重组肺炎克雷伯氏菌转化甘油为聚3-羟基丙酸

聚3-羟基丙酸[Poly(3-hydroxypropionate),P3HP]是一种生物可降解及生物相容的新型聚羟基脂肪酸酯。目前已鉴定的生物均不能天然合成P3HP。采用PCR克隆鼠伤寒沙门氏菌的丙醛脱氢酶(Pdu P)基因及罗尔斯通氏菌的聚羟基脂肪酸酯合成酶(Pha C)基因,构建共表达载体,转化肺炎克雷伯氏菌后获得两株重组菌。以甘油为唯一碳源进行摇瓶发酵,pdu P和pha C共用tac启动子的工程菌K.p(p ET-tac-pdu P-pha C)产生0.054 g/L的P3HP,而pdu P和pha C各自独用tac启动子的工程菌K.p(p ET-tac-pdu P-tac-pha C)产生0.091 g/L的P3HP。     

重组大肠杆菌转化甘油合成聚3-羟基丙酸-co-乳酸

聚羟基脂肪酸酯作为性质优良的生物塑料,引起了广泛的关注。由于聚羟基脂肪酸合成酶PhaC特异性较强,难以通过生物合成方法获得含乳酸单体聚合物。为了实现乳酸的聚合,PhaC的筛选至关重要。以甘油为底物,通过引入Klebsiella pneumoniae的甘油脱水酶DhaB123及其激活因子GdrAB以及Salmonella typhimurium LT2的丙醛脱氢酶基因PduP,获得3-羟基丙酰辅酶A;通过引入Megasphaera elsdenii DSM 20460的丙酰辅酶A转移酶PCT,获得乳酰辅酶A;并对3种不同聚羟基脂肪酸合成酶的作用进行考察。在Pseudomonas putida的原始酶PhaC1或者PhaC2的作用下,不能实现乳酸的聚合;而在双位点突变(Ser325Thr和Gln481Lys)的PhaC1(STQK)存在条件下,重组菌可以利用甘油合成聚3-羟基丙酸-co-乳酸。经过对溶氧、有机氮源等发酵条件的优化,聚3-羟基丙酸-co-乳酸的产量可以达到0.22g/L,占细胞干重的3.2%,是含乳酸单体聚合物生物合成研究的一次有益尝试。     

聚羟基烷酸酯 (PHA) 改性研究进展

本文简述了生物制造聚羟基烷酸酯(PHA),包括聚3-羟基丁酸酯(PHB)、聚(3-羟基丁酸酯-3-羟基戊酸酯)(PHBV)、聚(3-羟基丁酸酯-4-羟基丁酸酯)(P3/4HB)、聚(3-羟基丁酸酯-3-羟基己酸酯)(PHBH)的产业化现状,综述了针对PHA材料热稳定性差、加工窗口较窄等缺点而进行的一些改性研究。选用适当方法对PHA进行改性,可使其性能得到优化,应用领域得到拓展。     

生物合成3-羟基丙酸的代谢工程研究进展

3-羟基丙酸(3-HP)作为一种重要的平台化合物,以此为底物能够合成多种具有商业潜质的生物制品。野生菌合成3-HP产量较低,严重限制3-HP的大规模应用与生产,通过改造合成代谢通路的相关基因,构建以廉价底物为碳源的工程菌株,实现降低生产成本提高产量的目的。文中将对近年来国内外通过代谢工程合成3-羟基丙酸的研究进展进行概述,并对甘油途径、丙二酸单酰辅酶A途径、β-丙氨酸等途径合成3-HP的优缺点进行总结分析,对3-HP未来发展前景进行展望。     

前体代谢工程提高红霉素产量的研究进展

红霉素是十四元大环内酯类抗生素,具有广泛的医药价值和巨大的新药开发潜力。红霉素的主要成分红霉素A由丙酰辅酶A和甲基丙二酰辅酶A作为前体通过聚酮合酶合成大环内酯骨架,再经羟基化、糖基化、甲基化等一系列修饰合成。根据红霉素A的生物合成路线,我们从前体喂养途径、糖基化和甲基化优化等方面,简要综述近年来利用前体代谢工程手段提高红霉素产量的研究进展。     

弱化呼吸链水平对代谢工程大肠杆菌聚羟基丁酸乳酸酯合成的影响

聚3-羟基丁酸乳酸酯[Poly(3-hydroxybutyrate-co-lactate), P(3HB-co-LA)],属于聚羟基脂肪酸酯(Polyhydroxyalkanoates,PHA)家族的一员,是一种具有良好生物相容性和可降解性的天然高分子生物材料。文中通过在大肠杆菌中引入来源于富养罗尔斯通氏菌Ralstonia eutropha的β-酮硫解酶、乙酰乙酰Co A还原酶、来源于丙酸梭菌Clostridium propionicum的丙酰Co A转移酶突变体以及荧光假单胞菌Pseudomonas fluorescens strain 2P24来源的PHA合成酶突变体等异源酶,成功实现了一步法利用葡萄糖合成P(3HB-co-LA),其中乳酸组分的摩尔百分比达到1.6%,聚合物含量为83.9wt%。在此基础上,通过敲除辅酶Q8合成所需的黄素异戊烯基转移酶基因(ubi X)来弱化呼吸链水平,从而增强乳酸积累,并进一步缺失乳酸脱氢酶基因(dld)以减少乳酸在发酵后期转化成丙酮酸,最终将P(3HB-co-LA)中乳酸组分的摩尔百分比提高至14.1%,而聚合物含量为81.7wt%。上述实验结果表明,采用弱化呼吸链水平策略可有效提高聚合物中乳酸组分的摩尔百分比,从而提供了一种改变生物合成聚合物中单体组分含量的新思路。     

重组大肠杆菌合成聚(3-巯基丙酸)和聚(3-羟基丁酸-3-巯基丙酸)的研究

利用Clostridium acetobutylicum的丁酸激酶基因 (buk) 和磷酸转丁酰基酶基因(ptb),以及Thiocapsa pfennigii的PHA合成酶基因,设计了一条能够合成多种聚羟基烷酸的代谢途径,用构建的质粒转化大肠杆菌,获得了重组大肠杆菌菌株.前期的研究表明,在合适的前体物条件下,该重组大肠杆菌能够合成包括聚羟基丁酸、聚(羟基丁酸-戊酸)等多种生物聚酯[Liu and Steinbüchel, Appl. Environ. Microbiol. 66739-743].利用该重组大肠杆菌,通过生物催化作用合成了3-巯基丙酸的同型共聚酯,同时利用该重组大肠杆菌还获得了含3-巯基丙酸单体的多种异型共聚物.实验首先研究了3-巯基丙酸对大肠杆菌生长的影响,在此基础上优化了培养过程中添加3-巯基丙酸的时机和浓度,结果表明,在实验的条件下,细胞合成聚(3-巯基丙酸)可达6.7%(占细胞干重),合成聚(3-羟基丁酸-3-巯基丙酸)(分子中3-巯基丙酸3-羟基丁酸=31)可达24.3%.实验进一步研究了同时或分别表达以上3个基因的重组大肠杆菌合成聚合物的能力,结果表明只有当3个基因同时表达时才能合成聚合物,说明3个基因对合成过程是必须的,从而表明了合成途径是按照设计的路线进行的.还通过GC/MS、GPC、IR等手段对合成的化合物进行了定性的研究.聚(3-巯基丙酸)或聚(3-羟基丁酸-3-巯基丙酸)等聚酯属于一类新型生物聚合物,它在分子骨架中含有硫酯键,不同于聚羟基烷酸酯的氧酯键,从而具有显著不同的物理、化学、光学等性质和具有重要的潜在应用价值.     

ε-聚赖氨酸的微生物合成与降解

ε-聚赖氨酸为一种均聚氨基酸,由单个赖氨酸分子在α-羟基和-ε氨基形成酰胺键而连接成的多聚体,目前主要通过白色链霉菌(Streptomyces albulus)的微生物合成进行生产,具有抑菌谱广、热稳定性好、在酸碱条件下稳定等特点,作者综述了ε-聚赖氨酸微生物合成的方法、可能的生物合成和降解机制等,并简要介绍ε-聚赖氨酸作为食品保鲜剂在食品和生物高分子材料在基因治疗、药物载体、基因芯片、高吸水性材料等方面的应用前景。     

高分子聚合物的微生物合成与废弃物资源化

γ- 聚谷氨酸(γ-PGA)、γ- 聚苹果酸(γ-PMA)、细菌纤维素(BC)和聚羟基脂肪酸酯(PHA)等都是微生物合成的重要生物高分子聚合物.     

热稳定酯酰辅酶A合成酶的异源表达及酶学特性

【目的】为寻找能合成丙酰辅酶A和丁酰辅酶A等聚酮合成前体的生物催化剂,用体外酶学实验对一个酯酰辅酶A合成酶进行了表征。【方法】利用丙二酰辅酶A合成酶作为输入序列,通过BLAST程序在Caldicellulosiruptor owensensis OL的基因组中找到1个酯酰辅酶A合成酶基因。在大肠杆菌中进行了异源表达,并通过亲和层析进行纯化。底物谱、最适反应条件、稳定性和动力学参数通过体外酶学实验进行表征,而定点突变则用于活性中心的氨基酸残基的分析。【结果】该酶具有较好的底物宽泛性,可识别丙酸、丁酸、2-甲基丙酸、戊酸、3-甲基丁酸、2-甲基丁酸以及环己甲酸等一系列单酸。反应最适温度为30°C,最适p H为7.0。70°C保温8 h后仍有45%的活性残留,表明该酶相对比较稳定。通过活性中心3个位点的定点突变可以改变酶的底物特异性。【结论】C.owensensis OL来源的酯酰辅酶A合成酶是潜在的生物催化剂,可以用于聚酮前体的合成。     

六种藓类植物茎的比较解剖学研究

通过对6种藓类植物,即褶叶青藓(Brachythecium salebrosum(Web.et Mohr.)B.S.G.)、湿地匐灯藓(Plagiomnium acutum(Lindb.)Kop.)、侧枝匐灯藓(Plagiomnium maximoviczii(Lindb.)Kop.)、大凤尾藓(Fissidensnobilis Griff.)、大羽藓(Thuidium cymbifolium(Doz.et Molk.)B.S.G.)和大灰藓(Hypnum plumaeforme Wils.)嫩茎和老茎的石蜡切片和显微观察发现,同一藓类植株的嫩茎和老茎,茎结构稳定,不同种藓类植物茎横切面具有不同特征.植物体茎横切面形状、表层细胞的层数、细胞大小和细胞壁厚薄、皮层细胞大小和形状、中轴的有无以及比例等特征可以作为藓类植物的分科分类依据之一.     

真菌类遗传学分析的知识结构教学

本文以认知结构理论为指导,讨论了真菌类遗传分析与高等动植物遗传分析的内在联系,认为利用这种内在联系进行教学可收到好的效果并说明了作者的具体教学过程。 Abstract:In the paper, the relationship between genetic analysis of Fungi and genetic analysis of high animal and plant was discussed.A good results were obtained when we adopted this method in the teaching.     

Cause of Senescence of Nine Sorts of Flowers

The levels of endogenous phytohormones and respiratory rate in nine sorts of flowers such as Cymbidium faberi Rolfe, Nopalxochia ackermannii Kunth and others were investigated both at full bloom and senescence and meanwhile the effect of exogenous phytohormones on prolonging the blossoms and promoting ethylene production were tested. There is a high content of endogenous ethylene in all the long-lived flowere, about 3–16 folds higer than the short-lived ones. There is a high level of ABA at full blooming flowers of short-lived flowers, in which there is no or only some cytokinins in it, but the ratio of CTK (6BA+zeatin)/ABA is smaller(l.7). The endogenous ABA reached a much higher level at senescence in all nine sorts of flowers, so it is reasonable to consider that it is ABA which plays an important role of regulation in controlling flower's senescence. There is a much higher level of GA3 and zeatin in the long-lived flowers which is not demonstrated in the shortlived ones. The respiratory rate is one of the factors controtling the longevity of flowers, but it does not play a decided role. Application of 6BA and zeatin prolongs distinctly orchid’s longevity, however exogenous IAA through the promotive action on ethylene production, evidently extends the longevity of the flowers of the Nopalxochia ackermannii Kunth.     

Time of detection of recessive genes: effects of system of mating and number of examined individuals

Summary Anthers were cultured from two sets of seven lines of hexaploid wheat (Triticum aestivum L.) with different cytoplasms, the euplasmic nucleus donors, Siete Cerros 66 and Penjamo 62, as well as their six alloplasmic lines derived from wild relative species of the genera Triticum and Aegilops. Significant cytoplasmic and nuclear effects but no cytoplasmic-nuclear interaction were found for embryogenic anther response, with the best performance of Penjamo 62 in Ae. kotschyi cytoplasm. Plant regeneration was not affected significantly by the cytoplasmic background of the lines cultured. The possible genetic implications of the observed cytoplasmic and nuclear influences on the in vitro haploid induction of wheat are discussed.     

龙胆科药用植物化学成分的研究现状

龙胆科植物在我国的分布范围很广,且多数为药用植物,其多数种属的药用植物,至今其化学成分尚未被系统研究。综述了目前龙胆科药用植物的化学成分的研究现状及一般提取方法,对近年来发现的环烯醚萜及裂环烯醚萜类化合物进行了总结,为本科药用植物的更深入研究提供了参考。     

Photoregulation of seed germination of wild-type and of an aurea-mutant of tomato

Seed germination of an aurea mutant of tomato ( Lycopersicon esculentum Mill.) is promoted by continuous irradiation with red, far-red or long-wavelength far-red (758 nm) light as well as by cyclic irradiations (5 min red or 5 min far-red/25 min darkness). Far-red light applied immediately after each red does not change the germination behaviour. Seed germination of the isogenic wild-type, cv. UC-105, is promoted by continuous and cyclic red light while it is inhibited by continuous and cyclic far-red light and by continious 758 nm irradiation. Far-red irradiation reverses almost completely the promoting effect of red light. The promoting effect (in the aurea mutant) and the inhibitory effect (in the wild-type) of continuous far-red light do not show photon fluence rate dependency above 20 nmol m⁻² s⁻¹. It is concluded that phytochrome controls tomato seed germination throgh low energy responses in both the wild type and the au mutant. The promoting effect of continuous and cyclic far-red light in the au mutant can be attributed to a greater sensitivity to P_fr.     

Scales of spatial patterns of distribution of intertidal invertebrates

Few comparative studies of spatial patterns at different scales have examined several species in the same habitat or the same species over a range of habitats. Therefore, variability in patterns among species or among habitats has seldom been documented. This study quantifies spatial patterns of a suite of intertidal snails and a species of barnacle using a range of statistical techniques. Variability in densities was quantified from the scale of adjacent quadrats (over a distance of centimeters) to tens of kilometers. Significant differences in abundances occurred primarily at two spatial scales. Small-scale differences were found at the scales of centimeters or 1–2 m and, for many species on many shores, these accounted for most of the variability in abundances from place to place. These are likely to be determined by behavioural responses to small-scale patches of microhabitat. Large-scale differences in abundance were also found in most species at the scale of hundreds of meters alongshore. These are likely to be due to variation in recruitment (and/or mortality) because of limited dispersal by adults of these species. There was little or no additional variation among shores, separated by tens of kilometers, than was shown among patches of shore separated by hundreds of meters. Identification of the scale(s) at which significant differences in abundance are found focus attention on the processes (and the scales at which these processes operate) that influence patterns of distribution and abundance. Some of the advantages and disadvantages of various procedures are discussed.