

对黄色短杆菌L－异亮氨酸高产菌XQ－4（AHV^rAEC^rSuc^gSG^rEth^rα－AB^rIleHx^r）分批发酵动力学模型进行了研究。建立了比较合理的L－异亮氨酸分批发酵动力学模型,为L－异亮氨酸补料分批发酵最优化的研究奠定基础。     

生产L——异亮氨酸的新方法

<正> 前言现在,已有许多生产L-异亮氨酸的报导,但是,由于菌株生长过程中需要大量消耗碳源,而且转化率很低,所以,这些方法的效果很差。本文描述了一种具有高产潜力的L-异亮氨酸的新生产方法。     

1株能利用高粱汁产L-乳酸的菌株鉴定及培养基优化

以产L-乳酸的菌株A2为对象,采用16S rRNA基因测序法结合菌株的表型特征进行鉴定,以甜高粱汁为主要培养基质,采用响应面设计软件对该菌种的发酵培养基进行优化。结果表明,A2菌株为Lactobacillus plantarum S4,优化得到的甜高粱汁培养基配比为甜高粱汁327. 83 g/L,蛋白胨1. 67 g/L,磷酸氢二钾4. 7 g/L,硫酸锰0. 17 g/L,在此培养基配比下,Lactobacillus plantarum S4厌氧发酵68 h后,L-乳酸产量达(61. 20±1. 36) g/L,L-乳酸/葡萄糖转化率(90. 74±2. 28)%,L-乳酸/蔗糖转化率(47. 20±1. 81)%。     

L-异亮氨酸高产菌选育及其培养基优化

旨在诱变选育L-异亮氨酸高产菌,并探索突变株最佳发酵条件。利用传统化学诱变结合常压室温等离子体生物诱变体系对实验室保藏的Brevibacterium flavum I-12进行逐级诱变,选育2-噻唑丙氨酸(2-TA)和磺胺胍(SG)高抗性和在琥珀酸平板上能快速生长的突变菌株。随后,在单因素实验的基础上,利用响应面设计优化出目的突变株摇瓶发酵培养基组分的最佳参数水平。结果显示,经过一系列诱变和筛选,成功选育出一株在40 g/L的2-TA和5 g/L的SG,且以琥珀酸为唯一碳源的培养基上快速生长突变株,命名为B. flavum TA-6,该菌株产酸达26.2±0.5 g/L,比出发菌株提高了44.75%,而副产物L-缬氨酸和L-亮氨酸积累量明显降低。经响应面法优化发酵条件后,突变株产酸可达27.8±0.5 g/L,比优化前提高了6.1%。通过传统化学诱变结合ARTP生物诱变体系,成功选育出一株杂酸降低的L-异亮氨酸高产菌TA-6,该菌株具有潜在生产应用价值。     

阿维菌素高产菌株的选育Ⅰ

目的：全面了解阿维菌产生菌S.avermitilis的生长特性并获得阿维菌素的高产菌株。方法：以S.avermitilis Y20为出发菌株,考察该菌株的菌落特征和发酵特性,分别利用紫外线（UV）、亚硝酸（HNO3）及亚硝基胍（NTG）并结合L－异亮氨酸（L－Ⅱe）诱导等手段对出发菌株Y20进行诱变处理。结果：获得高产阿维菌素变异株H336,发酵单位达到852μg/ml。结论：与出发菌株相比,突变株阿维菌素的产量稳定,发酵单位提高了10倍以上。     

L-异亮氨酸产生菌黄色短杆菌的选育

以黄色短杆菌BF420为出发菌株,经过紫外线和亚硝基胍(NTG)复合诱变处理后,获得一株甲硫氨酸缺陷(Met-)及抗α-氨基丁酸(α-AB)的L-异亮氨酸产生菌BM2610,该菌株在未进行优化的发酵条件下能够积累L-异亮氨酸的量为7.12g.L-1,比出发菌株BF420提高了122.5%。     

双组份转运系统BrnFE的过表达和表面活性剂的添加对谷氨酸棒杆菌发酵生产L-异亮氨酸的影响

为了提高L-异亮氨酸生产菌株Corynebacterium glutamicum LD320的产酸水平,通过改善其分泌系统,在C. glutamicum LD320中分别过表达突变型和野生型的双组份转运系统BrnFE操纵子,构建了重组菌LD320/pXMJ19-brnFE和LD320/pXMJ19-brnFE1。通过对两株重组菌的L-异亮氨酸生产分析比较,发现突变型比野生型能更有效地提高 L-异亮氨酸产量。同时对 LD320/pXMJ19-brnFE1进行表面活性剂添加实验,发现Tween-80为最佳选择,其最佳添加量为0.5 g/L,最佳添加时间为对数期的16 h。最后通过7 L发酵罐放大实验,LD320/pXMJ19-brnFE1的L-异亮氨酸产量由18.53 g/L提高到25.45 g/L,比对照组提高了37%。     

丙氨酸转氨酶修饰对大肠杆菌L-色氨酸合成的影响

探究大肠杆菌细胞内负责L-丙氨酸合成的转氨酶对菌株代谢及L-色氨酸合成的影响。运用Red重组技术分别对编码L-丙氨酸转氨酶的基因alaA、alaC和avtA进行敲除。通过摇瓶和50 L罐中探究其对L-色氨酸积累、L-丙氨酸代谢及菌体生长变化情况。结果显示,除3种L-丙氨酸转氨酶全部缺失的工程菌L-丙氨酸合成受阻、菌体生长受到较强抑制外,其它各任意一种或两种丙氨酸转氨酶缺失菌株的生长并未有较大差异,但色氨酸的合成变化显著。其中alaA和alaC双基因缺失的E.coli FS-T4工程菌,摇瓶发酵L-色氨酸产量达6.08 g/L,L-丙氨酸含量仅0.16 g/L,较出发菌株分别提高了26.7%和降低了91.0%。在50 L罐中E.coli FS-T4工程菌L-色氨酸产量最高可达41.9 g/L,糖酸转化率达20.5%,分别较出发菌株提高了13.8%和5.1%。转氨酶AlaA和AlaC的同时缺失,既可以满足细胞整体氨基酸池的需要,而且有利于减少杂酸的积累,使得更多的碳源流向L-色氨酸的合成。     

酿酒酵母POS5基因过表达对L-异亮氨酸合成的促进作用

L-异亮氨酸是人体必需氨基酸之一,具有很大的商业价值。在谷氨酸棒杆菌中,合成一分子L-异亮氨酸需要消耗四分子NADPH。因此,提高胞内NADPH浓度是提高L-异亮氨酸产量的重要手段之一。在乳糖发酵短杆菌JHI3-156中过量表达酿酒酵母的NADH激酶编码基因POS5△MTS,发酵48 h表达菌株JHI3-156/pDXW-10-POS5△MTS的胞内NADP~+浓度增加了27μmol/L(17%),NADPH浓度增加了36μmol/L(96%);发酵72 h后L-异亮氨酸产量是(3.02±0.52)g/L,比对照菌(1.96±0.04)g/L提高了54%。本研究表明,过表达POS5△MTS基因能提高NADPH的供应,促进了L-异亮氨酸的生物合成。     

L-苏氨酸工业生产发酵条件优化研究

发酵法生产L-苏氨酸是目前广泛采用的方法,因此研究工业生产发酵条件优化具有重要意义。试验以高产L-苏氨酸菌作为出发菌株,结合本公司的实际工业生产条件对发酵各条件进行了一系列优化研究,结果表明：添加0.2%的工业级生长促进剂,以复合糖代替葡萄糖为初糖,并控制初糖浓度在60g/L,除生长高峰期外,发酵过程中溶解氧（DO）控制在10%~20%之间;最终发酵放罐湿菌体在45g/L左右,L-苏氨酸含量可达110g/L左右。     

Recent advances in the study of Kaposi's sarcoma-associated herpesvirus replication and pathogenesis

It has now been over twenty years since a novel herpesviral genome was identified in Kaposi's sarcoma biopsies. Since then, the cumulative research effort by molecular biologists, virologists, clinicians, and epidemiologists alike has led to the extensive characterization of this tumor virus, Kaposi's sarcoma-associated herpesvirus(KSHV; also known as human herpesvirus 8(HHV-8)), and its associated diseases. Here we review the current knowledge of KSHV biology and pathogenesis, with a particular emphasis on new and exciting advances in the field of epigenetics. We also discuss the development and practicality of various cell culture and animal model systems to study KSHV replication and pathogenesis.     

The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae)

Comprises species occurring mostly in subtidal habitats in tropical, subtropical and warm-temperate areas of the world. An analysis of the type species, V. spiralis (Sonder) Lamouroux ex J. Agardh, a species from Australia, establishes basic characters for distinguishing species in the genus. These characters are (1) branching patterns of thalli, (2) flat blades that may be spiralled on their axis, (3) width of the blade, (4) primary or secondary derivation of sterile and fertile branchlets and (5) position of sterile and fertile branchlets on the thalli. Application of the latter two characters provides an important basic method for separation of species into three major groups. Osmundaria , a genus known only in southern Australia, was studied in relation to Vidalia , and its separation from the Vidalia assemblage is not accepted. Species of Vidalia therefore are transferred to the older genus name, Osmundaria. Two new species, Osmundaria papenfussii and Osmundaria oliveae are described from Natal. Confusion in the usage of the epithet, Vidalia fimbriala Brown ex Turner has been clarified, and Vidalia gregaria Falkenberg, described as an epiphyte on Osmundaria pro/ifera Lamouroux, is revealed to be young branches of the host, Osmundaria prolifera.     

New or rare chromosome counts in Artemisia L. (Asteraceae, Anthemideae) and related genera from Kazakhstan

Fifteen chromosome counts of six Artemisia taxa and one species of each of the genera Brachanthemum, Hippolytia, Kaschgaria, Lepidolopsis and Turaniphytum are reported from Kazakhstan. Three of them are new reports, two are not consistent with previous counts and the remainder are confirmations of very scarce (one to four) earlier records. All the populations studied have the same basic chromosome number, x = 9, with ploidy levels ranging from 2x to 6x. Some correlations between ploidy level, morphological characters and distribution are noted.     

肝癌中HBV和HCV基因和抗原的分布及意义

采用原位分子杂交方法检测HCV RNA及HBV X基因;采用免疫组织化学方法研究HCV核心抗原,非结构区C33c抗原及HBxAg在肝细胞肝癌中的定位及分布.结果表明(1)HCV RNA、HBV X基因在肝细胞肝癌组织检出率分别为40%(55/136)和82%(112/136).HCV RNA定位于癌细胞的胞浆内,阳性细胞呈散在、灶状及弥漫分布三种形式;HBV X基因在肝癌细胞中的分布呈胞浆型、核型及核浆型,阳性细胞也呈上述三种分布形式;(2)HCV C33c抗原、核心抗原在肝细胞肝癌中的阳性率为81%(133/164)及86%(141/164).C33c抗原定位于癌细胞及肝细胞的胞浆内;核心抗原既定位于癌细胞核中,又可定位于胞浆中.C33c抗原阳性细胞以灶状分布为主;而核心抗原阳性细     

Selection with two alleles and complete dominance

For a plant selection model with frequency-independent viabilities, fertilities and selfing rates, it is shown that apart from global fixation, for certain parameter combinations a protected polymorphism and facultative fixation (either allele may become fixed according to initial frequencies) may both occur. Facultative fixation requires different selling rates for the dominant and recessive type. Protection of the polymorphism requires resource allocation for male and female function. In this connection the problem of purely genetically caused population extinction is discussed.
For general frequency dependence and regular segregation, the chances for establishment of a completely recessive gene are compared to those of a completely dominant gene. It is proven that the process of establishment of the recessive gene, despite a fitness advantage, may be considerably endangered by drift effects if random mating prevails. The recessive gene may reach the same effectivity in establishment as a dominant gene, only if the recessive homozygote mates exclusively with its own type during the period of establishment.