磁分离仪分离磁性细菌的新方法

磁性细菌胞内可以产生磁性颗粒,因此具有趋磁性,基于这种特性,利用磁分离的原理,本研究开发了一种磁性细菌分离仪,提供了一种分离磁性细菌的新方法。以氧化亚铁硫杆菌为例,使用磁性细菌分离仪进行分离,可以得到强磁菌和弱磁菌。利用透射电镜观察,强磁菌胞内磁性颗粒明显多于弱磁菌;半固体平板磁泳实验也表明强磁菌趋磁性明显强于弱磁菌。各项实验结果表明磁性细菌分离仪可以有效地分离磁性细菌,这是一种分离磁性细菌的新方法,将促进磁性细菌分离培养的研究。     

Quantifying the magnetic advantage in magnetotaxis

Magnetotactic bacteria are characterized by the production of magnetosomes, nanoscale particles of lipid bilayer encapsulated magnetite, that act to orient the bacteria in magnetic fields. These magnetosomes allow magneto-aerotaxis, which is the motion of the bacteria along a magnetic field and toward preferred concentrations of oxygen. Magneto-aerotaxis has been shown to direct the motion of these bacteria downward toward sediments and microaerobic environments favorable for growth. Herein, we compare the magneto-aerotaxis of wild-type, magnetic Magnetospirillum magneticum AMB-1 with a nonmagnetic mutant we have engineered. Using an applied magnetic field and an advancing oxygen gradient, we have quantified the magnetic advantage in magneto-aerotaxis as a more rapid migration to preferred oxygen levels. Magnetic, wild-type cells swimming in an applied magnetic field more quickly migrate away from the advancing oxygen than either wild-type cells in a zero field or the nonmagnetic cells in any field. We find that the responses of the magnetic and mutant strains are well described by a relatively simple analytical model, an analysis of which indicates that the key benefit of magnetotaxis is an enhancement of a bacterium's ability to detect oxygen, not an increase in its average speed moving away from high oxygen concentrations.     

趋磁细菌运动特性的研究进展

细菌的运动性是影响其生存及致病的一个关键条件,同时也为合成和开发仿生运动体、微型机器人等提供了有效的模型.趋磁细菌具有胞内磁小体从而能够感知磁场的变化,进而影响其运动行为.目前,这种外部磁场与生物体的远程响应模式已在环境、医疗、材料等领域有广泛应用.因此,聚焦于趋磁细菌的运动特性,综述了趋磁细菌运动行为的表征、运动机理...     

趋磁细菌及其应用于生物导航的研究进展

趋磁性细菌是一种由于体内含有对磁场具有敏感性的磁小体,而能够沿着磁力线运动的特殊细菌,本文综述了趋磁细菌的分布、分类、特性、磁小体研究以及趋磁细菌在生物导航方面的研究进展。     

趋磁细菌及其应用于生物导航的研究进展

趋磁性细菌是一种由于体内含有对磁场具有敏感性的磁小体,而能够沿着磁力线运动的特殊细菌,本文综述了趋磁细菌的分布、分类、特性、磁小体研究以及趋磁细菌在生物导航方面的研究进展.     

Effect of super high magnetic field on the growth ofEscherichia coli

Summary Auxotrophic mutants ofEscherichia coli were grown under the super high magnetic field (11.7 Tesla) and the effect of the field both on the growth and mutation frequency of the bacteria was investigated. When the bacteria were cultivated in complex media, the growth was stimulated under 11.7T in comparison with that in geomagnetic field. When the bacteria were grown in synthetic media, the growth rates were reduced significantly. Neither mutagenic nor lethal effects of the magnetic field on the bacteria was observed. A potential application of high magnetic strength as a controlling factor of the bacterial growth was implied.     

A new study of bacterial motion: superconducting quantum interference device microscopy of magnetotactic bacteria.

The recently developed "microscope" based on a high-Tc dc SQUID (superconducting quantum interference device) is used to detect the magnetic fields produced by the motion of magnetotactic bacteria, which have permanent dipole moments. The bacteria, in growth medium at room temperature, can be brought to within 15 micron of a SQUID at liquid nitrogen temperature. Measurements are performed on both motile and nonmotile bacteria. In the nonmotile case, we obtain the power spectrum of the magnetic field noise produced by the rotational Brownian motion of the ensemble of bacteria. Furthermore, we measure the time-dependent field produced by the ensemble in response to an applied uniform magnetic field. In the motile case, we obtain the magnetic field power spectra produced by the swimming bacteria. Combined, these measurements determine the average rotational drag coefficient, magnetic moment, and the frequency and amplitude of the vibrational and rotational modes of the bacteria in a unified set of measurements. In addition, the microscope can easily resolve the motion of a single bacterium. This technique can be extended to any cell to which a magnetic tag can be attached.     

Unusual swimming behavior of a magnetotactic bacterium

Magnetotactic bacteria of strain Mar 1–83, when swimming in an applied magnetic field, did not move as a homogeneous cell suspension, but aggregated in distinct wave-like structures. The waves remained stable during forward movement. The number of cells per wave ranged from a few cells in permanent lateral contact to hundreds of bacteria moving visibly within a wave. Wave formation required a horizontal and vertical magnetic component. Electron microscopy indicated at least 3 distinct parallel chains of magnetosomes inside the bacterium. The cellular magnetic dipole moment was determined. Cell-to-cell magnetic interaction could be ruled out as the sole mechanism that induced wave formation and kept waves stable. Other mechanisms are discussed.     

Magnetic susceptibility of microorganisms.

Total magnetic susceptibility of 13 species and varieties of bacteria was investigated using the relative method of Guy. It has been established that the index of magnetic susceptibility is a constant characteristic of bacteria. Total magnetic susceptibility ranged from --0.3295.10(-6) in Escherichia P678 to --0.4965.10(-6) in Proteus. It has also been established that magnetic susceptibility changes during long-term passages of bacteria in fluctuating +/- 0.1 Oe) magnetic field. This is suggestive of a low threshold of their magnetic susceptibility and permits a rough assessment of the importance of fluctuations of the geomagnetic field for the viability of microbes.     

Various effects on transposition activity and survival of Escherichia coli cells due to different ELF-MF signals

Previous assays with weak sinusoidal magnetic fields (SMF) have shown that bacteria that had been exposed to a 50 Hz magnetic field (0.1–1 mT) gave colonies with significantly lower transposition activity as compared to sham-exposed bacteria. These experiments have now been extended by using a pulsed-square wave magnetic field (PMF) and, unexpectedly, it was found that bacteria exposed to PMF showed a higher transposition activity compared to the controls. The increase of the transposition activity was positively correlated with the intensity of the magnetic fields (linear dose-effect relation). This phenomenon was not affected by any bacterial cell proliferation, since no significant difference was observed in number and size of PMF-exposed and sham-exposed colonies. In addition, the cell viability of E. coli was significantly higher than that of the controls when exposed to SMF, and lower than that of the controls when exposed to PMF. Under our experimental conditions it was shown that exposure to PMF stimulates the transposition activity and reduces cell viability of bacteria, whereas exposure to SMF reduces the transposition mobility and enhances cell viability. These results suggest that the biological effects of magnetic fields may critically depend on the physical characteristics of the magnetic signal, in particular the wave shape.     

Development of Cellular Magnetic Dipoles in Magnetotactic Bacteria

Magnetotactic bacteria benefit from their ability to form cellular magnetic dipoles by assembling stable single-domain ferromagnetic particles in chains as a means to navigate along Earth's magnetic field lines on their way to favorable habitats. We studied the assembly of nanosized membrane-encapsulated magnetite particles (magnetosomes) by ferromagnetic resonance spectroscopy using Magnetospirillum gryphiswaldense cultured in a time-resolved experimental setting. The spectroscopic data show that 1), magnetic particle growth is not synchronized; 2), the increase in particle numbers is insufficient to build up cellular magnetic dipoles; and 3), dipoles of assembled magnetosome blocks occur when the first magnetite particles reach a stable single-domain state. These stable single-domain particles can act as magnetic docks to stabilize the remaining and/or newly nucleated superparamagnetic particles in their adjacencies. We postulate that docking is a key mechanism for building the functional cellular magnetic dipole, which in turn is required for magnetotaxis in bacteria.     

Magnetosome chain superstructure in uncultured magnetotactic bacteria

Magnetotactic bacteria produce magnetosomes, which are magnetic particles enveloped by biological membranes, in a highly controlled mineralization process. Magnetosomes are used to navigate in magnetic fields by a phenomenon called magnetotaxis. Two levels of organization and control are recognized in magnetosomes. First, magnetotactic bacteria create a spatially distinct environment within vesicles defined by their membranes. In the vesicles, the bacteria control the size, composition and purity of the mineral content of the magnetic particles. Unique crystal morphologies are produced in magnetosomes as a consequence of this bacterial control. Second, magnetotactic bacteria organize the magnetosomes in chains within the cell body. It has been shown in a particular case that the chains are positioned within the cell body in specific locations defined by filamentous cytoskeleton elements. Here, we describe an additional level of organization of the magnetosome chains in uncultured magnetotactic cocci found in marine and freshwater sediments. Electron microscopy analysis of the magnetosome chains using a goniometer showed that the magnetic crystals in both types of bacteria are not oriented at random along the crystal chain. Instead, the magnetosomes have specific orientations relative to the other magnetosomes in the chain. Each crystal is rotated either 60°, 180° or 300° relative to their neighbors along the chain axis, causing the overlapping of the (1?1?1) and [Formula in text] capping faces of neighboring crystals. We suggest that genetic determinants that are not present or active in bacteria with magnetosomes randomly rotated within a chain must be present in bacteria that organize magnetosomes so precisely. This particular organization may also be used as an indicative biosignature of magnetosomes in the study of magnetofossils in the cases where this symmetry is observed.     

Use of magnetic particles isolated from magnetotactic bacteria for enzyme immobilization

Summary We report the novel use of magnetic particles isolated from magnetotactic bacteria. Magnetotactic bacteria were collected from enriched sludge by use of a magnetic harvesting apparatus. Magnetic particles separated from magnetotactic bacteria were shown to be pure magnetite. Glucose oxidase and uricase were immobilized on magnetic particles. The activity of glucose oxidase immobilized on biogenic magnetites was 40 times that immobilized on artificial magnetites or Zn-ferrite particles. Both glucose oxidase and uricase coupled with biogenic magnetic particles retained their activities when they were reused 5 times.     

Reduced Efficiency of Magnetotaxis in Magnetotactic Coccoid Bacteria in Higher than Geomagnetic Fields

Magnetotactic bacteria are microorganisms that orient and migrate along magnetic field lines. The classical model of polar magnetotaxis predicts that the field-parallel migration velocity of magnetotactic bacteria increases monotonically with the strength of an applied magnetic field. We here test this model experimentally on magnetotactic coccoid bacteria that swim along helical trajectories. It turns out that the contribution of the field-parallel migration velocity decreases with increasing field strength from 0.1 to 1.5 mT. This unexpected observation can be explained and reproduced in a mathematical model under the assumption that the magnetosome chain is inclined with respect to the flagellar propulsion axis. The magnetic disadvantage, however, becomes apparent only in stronger than geomagnetic fields, which suggests that magnetotaxis is optimized under geomagnetic field conditions. It is therefore not beneficial for these bacteria to increase their intracellular magnetic dipole moment beyond the value needed to overcome Brownian motion in geomagnetic field conditions.     

Carbon nanotube clusters as universal bacterial adsorbents and magnetic separation agents

The magnetic susceptibility and high bacterial affinity of carbon nanotube (CNT) clusters highlight their great potential as a magnetic bio‐separation agent. This article reports the CNT clusters' capability as “universal” bacterial adsorbents and magnetic separation agents by designing and testing a multiwalled carbon nanotube (MWNT) cluster‐based process for bacterial capturing and separation. The reaction system consisted of large clusters of MWNTs for bacterial capture and an external magnet for bio‐separation. The designed system was tested and optimized using Escherichia coli as a model bacterium, and further generalized by testing the process with other representative strains of both gram‐positive and gram‐negative bacteria. For all strains tested, bacterial adsorption to MWNT clusters occurred spontaneously, and the estimated MWNT clusters' adsorption capacities were nearly the same regardless of the types of strains. The bacteria‐bound MWNT clusters also responded almost instantaneously to the magnetic field by a rare‐earth magnet (0.68 Tesla), and completely separated from the bulk aqueous phase and retained in the system. The results clearly demonstrate their excellent potential as highly effective “universal” bacterial adsorbents for the spontaneous adsorption of any types of bacteria to the clusters and as paramagnetic complexes for the rapid and highly effective magnetic separations. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Multiplexed detection of foodborne pathogens based on magnetic particles

This paper addresses the novel approaches for the multiplex detection of food poisoning bacteria, paying closer attention to three of the most common pathogens involved in food outbreaks: Salmonella enterica, Escherichia coli O157:H7 and Listeria monocytogenes. End-point and real-time PCR, classical immunological techniques, biosensors, microarrays and microfluidic platforms, as well as commercial kits for multiplex detection of food pathogens will be reviewed, with special focus on the role of magnetic particles in these approaches. Although the immunomagnetic separation for capturing single bacteria from contaminating microflora and interfering food components has demonstrated to improve the performance on these approaches, the integration of magnetic particles for multiplex detection of bacteria is still in a preliminary stage and requires further studies.     

Steroid transformation using magnetically immobilized Mycobacterium sp.

Mycobacterium sp. (NRRL-B 3683) has been immobilized by adhesion of magnetic materials of submicron size to the bacterial surface. Preparations based on laboratory-prepared magnetic oxide that had been derivatized with hydrophobic octyltrichlorosilane showed the best properties. The magnetically immobilized bacteria were used for side-chain degradation of cholesterol into androsta-1,4-diene-3,17-dione. The magnetic bacteria behaved as free cells in the transformation media and no mass transfer limitations were observed. The magnetic bacteria could be used repeatedly without any cell loss, the cells being retrieved at the end of each transformation cycle by a magnet.     

Birefringence determination of magnetic moments of magnetotactic bacteria

A birefringence technique is used to determine the average magnetic moments <μ> of magnetotactic bacteria in culture. Differences in <μ> are noted between live and dead bacteria, as well as between normal density and high density samples of live bacteria.     

The Influence of Low Magnetic Fields and Magnesium Isotopes on <Emphasis Type="Italic">E. coli</Emphasis> Bacteria

The combined effects of external low static magnetic fields at 0–22 mT and magnesium isotopes on the growth and development of E. coli bacteria has been studied. The magnetic field and ²⁵Mg magnetic isotope effects were obtained in two ranges: 0.8–3.0 and 8–13 mT. The experimental values of the growth rate, the number of CFUs and the ATP pool of bacteria enriched in magnetic magnesium isotope ²⁵Mg (nuclear spin, I = 5/2) in the range of 0.8–3.0 mT are significantly higher compared to bacteria enriched in nonmagnetic isotopes ²⁴Mg, ²⁶Mg, or natural magnesium. The increase in the growth rate, colony-forming ability, and intracellular ATP concentration in bacteria in all groups cultivated under exposure to an external static magnetic field in the range of 0.8 to 3.0 mT confirms the existence of magnetosensitive stages of enzymatic reactions that proceed via the ion-radical mechanism. The combined influence of the magnetic field in the range of 8 to 13 mT and the magnesium magnetic isotope ²⁵Mg on the colony forming ability of E. coli bacteria is associated with processes that are responsible for cell division. The above-mentioned effects of bacterial magnetosensitivity (to magnetic fields and magnetic isotopes) are in good agreement with theoretical predictions of the theory of spin-dependent enzymatic reactions.     

Pathogen detection by core–shell type aptamer-magnetic preconcentration coupled to real-time PCR

The presence of pathogenic bacteria is a major health risk factor in food samples and the commercial food supply chain is susceptible to bacterial contamination. Thus, rapid and sensitive identification methods are in demand for the food industry. Quantitative polymerase chain reaction (PCR) is one of the reliable specific methods with reasonably fast assay times. However, many constituents in food samples interfere with PCR, resulting in false results and thus hindering the usability of the method. Therefore, we aimed to develop an aptamer-based magnetic separation system as a sample preparation method for subsequent identification and quantification of the contaminant bacteria by real-time PCR. To achieve this goal, magnetic beads were prepared via suspension polymerization and grafted with glycidylmethacrylate (GMA) brushes that were modified into high quantities of amino groups. The magnetic beads were decorated with two different aptamer sequences binding specifically to Escherichia coli or Salmonella typhimurium. The results showed that even 1.0% milk inhibited PCR, but our magnetic affinity system capture of bacteria from 100% milk samples allowed accurate determination of bacterial contamination at less than 2.0 h with limit of detection around 100 CFU/mL for both bacteria in spiked-milk samples.