2,4-二氨基喹唑啉衍生物的抑菌活性研究

喹唑啉衍生物具有广泛的生物活性,包括抗菌活性。为发现此类化合物中具有潜在抑菌活性的化合物,本研究考察了15种带有哌嗪二硫代甲酸酯侧链的2,4-二氨基喹唑啉衍生物7a~7o的抑菌活性。首先采用分子对接方法对底物与酶的结合能进行预测,并用标准2倍稀释法测定这15种化合物对多重耐药大肠埃希菌的最小抑菌浓度(minimum inhibitory concentration,MIC)。结果表明,15种化合物与阳性对照相比均具有较好的抑菌活性。化合物7a、7g和7k具有明显的抑菌活性,其MIC均≤1mg/mL。进一步采用高效毛细管电泳筛选模型对7a、7g和7k进行分子水平抑菌实验,分别测定其抑制率与半数抑制浓度(half inhibitory concentration,IC50),发现化合物7k具有最佳抑制活性(IC_(50)为4.97×10~(-2) mg/mL)。此外,对15种化合物抑菌活性构效关系的研究表明,苯环上连有吸电子基团的哌嗪二硫代甲酸酯侧链对抑菌活性有贡献。这一研究有望为抑菌药物的研发提供有效的先导化合物。     

拟南芥2-甲基-6-叶绿基-1,4-苯醌甲基转移酶启动子的分离及表达特性分析

维生素E是一类人体必需的脂溶性抗氧化剂, 具有重要的生理功能。2-甲基-6-叶绿基-1,4-苯醌甲基转移酶(MPBQ MT)是天然维生素E合成途径中的关键酶之一, 催化MPBQ甲基化, 生成DMPBQ。从拟南芥分离了MPBQ MT基因1018bp的启动子序列, 构建了含该启动子和GUS报告基因的植物表达载体, 通过农杆菌介导转化拟南芥, 获得了转基因植株。GUS组织化学染色结果表明, 在MPBQ MT启动子驱动下, 报告基因GUS在拟南芥的茎、叶、花萼、雄蕊、种荚均有表达, 且在茎、叶、种荚中表达量较高, 而在根、花瓣和种子中则没有观察到GUS基因的表达, 表明MPBQ MT基因可能仅在拟南芥幼嫩茎、叶、种荚等绿色组织中特异性高表达。     

s-三唑[3,4-b]-1,3,4-噻二嗪衍生物抑菌活性研究

为了探讨新合成的s-三唑[3,4-b]-1,3,4-噻二嗪衍生物的抗菌活性,对10种s-三唑[3,4-b]-1,3,4-噻二嗪衍生物进行了抑菌实验测定,对其中4种进行了MIC、生长曲线测定及构效关系的探讨。结果表明,该系列s-三唑[3,4-b]-1,3,4-噻二嗪衍生物对受试菌株均有一定的抑制作用,其中TSQ5、TSQ6、ISO2和ISO3作用较为明显,通过构效关系探讨证实氯取代基起了重要作用。     

玫瑰茄醇提物的抑菌活性及其作用机制

玫瑰茄具有多种药理活性,包括抗肿瘤、抗氧化和抑菌作用等,但目前关于玫瑰茄的抑菌作用研究较少,有关抑菌机制方面的研究尚未见报道. 本文通过测定玫瑰茄醇提物对大肠杆菌和金黄色葡萄球菌细胞膜、蛋白质和核酸的影响,及其与DNA的作用方式等,系统阐述玫瑰茄的抑菌作用机制. 电导率和大分子物质的测定结果显示,玫瑰茄醇提物只对菌体的细胞膜造成微小损伤,其抑菌作用的靶点不在细胞膜. SDS-PAGE和DAPI结果显示,玫瑰茄醇提物可抑制大肠杆菌和金黄色葡萄球菌蛋白质和核酸的合成. 琼脂糖凝胶电泳和紫外吸收光谱结果显示,玫瑰茄醇提物可与DNA结合,当DNA与药物的浓度比较低时,玫瑰茄醇提物与DNA以嵌入结合为主,当二者的浓度较高时,两者间发生的是氢键结合. 上述结果证明,玫瑰茄醇提物对大肠杆菌和金黄色葡萄球菌抑菌机制,主要是药物通过与DNA发生嵌入结合和氢键结合,使DNA不能进行正常的复制和转录,降低核酸的含量,进而影响蛋白质的合成,最终导致菌体生物学功能的丧失.     

s-三唑[3,4-b]-1,3,4-噻二嗪衍生物抑菌活性研究*

为了探讨新合成的s 三唑 [3,4 b] 1 ,3 ,4 噻二嗪衍生物的抗菌活性 ,对 1 0种s 三唑 [3,4 b] 1 ,3,4 噻二嗪衍生物进行了抑菌实验测定 ,对其中 4种进行了MIC、生长曲线测定及构效关系的探讨。结果表明 ,该系列s 三唑 [3 ,4 b] 1 ,3 ,4 噻二嗪衍生物对受试菌株均有一定的抑制作用 ,其中TSQ5、TSQ6、ISO2和ISO3作用较为明显 ,通过构效关系探讨证实氯取代基起了重要作用。     

肉桂不同植物部位精油成分分析及抑菌活性研究

本研究选用肉桂(Cinnamomum cassia)的桂皮、桂叶、桂枝、果实、花萼5种植物部位为研究对象,通过气质联用对各部位精油的主要成分组成进行了分析比较。在此基础上,从抑菌圈、最低抑菌浓度(MIC)、最低杀菌浓度(MBC)等方面比较各部位精油对金黄色葡萄球菌(Staphylococcus aureus)、大肠杆菌(Escherichia coli)抑制活性。结果表明,各部位精油中的主要成分均为反式肉桂醛、邻甲氧基肉桂醛等,但各成分的含量存在明显差异,以花萼中的反式肉桂醛含量最高(87.68%)。各部位精油对两种供试微生物均具有显著抑菌效果,以桂枝中所含精油的抑菌效果最佳,对E.coli和S.aureus的MIC分别为0.05%和0.025%,MBC同样也分别为0.05%和0.025%。     

虫草素的抑菌活性及机理研究

虫草素为蛹虫草等食药保健品的主要活性成分.为进一步评价分析虫草素的抑菌活性及机理,通过最低抑菌浓度及抑菌圈实验测定、扫描电镜观察虫草素对6种常见细菌的抑菌谱及效果,测定供试菌的生长曲线、胞内紫外吸收物质泄露和菌体形态变化,分析虫草素抑制菌体生长及破坏细胞结构机理.结果表明,在溶解度范围内虫草素对3种G+菌有明显抑菌效果...     

氨基酸环状衍生物的合成及抑菌活性

近年来,氨基酸及其衍生物在医药和农业上已显示有广阔的应用前景。现就近十余年来,国外文献报道的具有抗病原微生物活性的氨基酸环状衍生物作一简要概述。     

YD4-6和NV11-4菌株抑菌活性及诱导水稻防御性相关酶活性变化

从麦田和蔬菜地土样中筛选到2株具有较高抗菌活性的生防菌株YD4-6和NV11-4,测定了其抑菌活性和诱导水稻防御性相关酶活性的变化。抑菌活性测定结果表明YD4-6和NV11-4对水稻纹枯病菌、水稻稻瘟病菌、油菜菌核病菌和白菜黑斑病菌均具有较强的抑菌活性。两菌株均不产生几丁质酶活性,但NV11-4能产生纤维素酶活性。针对其对水稻病原菌的抑菌活性和纤维素酶活性的差异及其特性,研究了2个菌株诱导水稻防御性酶活性的变化。结果表明,YD4-6和NV11-4菌株均可有效诱导水稻PPO、POD、PAL、SOD活性增强,MDA含量升高。接种水稻纹枯病菌和使用YD4-6和NV11-4菌株,在使用48 h后,水稻防御酶的活性增加并达到最高,其中NV11-4菌株诱导活性比较持久;YD4-6使用后,诱导水稻的MDA含量增幅较大。结果显示,2个菌株均可有效的诱导水稻防御性酶活性增强和MDA含量增加。经16S rRNA鉴定后,菌株Y4-6确定为蜡质芽孢杆菌,NV11-4确定为枯草芽孢杆菌。     

β-1,3-1,4葡聚糖酶基因克隆表达及其抗菌活性与机理研究进展

β-1,3．1,4-葡聚糖酶是一类能水解β-1,3．糖苷键和β-1,4-糖苷键的酶,因其主要分解大麦中的β-1,3-1,4-葡聚糖和细菌地衣多糖,所以又称地衣多糖酶。综述了β-1,3．1,4-葡聚糖酶基因的克隆表达及其抗菌活性与机理最新研究进展。     

Modification of central metabolic pathway in escherichia coli to reduce acetate accumulation by heterologous expression of the bacillus subtilis acetolactate synthase gene

A novel metabolic engineering technique involving the redirection ofcellular carbon fluxes was employed to reduce acetate production in an Escherichia coli culture. Metabolic engineering was achieved by cloning E. coli the gene for the Bacillus subtilis acetolactate synthase (ALS), an enzyme capable of catalyzing the conversion of pyruvate to nonacidic and less harmful species. The heterologous expression of the ALS catabolic enzyme in Escherichia coli drastically modified the cellular glycolytic fluxes. In particular, acetate excretion, which is a common characteristic of E. coli, as well as a physiological burden, was minimized. The residual acetate level was kept under control and maintained at a level that was below the toxic threshold. The expression of the biologically active ALS enzyme in E. coli did not result in any detectable changes on either cell growth rate or cell yields. The alternative product, acetoin, was shown to be 50 times less harmful than acetate. Similarities in the growth pattern of two different E. coli strains, RR1 and GJT001, under all cultivation conditions suggested that the ability of ALS to reduce acetate accumulation is generic and not strain-specific. (c) 1994 John Wiley & Sons, Inc.     

Use of action spectra for identifying molecular targets and mechanisms of action of solar ultraviolet light

The use of action spectra in the elucidation of the mechanisms of biological action of solar ultraviolet radiation that reaches the surface of the earth is reviewed, and precautions in the preparation and interpretation of such action spectra are discussed. Original experiments are also described which show correlations between lethality and DNA breakage caused by monochromatic solar ultraviolet (UV) wavelengths in Escherichia coli and Bacillus subtilis , which may constitute evidence for an important biological role of DNA breaks leading to lethality in these microorganisms.     

Expression of Escherichia coli Min system in Bacillus subtilis and its effect on cell division

In both rod-shaped Bacillus subtilis and Escherichia coli cells, Min proteins are involved in the regulation of division septa formation. In E. coli , dynamic oscillation of MinCD inhibitory complex and MinE, a topological specificity protein, prevents improper polar septation. However, in B. subtilis no MinE is present and no oscillation of Min proteins can be observed. The function of MinE is substituted by that of an unrelated DivIVA protein, which targets MinCD to division sites and retains them at the cell poles. We inspected cell division when the E. coli Min system was introduced into B. subtilis cells. Expression of these heterologous Min proteins resulted in cell elongation. We demonstrate here that E. coli MinD can partially substitute for the function of its B. subtilis protein counterpart. Moreover, E. coli MinD was observed to have similar helical localization as B. subtilis MinD.     

Multiple xylanases of Cellulomona fimi are encoded by distinct genes

Cellulomonas fimi genomic DNA encoding xylanase activity has been cloned and expressed in Escherichia coli. As judged by DNA hybridization and restriction analysis, twelve xylanase-positive clones carried a minimum of four different xylanase (xyn) genes. The encoded enzymes were devoid of cellulase activity but three of the four bound to Avicel.     

Suppression of the Lethal Effect of Acidic-Phospholipid Deficiency in Escherichia coli by Bacillus subtilis Chromosomal Locus ypoP

An acidic-phospholipid deficiency caused by the pgsA3 allele that encodes a defective phosphatidylglycerophosphate synthase in Escherichia coli is lethal. The only known mutations that suppress this lethality fully have been related to the major outer-membrane lipoprotein. We isolated a Bacillus subtilis chromosomal locus that suppresses the lethality when harbored in a low copy-number plasmid, without restoring the synthase activity or phospholipid composition to normal. The locus was first recognized to suppress the conditional lethality of E. coli YA5512 (pgsA3) that harbored an unidentified mutation(s), allowing its growth in LB medium but not in media of lower osmolarities. The locus was then found to suppress the lethality of pgsA3 in wild-type E. coli W3110. This locus, named ypoP in the database, had 37% nucleotide identity with the E. coli mprA gene, but the amplification of mprA had no suppressive effect. Plasmid pPOP1 containing ypoP completely prevented the decrease in the amount of a porin protein, OmpF, in the outer membrane and also cell mucoidy caused by pgsA3. The mechanisms underlying these unusual effects are discussed in relation to a putative stress signal(s) generated by the acidic-phospholipid deficiency.     

An insertion of Escherichia coli transposable element IS1K into the site immediately before tetracycline-resistance determinant of Bacillus subtilis chromosomal DNA fragment in cloning in E. coli

In cloning in Escherichia coli C600 of a 4.5-kbp HindIII DNA fragment with the tetracycline-resistance determinant (tetBS908) from Bacillus subtilis GSY908 chromosome using a plasmid vector, a 5.2-kbp HindIII DNA fragment was also isolated at a ratio of 2 to 89. The two independently obtained 5.2-kbp fragments were an insertion derivative of the 4.5-kbp fragment and carried E. coli transposable element ISlK, which was inserted at the same site immediately before tetBS908 in the same direction. For the ISlK insertions, the 8-bp sequence CAAATTTT was used as a target, this having no similarity to any published sequences.     

Building the blueprint of life

With recent breakthroughs in experimental microbiology making it possible to synthesize and implant an entire genome to create a living cell, the challenge of constructing a working blueprint for the first truly minimal synthetic organism is more important than ever. Here we review the significant progress made in the design and creation of a minimal organism. We discuss how comparative genomes, gene essentiality data, naturally small genomes, and metabolic modeling are all being applied to produce a catalogue of the biological functions essential for life. We compare the minimal gene sets from three published sources with functions identified in 13 existing gene essentiality datasets. We examine how genome-scale metabolic models have been applied to design a minimal metabolism for growth in simple and complex media. Additionally, we survey the progress of efforts to construct a minimal organism, either through implementation of combinatorial deletions in Bacillus subtilis and Escherichia coli or through the synthesis and implantation of synthetic genomes.