革兰氏阳性菌荚膜多糖研究进展*

细菌的荚膜多糖是生物膜的重要组成部分,在细菌的生长分裂、维持细胞壁形态、抵御外界环境以及免疫反应等方面都起到重要作用。在致病菌中,荚膜多糖常作为一种毒力因子发挥作用。在革兰氏阳性菌中,荚膜多糖的化学结构、生物合成过程及功能应用越来越受到关注。讨论了革兰氏阳性菌中部分致病菌的荚膜多糖与非致病菌表面多糖的分布位置、化学组成及其结构特异性。重点讨论三种具有代表性的革兰氏阳性致病菌及非致病菌株:肺炎链球菌(Streptococcus pneumonia)、金黄色葡萄球菌(Staphylococcus aureus)及乳酸乳球菌(Lactococcus lactis)。综述革兰氏阳性菌中荚膜多糖生物合成的三种方式:Wzx/Wzy-依赖通路、ABC转运蛋白(ABC transporter)途径及合酶依赖途径,并举例解释了相应多糖的合成过程及相关基因。介绍了革兰氏阳性菌荚膜多糖及表面多糖的生理功能,如屏障保护功能、胞间黏附功能以及参与宿主细胞的免疫反应等。结合荚膜多糖的生物学功能,概述其当前主要研究进展,如构建高耐受工程菌疫苗研制等。结合细菌荚膜多糖的特征差异,对其在医药与工业生产领域的广阔前景提出展望和建议。     

革兰氏阴性菌脂蛋白Lol系统转运蛋白的功能及表面展示分泌机制

细菌脂蛋白是细胞膜的重要组成成分,在革兰氏阴性菌的生理及致病性中扮演着重要的角色。革兰氏阴性菌中已知负责胞内脂蛋白转运的是Lol(Localization of lipoprotein)系统。该系统识别成熟脂蛋白的分泌信号,将外膜脂蛋白转运并定位于细胞外膜内侧。近年来的研究发现,跨细胞外膜进行表面展示的脂蛋白实际上在革兰氏阴性菌中广泛存在,其分泌机制开始成为研究热点。为了对革兰氏阴性菌中脂蛋白分泌机制的研究现状有一个系统全面的了解,本文概述了脂蛋白转运过程中Lol系统5个转运蛋白的功能与保守性、不同细菌中脂蛋白分泌信号的差异以及表面展示脂蛋白可能的分泌机制。     

内陆土壤冷适应细菌的筛选分类与细胞膜脂肪酸的适冷机制

嗜冷菌及耐冷菌是冷适应酶及生物活性物质的重要资源。本研究从内陆土壤筛得33株冷适应细菌,包括6株革兰氏阳性菌与27株革兰氏阴性菌。通过细胞膜脂肪酸分析表明,革兰氏阳性菌的膜脂肪酸主要为分支脂肪酸,推测分支结构是阳性菌膜脂的主要适冷机制。革兰氏阴性菌呈现了不饱和、分支、短链等多样的膜脂适冷调节方式。根据脂肪酸组分的多样性,选择并鉴定了17株嗜冷及耐冷菌分布在11个属中,细胞膜脂肪酸组成的变化规律与细菌16SrRNA的进化分布高度一致。研究还表明同为不饱和脂肪酸为主的革兰氏阴性菌呈现了不同的适冷机理。相关研究不仅阐述了冷适应细菌的细胞膜脂肪酸的适应机制,而且为相关适冷酶源的开发利用提供了宝贵的资源。     

链球菌脂蛋白的功能作用及其作为疫苗候选蛋白和抗菌药物靶标的研究进展

脂蛋白是一类广泛存在于革兰氏阴性细菌和革兰氏阳性细菌中的细胞膜锚定蛋白,具有多种生物学功能.脂蛋白不仅作为细菌的毒力因子,而且能够识别和激活宿主的免疫系统,是当前预防和治疗细菌感染的热门靶点之一,本文对链球菌中脂蛋白的主要功能及其在疫苗和抗菌药物研究中的进展进行了综述和展望,为今后链球菌中脂蛋白的深入研究拓宽了思路.     

革兰氏阳性菌群体感应系统研究进展

细菌利用群体感应系统进行细菌间以及细菌与宿主间的交流,革兰氏阳性与阴性菌的群体感应系统差异显著,阳性菌的群体感应系统主要由寡肽类信号分子和受体蛋白组成,对细菌致病性等相关生理特性具有重要作用。就常见的革兰氏阳性菌：蜡样芽孢杆菌、枯草芽孢杆菌、金黄色葡萄球菌和肺炎链球菌的群体感应系统的基因组成、信号分子及其调控机制特点的研究进行了总结,对群体感应系统在细菌营养吸收、生物膜形成、毒力因子和孢子产生等重要生理活动的调节机制进行了重点阐述,为革兰氏阳性菌群体感应的相关研究提供了有益参考。     

各种革兰氏阳性菌脂磷壁酸特异单克隆抗体的特性

<正>脂磷壁酸(LTAs)存在于许多革兰氏阳性菌的细胞膜上。它是一类由甘油磷酸(PGP)和糖脂组成的聚合体,PGP是LTA的骨架结构,它是各种革兰氏阳性菌共同抗原决定簇。测定某一细菌中交叉反应抗原,依赖于能同异嗜性(heterohile)PGP起反应的抗血清之有效性。     

林可霉素生物合成的研究进展

林可霉素是林可链霉菌(Streptomyces lincolnensis)产生的林可酰胺类抗生素,它抑制细菌细胞的蛋白质合成,临床上主要用于治疗革兰氏阳性菌引起的感染性疾病。林可霉素生物合成基因簇已被克隆和测序。近年来,围绕林可酰胺和丙基脯氨酸的生物合成、调控等进行了深入研究,其硫化反应取得了突破性成果,本文综述了林可霉素生物合成的新进展。     

细菌的中体

中体是细菌内唯一的细胞内膜结构。它是由细胞膜向细胞质内陷而形成的囊状或管状膜结构(图1)。自从1957年从分枝杆菌属(Mycobacterium)的超薄切片中发现其片状的内膜结构以来,陆续在许多革兰氏阳性菌(G~+)和一部分革兰氏阴性菌(G~-)中发现有此结构。     

筛选产类细菌素乳酸菌及类细菌素特性研究

从健康鸡肠道内容物及新鲜粪便中分离到21株乳酸菌,通过单层琼脂平板扩散实验,筛选出1株对藤黄微球菌(Micrococcus luteus)、金黄色葡萄球菌(Staphylococcus aureus)和枯草杆菌(Bacillus subtilis)等革兰氏阳性菌和大肠杆菌(Escherichia coli)等革兰氏阴性菌有明显抑菌活性代谢产物的乳酸菌,经细菌鉴定为乳杆菌属。排除酸和过氧化氢的干扰后,发酵液上清对指示菌仍有抑菌活性;用胰蛋白酶和蛋白酶K处理后抑菌活性明显降低,而胃蛋白酶对其活性无影响;用过氧化氢酶作用上清液,抑菌效果不变,说明过氧化氢未起作用;pH在2.0~7.0时,发酵上清液有抑菌活性;培养液粗提物经120℃处理20 min仍有部分活性,表明培养上清中有蛋白质类细菌素。     

二硫吡咯酮类抗生素的生物合成与代谢工程应用北大核心CSCD

二硫吡咯酮类抗生素是一类具有独特的吡咯酮二硫杂环戊二烯(4H-[1,2]二硫[4,3-b]吡咯-5-酮)骨架的化合物的总称。基于N-7位酰基侧链的不同以及N-4位是否含有甲基,可分为N-methyl-Nacylpyrrothine、N-acylpyrrothine和thiomarinols等类别。迄今为止,已有27种该类化合物被报道,重要代表包括全霉素(holomycin)、硫藤黄菌素(thiolutin)、金霉素(aureothricin)以及最近发现的thiomarinols。就生物活性而言,二硫吡咯酮类抗生素具有广谱的抗细菌活性,对多种微生物,包括革兰氏阴性菌、革兰氏阳性菌以及寄生虫都有较好的杀灭活性。甚至一些二硫吡咯酮衍生物表现出较强的抗肿瘤活性。近几年来,多个二硫吡咯酮类抗生素的生物合成基因簇相继被报道,其生物合成机理也逐步被阐明。本文将针对目前国内外二硫吡咯酮类抗生素的生物合成研究进展,以及在组合生物合成与代谢工程领域所取得的成果进行综述,旨在为通过合成生物学的方法创造结构新颖、高效低毒的"非天然"二硫吡咯酮类化合物提供理论借鉴。     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

Comparative morphology of the carpel in the Liliaceae: Hewardieae, Petrosavieae, and Tricyrteae

The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.     

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.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.     

Chemical constituents from the fruits of Rhus typhina L. and their chemotaxonomic significance

This work describes the isolation and characterization of twenty-nine compounds from the fruits of Rhus typhina L., including eleven flavonoids (1–11), eleven phenols (12–22), two pentacyclic triterpenes (23–24), two organic acids (25–26), one lumichrome (27), one courmarin (28) and one pyrimidine (29) on the basis of their spectroscopic data. Compounds apigenin (1), daidzein (4), orobol (5), 3′, 5, 5′, 7-tetrahydroxyflavanone (6), naringenin (7), butein (8), (-)-catechin (9), quercetin-3-O-α-L-(3″-O-galloyl)-rhamnoside (11), 2-hydroxybenzoic acid (13), 4-hydroxybenzaldehyde (14), vanillin (15), methyl 3,4-dihydroxybenzoate (16), 3,5-dihydroxybenzamide (18), tyrosol (19), caffeic acid (20), 3-(2,4,6-trihydroxyphenyl)-1-(4-hydroxyphenyl)-propan-1-one (21), phlorizin (22), friedelin (23), oleanolic acid (24), 4,4-dimethyl-heptanedioic acid (25), anthranilic acid (26), lumichrome (27), scoparone (28) and uracil (29) have not been recorded before in this plant. This is the first report on the occurrence of compounds 4–7, 9, 11, 13–14, 16, 18–21, 25–29 from the genus Rhus. Moreover, the chemotaxonomic significance of these isolated compounds was also summarized.