An acidic protein aligns magnetosomes along a filamentous structure in magnetotactic bacteria

Magnetotactic bacteria are widespread aquatic microorganisms that use unique intracellular organelles to navigate along the Earth's magnetic field. These organelles, called magnetosomes, consist of membrane-enclosed magnetite crystals that are thought to help to direct bacterial swimming towards growth-favouring microoxic zones at the bottom of natural waters. Questions in the study of magnetosome formation include understanding the factors governing the size and redox-controlled synthesis of the nano-sized magnetosomes and their assembly into a regular chain in order to achieve the maximum possible magnetic moment, against the physical tendency of magnetosome agglomeration. A deeper understanding of these mechanisms is expected from studying the genes present in the identified chromosomal 'magnetosome island', for which the connection with magnetosome synthesis has become evident. Here we use gene deletion in Magnetospirillum gryphiswaldense to show that magnetosome alignment is coupled to the presence of the mamJ gene product. MamJ is an acidic protein associated with a novel filamentous structure, as revealed by fluorescence microscopy and cryo-electron tomography. We suggest a mechanism in which MamJ interacts with the magnetosome surface as well as with a cytoskeleton-like structure. According to our hypothesis, magnetosome architecture represents one of the highest structural levels achieved in prokaryotic cells.     

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.     

地磁场与生物的磁效应

对地磁场研究历史及其发展趋势作了简要的论述,提出地磁场强度是认识地球深部动力学过程的有效途径之一。同时,对生物的磁效应,特别是趋磁细菌的研究历史、现状及其在地球科学和生命科学中的潜在应用作了分析,这对不同学科的交叉与渗透具有一定的促进作用。     

核电厂应急准备的代价利益分析

简要介绍了核电厂应急计划区的划分方法和国际上先进堆应急计划的安全要求;阐述了应急准备代价利益分析的原则思想,并介绍了构建的分析模型;最后给出了应急准备代价和利益比较的结果。     

A comparative study of magnetic properties between whole cells and isolated magnetosomes of <Emphasis Type="Italic">Magnetospirillum magneticum</Emphasis> AMB-1

The magnetic properties of magnetosome magnetite are of interdisciplinary interest because magnetosomes are potential carriers of natural remanent magnetization and paleoenvironment, as well as novel nano-biomaterials in biotechnological and biomedical applications. We carried out magnetic and electron transmission microscopy analyses of fresh Magnetospirillum magneticum AMB-1 whole cells and isolated magnetosomes. Results revealed that AMB-1 synthesized single-domain magnetite magneto-somes, which are arra...     

趋磁螺菌AMB-l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amb3672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.Schüler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.     

氧化亚铁硫杆菌中磁小体形成相关基因mpsA在不同铁源刺激下的差异表达

为研究氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)在胞内形成的电子致密的磁性颗粒的相关基因,对氧化亚铁硫杆菌标准菌株ATCC23270的全基因组的生物信息学进行分析,在ATCC23270的全基因组上查找与趋磁细菌中mpsA基因的同源基因ORF1622,并对其进行保守结构域、氨基酸序列比对以及蛋白质同源性分析.利用反转录PCR技术从转录水平研究mpsA基因在硫培养条件下分别用20 mmol/L FeCl_3和FeSO_4·7H_2O刺激时的差异表达以验证它们在磁小体形成过程中的作用.研究结果表明:ORF1622编码的蛋白含有PRK05724结构域,与mpsA序列相同度为48%,与acetyl-CoA carboxylase carboxyltransferase subunit alpha同源;氧化亚铁硫杆菌中的mpsA基冈在转录层面的表达与亚铁有直接关系,并且氧化亚铁硫杆菌仅在亚铁培养下生成磁小体,因此,它与氧化亚铁硫杆菌中磁小体的形成相关.     

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。     

Biological sensing of small field differences by magnetically sensitive chemical reactions

There is evidence that animals can detect small changes in the Earth's magnetic field by two distinct mechanisms, one using the mineral magnetite as the primary sensor and one using magnetically sensitive chemical reactions. Magnetite responds by physically twisting, or even reorienting the whole organism in the case of some bacteria, but the magnetic dipoles of individual molecules are too small to respond in the same way. Here we assess whether reactions whose rates are affected by the orientation of reactants in magnetic fields could form the basis of a biological compass. We use a general model, incorporating biological components and design criteria, to calculate realistic constraints for such a compass. This model compares a chemical signal produced owing to magnetic field effects with stochastic noise and with changes due to physiological temperature variation. Our analysis shows that a chemically based biological compass is feasible with its size, for any given detection limit, being dependent on the magnetic sensitivity of the rate constant of the chemical reaction.     

DMTB: A comprehensive online resource of 16S rRNA genes,ecological metadata,oligonucleotides, and magnetic properties of magnetotactic bacteria

Magnetotactic bacteria (MTB) are of interest in microbiology, biomineralization, advanced magnetic materials, and bio-geo-sciences because of their ability to form highly ordered intracellular magnetic minerals. Great strides for MTB studies have been made in the past four decades. In this paper we complied the first internet-accessible database for MTB, Database of Magnestotactic Bacteria (DMTB). It contains information of 16S rRNA gene sequences, corresponding ecological metadata, oligonucleotides, and magnetic properties of MTB. The comprehensive information contained in DMTB will provide a very useful data resource for researchers from different disciplines. The website of DMTB is at http://database.biomnsl.com/.     

—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．     

茚三酮比色法测定磁性载体固定微生物含量的研究

研究利用磁性载体固定微生物处理废水的效果,首先必须测定载体表面固定微生物的含量.通过采用茚三酮比色法来间接测定微生物的含量,确定了该方法的最佳吸收波长、最佳消解时间和冷却时间、缓冲溶液的最佳pH值.研究表明在最佳条件下,细菌裂解液显色反应的吸光值与细菌含量呈显著的正相关.     

Occurrence of magnetic bacteria in soil

Enrichment of the ferrimagnetic minerals magnetite and maghemite is frequently observed in the top layer of soil horizons. Although both inorganic and organic processes are known to produce magnetite, magnetite in soils has been ascribed to an inorganic origin. We report here the discovery of living magnetic bacteria, similar to those found in salt- and fresh-water sediments, in the A horizon of a well developed soil profile in a typical meadow environment in southern Bavaria. The bacteria were detected in fresh samples using an optical microscope equipped with a rotating magnetic field and a volumetrically calibrated depression slide, permitting accurate counts of the volume density of the organisms. We suggest that magnetic bacteria and their magnetofossils can contribute to the magnetic properties of soils.     

大梯度磁滤器滤速对除饮用水微污染的影响

简要介绍了大梯度磁滤器除饮用水微污染第一阶段实验中滤速对处理效果的影响情况．结合原水水质以L湖水作为处理原水，采用该工艺确定最佳滤速范围，试验说明该工艺对水中浊度、色度、有机物、细菌、大肠杆菌及藻类等的去除具有很好效果．     

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.     

单畴磁铁矿磁接收器磁学模型

很多生物可以利用地磁场辨别方向和方位,而生物磁铁矿被广泛发现存在于这些生物体中,研究者认为,生物磁铁矿与周围组织(包括神经组织)构成磁接收器,它在与外界磁场的相互作用中,将外界磁场信息转化成神经信息促使生物作出相应的反应;生物磁铁矿磁接收器理论包括单畴磁铁矿磁接收器模型和超顺磁磁铁矿磁接收器模型;趋磁细菌体内存在典型的单畴磁铁矿颗粒,本文中,以趋磁细菌为例,从磁学理论角度出发,定性的探讨了单畴磁铁矿磁接收器的磁学模型和工作机制:在外磁场中,外面包围着生物膜的单畴晶体会受到力的作用,单畴晶体把力转加给生物膜,再被生物膜中的机械感受器接收到,再转变为刺激信号,引起细胞相应的运动行为;或者是,磁铁矿粒子通过与生物膜的结合,把受到的力转变为打开或关闭离子通道,影响离子的流入,跨膜电势发生改变,从而产生刺激信号;多个单畴晶体及膜的存在会导致信号的增加与放大.     

污水处理中的若干磁化生物效应研究

运用磁场对生活废水进行磁化处理并观察其生物效应.对磁化杀菌作用、好氧生物活性变化和藻类生长促进作用等进行了试验测定.结果表明,磁化处理对污水中的细菌具有较强的杀菌作用;当磁场强度达到3500 GS时,好氧生物活性增加18%;与未磁化污水比较,磁化水藻类初级生产力可以提高1倍.本文还进一步分析探讨了其生物效应机制.     

基于磁弛豫原理的磁化学传感器研究进展

基于磁性纳米粒子的磁化学传感器是集纳米/微米技术、化学反应、生物技术及核磁共振技术于一体的多学科交叉、多技术集成的传感器.利用这一传感器可以检测各种金属离子、蛋白质、小分子、细菌、病毒、DNA、分子间的相互作用、细胞、肿瘤以及癌症.首先简要概述磁化学传感器的传感原理,然后重点介绍在检测方面的应用.     

生物体内纳米磁性矿物质（Fe3O4）的磁畴结构研究

分析了磁铁矿粒子的单畴临界尺寸，表明生物体内的纳米磁铁矿粒子具有单畴特性。分别讨论了石鳖、趋磁细菌及蜜蜂体内纳米磁铁矿粒子的磁畴结构及磁矩分布，探讨了与地磁场相互作用下它们的生物导航功能机制。     

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...