趋磁螺菌AMB-1磁小体合成相关基因的克隆及功能分析

为了更清楚的了解趋磁螺菌产磁小体的合成机理和调节途径,用Tn5转座子诱变的方法筛选得到了2株磁小体合成降低的突变株,并克隆了突变株中被插入失活的基因,分别为编码ABC型Fe3+转移系统中的离子结合蛋白的amb3385基因和功能未知的锄b3672基因.互补实验表明携带amb3385和amb3672基因的广宿主载体可以不同程度地恢复突变株中磁小体的合成,证明了D.schuler关于磁小体合成假说的第一个步骤,即Fe3+从胞外向经由Fe3+转运蛋白运输至了胞内.由于amb3672基因比对时未发现特殊相似基因,其功能尚需进一步研究.     

趋磁细菌的磁小体结构相关蛋白研究进展

趋磁细菌的磁小体由双层脂分子包被,膜上含有很多特异性的可溶和跨膜蛋白,在磁小体基质和颗粒间连接中还存在其他结构相关蛋白.趋磁细菌通过对磁小体膜或结构相关蛋白的遗传调控,实现从铁的吸收、氧化和还原—铁氧化体的沉积和成晶—磁小体链的装配和维护等一系列环节,取得了原核细胞中的最高结构水平之一——膜状细胞器结构.趋磁细菌借助磁小体结构对外界磁场(包括地磁场)信号作出响应亦提供了一个磁感受生物物理机制和地磁生物效应的简单模型.     

一种趋磁弧菌及其磁小体特性的研究

南京城郊一淡水池塘污泥中存在一种弧形趋磁细菌NMV—1,在地磁场作用下一致向北游动,细胞可连接成链状,有2～13个菌体,长达2～10μm,透射电子显微镜(TEM)观察表明每个细胞内含11～15颗磁小体,呈长方体,沿菌体长轴排列成链状,磁小体尺度为:长120nm,宽80nm,处在稳定的单磁畴晶体范围内.能谱分析仪显示该菌磁小体的元素组成为铁(Fe),由晶体衍射分析表明磁小体为单晶结构.NMV—1趋磁弧菌的发现为研究用生物方法制备新型纳米磁性材料提供了必要的基础     

趋磁细菌与磁小体的研究

趋磁细菌是一类能够在一定的磁场内按磁力线方向运动的细菌,菌体内含有磁性颗粒,称磁小体.磁小体具有重要的应用价值.目前,对趋磁细菌的开发和利用主要是在磁性记录材料、分离技术和医疗卫生等方面.     

趋磁细菌与磁小体的研究

趋磁细菌是一类能够在一定的磁场内按磁力线方向运动的细菌,菌体内含有磁性颗粒,称磁小体.磁小体具有重要的应用价值.目前,对趋磁细菌的开发和利用主要是在磁性记录材料、分离技术和医疗卫生等方面.     

—株G~-球形趋磁细菌的发现与表征

在玄武湖水域发现一株 Ｇ－ 球形趋磁细菌 Ｘ Ｗ － １ ,光学显微镜下观察,可见菌体在地磁场的作用下,快速北向游移,平均游动速率约为０ ．１４ ｍ ｍ／ｓ ,该菌株对磁场的作用极其敏感．透射电镜观察显示,在每一菌体的细胞壁上镶嵌了１２ 颗左右的磁小体,磁小体的大小和形状均匀一致,每颗磁小体长约６０ｎ ｍ ,宽４０ｎｍ ,ｘ 射线能谱测试分析表明,磁小体为铁的氧化物．     

趋磁细胞研究：I.武昌东湖水体中趋磁细胞WD—1的分离

武昌东湖水域中存在杆状，螺旋状和旺状等不同形态的趋磁细胞，通常在细胞内有２～１０个数量不等的磁小体，在微好氧条件下利用半固体培养基分离到一株Ｇ＾－，短杆状的趋磁细胞ＷＤ－１，能谱电镜分析表明，该菌磁小体的元素组成是Ｆｅ，Ａｌ，Ｚｎ，Ｇａ，Ｐ和Ｓ，共含量分别占８４，５７％，３．９８％，２．７５％、２．２１％、１．１２％和０．９３％。     

一株G^-球形趋磁细菌的发现与表征

在玄武湖水域发现一株Ｇ＾－球形趋磁细菌ＸＷ－１，光学显微镜下观察，可见菌体在地磁场的作用下游移，平均游离速率久为０．１４ｍｍ／ｓ，该菌对磁场的作用极其敏感，管射电镜观察显示，在第五菌体的细胞直镶嵌了１２颗左右的磁小体，磁小体的大小和形状均匀一致，每颗磁小体长约６０ｎｍ，宽４０ｎｍ，ｘ射线能谱测试分析表明，磁小体为铁的氧化物。     

一种具有磁光性能的潜在药物载体的研制

磁小体是磁靶向给药领域的研究热点,为了精准示踪生物体内的磁小体来指导靶向,基于磁小体和量子点构建一种新型磁光载体.利用静置培养和磁吸附的方法收集富含磁小体的趋磁细菌AMB-1,并通过超声破碎及磁吸附方法提取长度为5~10个的磁小体链,运用点击化学反应将含有羧基的CdTe/CdS量子点修饰到磁小体膜上,并利用人肝癌细胞HepG2初步开展光示踪有效性的验证.结果发现该载体可以成功地被细胞摄取,并在细胞内观测到磁小体的分布.笔者成功地研制出磁光载体,为后续的磁靶向给药、磁靶向热疗及荧光一体化的研究及应用提供了坚实的基础.     

破解趋磁细菌断裂磁小体链的方式

趋磁细菌是在20世纪70年代由理查德·布莱克默（RichardBlakemore）发现的一类在外磁场作用下能作定向运动的细菌。它们体内有一种叫做"磁小体"的物质,其主要成分是Fe₃O₄和Fe₃S₄。众多的磁小体在趋磁细菌体内聚集成链状,使得它们具有趋磁性。趋磁细菌发生细胞分裂时,面临一个很大的挑战:将体内的磁小体链"折断"为两部分。因为如果像正常的细胞分裂方式一样,那么,从趋磁细菌分裂开始到最终形成两个子细胞的力是不足以断开磁小体链的。     

Functional analysis of hydrogenases and their effects on cell growth and magnetosome synthesis in <Emphasis Type="Italic">Magnetospirillum gryphiswaldense</Emphasis>

This study addressed the effect of hydrogen metabolism on cell growth and magnetosome synthesis in Magnetospirillum gryphiswaldense strain MSR-1. Two deletion mutants were generated: L206, with single deletion of the hupL gene encoding H2-uptake [NiFe] hydrogenase; and B206, with double deletion of the hyaB gene encoding H2-producing [NiFe] hydrogenase and the hupL gene. The wild-type and mutant strains were compared in terms of hydrogen uptake capability, hydrogen yield, growth rate, and iron uptake, and o...     

Biomineralization and magnetism of bacterial magnetosomes

Magnetosomes of magnetotactic bacteria are of great interest in understanding biomiueralizatiou and possible links between organisms and geomagnetic field. Fossil maguetosomes are ubiquitous in marine and lake sediments and may significantly contribute to magnetic signals. In this review, we firstly introduce some characteristics of magnetotactic bacteria, followed by considering recent progress in maguetosome formation, magnetic measurements, and identification of bacterial magnetites in bulk sediments as well as their paleoenviroumeutal implications. Finally, we briefly discuss potential future breakthroughs in magnetosome studies and its applications.     

The secretion of lecithinase of Pseudomonas alcaligenes S2 was via type II secretion pathway

Phosphorus is one of the major essential macronutrients for virtually metabolic processes in plant growth and de-velopment[1]. This creates a paradox with major agro-nomic implications since the phosphate form of phospho-rus is one of the least soluble mineral nutrient ions in the soil. The concentration of soluble phosphorus in soil is usually very low, normally at levels of 1 ppm or less (10 mol/L H2PO4?). Mineral forms of phosphorus are repre-sented in soil by primary minerals, such as ap…     

Regulation of eight avr genes by hrpG and hrpX in Xanthomonas campestris pv. campestris and their role in pathogenicity

Eight putative avirulence genes in Xanthomonas campestris pv. campestris (Xcc) strain 8004 were characterized by Tn5gusA5 mutagenesis and gene expression analysis. The virulence test of mutants on Chinese radish showed that all mutants in individual avr genes except avrBs2 mutant were not significantly different from the wild type in virulence. The avrBs2 mutant showed reduced virulence and bacterial growth in planta. Gene expression analysis using β-glucuronidase as reporter indicated that avrBs1.1，avrBs1，avrXccB，avrXccC，avrXccE1 were regulated by hrpG, whereas avrXccA1, avrXccA2 and avrBs2 were not. RT-PCR analysis showed that all hrpG-regulated genes except avrBs1 were also regulated by hrpX. In addition, it was demonstrated that avrBs1　 was responsible for elicitation of a type III dependent hypersensitive reaction (HR) on nonhost plant pepper ECW-10R, and wild type Xcc 8004 was unable to cause HR on pepper ECW-20R.     

电磁能在人体不同组织中的积蓄及其影响因素

该文从经典电动力学的玻印廷矢量和麦克斯韦场方程推导出了人体组织比吸收率的一般表达式 ,根据表达式中三个基本的复数电磁参量在不同生物组织、不同频率下的可能取值 ,讨论了三个复数电磁参量对生物组织比吸收率的影响。结果表明 ,在非磁性组织中 ,当f<0 .5GHz时 ,电磁损耗主要是组织电导率决定的 ;当f>0 .5GHz时 ,随频率升高介电损耗变得更为重要。某些人体组织 (如脑组织 )中含有微小的磁性物质 ,通过估算发现这些磁性体的比吸收率是周围非磁性组织的 4 0 0多倍。     

基于转座子策略提高链霉菌中landomycin E产量的研究

【目的】对影响放线菌链霉菌Streptomyces globisporus产landomycin E(laE)的代谢网络进行研究,以提高次生代谢物的产量。【方法】通过构建含强启动子和抗性标记的转座子Tn7为基础的转座子,整合至S.globisporus的染色体产生突变库,筛选高产量的突变株并对其代谢网络进行研究分析。【结果】利用构建好的Tn7-转座子连续转化链霉菌S.globisporus,经过数轮的突变和筛选,得到6株产量有较大改变的突变株,对整合位点的亚克隆和测序结果表明,该位点整合导致编码类似细菌的某些调节因子如TetR和GntR家族的蛋白的基因失活。【结论】所构建的经过修饰的微型Tn7-转座子不仅带有抗性标记且有启动子,可插入链霉菌染色体产生突变,进而提高次生代谢物laE的产量,同时也证明,转座子基载体可应用于非模式菌链霉菌。     

The secretion of lecithinase of Pseudomonas alcaligenes S2 was via type Ⅱ secretion pathway

Strain S2 is a lecithin （or phosphatidylcholine）- solubilizing bacterium, which was isolated from the rice rhizosphere in rural areas of Beijing, China. On the basis of a polyphasic study involving phenotypic tests, physiological and biochemical tests, 16S rDNA sequence analysis, G＋C content determination and DNA-DNA hybridizations analysis, strain S2 was identified as Pseudomonas alcaligenes. R alcaligenes S2 was mutagenized with Tn5 and four mutants showing decreased or increased solubilizing ability of lecithin were isolated based on the halo size around colonies on the solid plate supplemented with egg yolk. To characterize the genes of R alcaligenes S2 involved in solubilization of lecithin, the EcoR I fragments of the chromosomes from the four mutant strains carrying a single transposon were cloned, and the DNA sequences flanking the Tn5 were determined. The Tn5 insertion sites in the mutants M808, M1329 and M1400, showing decreased solubilizing ability of lecithin, were found to be located in the xcpS, xcpX and xcpW , respectively, whose products XcpS, XcpX and XcpW were the components of type Ⅱ secretion pathway. Complementation of xcpS, xcpX and xcpW could restore the corresponding mutants M808, M1329 and M1400 to solubilize lecithin. The data suggested that mutation in one of these xcp genes would lead to the absence of mature lecithinase secretion into the extracellular medium. The data also indicated that the secretion of lecithin-hydrolyzing enzyme of R alcaligenes was via type Ⅱ secretion pathway. In the mutant M20 showing increasing lecithin-hydrolyzing activity, the interrupted gene showed 86% identity with chpA of Pseudomonas aeruginosa PAO1, whose product plays an important role in controlling twitching motility of the bacterial ceils.