Showing papers on "Magnetotactic bacteria published in 1995"
TL;DR: The results show that in some magnetotactic bacteria, external environmental conditions such as redox and/or oxygen or hydrogen sulfide concentrations may affect the composition of the nonmetal part of the magnetosome mineral phase.
Abstract: A slowly moving, rod-shaped magnetotactic bacterium was found in relatively large numbers at and below the oxic-anoxic transition zone of a semianaerobic estuarine basin. Unlike all magnetotactic bacteria described to date, cells of this organism produce single-magnetic-domain particles of an iron oxide, magnetite (Fe(inf3)O(inf4)), and an iron sulfide, greigite (Fe(inf3)S(inf4)), within their magnetosomes. The crystals had different morphologies, being arrowhead or tooth shaped for the magnetite particles and roughly rectangular for the greigite particles, and were coorganized within the same chain(s) in the same cell with their long axes along the chain direction. Because the two crystal types have different crystallochemical characteristics, the findings presented here suggest that the formation of the crystal types is controlled by separate biomineralization processes and that the assembly of the magnetosome chain is controlled by a third ultrastructural process. In addition, our results show that in some magnetotactic bacteria, external environmental conditions such as redox and/or oxygen or hydrogen sulfide concentrations may affect the composition of the nonmetal part of the magnetosome mineral phase.
251 citations
TL;DR: In this article, a simple optical method was developed for assaying cellular magnetism in culture samples of magnetic spirilla, where cells are aligned parallel to the field lines in a magnetic field, resulting in a change in light scattering.
Abstract: A simple optical method was developed for assaying cellular magnetism in culture samples of magnetic spirilla. Cells are aligned parallel to the field lines in a magnetic field, resulting in a change in light scattering. The ratio of scattering intensities at different angles of magnetic field relative to the light beam (Cmag) is used to characterize the average magnetic orientation of the cells. Cmag was found to be well correlated with the average number of particles in different magnetic cell populations. Thus, estimations of magnetosome content can be made using magnetically induced differential light scattering. The method provides a fast and sensitive tool for monitoring the magnetite formation in growing cultures of Magnetospirillum gryphiswaldense.
146 citations
138 citations
TL;DR: In this paper, a magnetic force microscope (MFM) was used to image topography and magnetic forces from a chain of submicron single magnetic domain particles produced by and contained in isolated magnetotactic bacteria.
Abstract: A magnetic force microscope (MFM) was used to image topography and magnetic forces from a chain of submicron single magnetic domain particles produced by and contained in isolated magnetotactic bacteria. The noncontact magnetic force microscope data were used to determine a value for the magnetic moment of an individual bacterial cell, of order 10−13 emu, consistent with the average magnetic moment of bacteria from the same sample, obtained by superconducting quantum interference device magnetometry. The results represent the most sensitive quantification of a magnetic force microscope image to date.
135 citations
TL;DR: H hippocampal material from deceased normal and epileptic subjects, and from the surgically removed epileptogenic zone of a living patient, had magnetic characteristics similar to those reported for other parts of the brain, which indicate that the magnetic material is present in a wide range of grain sizes.
95 citations
TL;DR: In this paper, the authors describe pulsed-magnetic field remanence measurements of individual, killed, undisrupted cells of three different types of magnetotactic bacteria, and show that for MM cells, the hysteresis loop is square, with the coercive field variable from cell to cell.
82 citations
TL;DR: The phylogenetic diversity of magnetic cocci was found to exceed the variety of distinguishable morphotypes and sequence differences between 16S rDNAs of closely related magnetotactic cocci were indeed present in the 15S rRNA and not due to sequencing or PCR artifacts.
68 citations
TL;DR: RS-1 is the first bacterium reported outside the alpha-Proteobacteria that contains magnetite inclusions, and it appears to represent a new genus, suggesting that intracellular magnetite biomineralization is of multiple evolutionary origins.
Abstract: Most of the 16S ribosomal RNA gene of a sulfate-reducing magnetic bacterium, RS-1, was sequenced, and phylogenetic analysis was carried out. The results suggest that RS-1 is a member of the δ-Proteobacteria, and it appears to represent a new genus. RS-1 is the first bacterium reported outside the α-Proteobacteria that contains magnetite inclusions. RS-1 therefore disrupts the correlation between the α-Proteobacteria and possession of magnetite inclusions, and that between the δ-Proteobacteria and possession of greigite inclusions. The existence of RS-1 also suggests that intracellular magnetite biomineralization is of multiple evolutionary origins.
61 citations
TL;DR: The model describes the motion of a non-magnetotactic coccus bacterium swimming in a fluid and suggests that the strong helical pattern observed in typical trajectories of magnetotactic bacteria can be a biological advantage complementary to magnetic orientation.
Abstract: Motion of flagellate bacteria is considered from the point of view of rigid body mechanics. As a general case we consider a flagellate coccus magnetotactic bacterium swimming in a fluid in the presence of an external magnetic field. The proposed model generalizes previous approaches to the problem and allows one to access parameters of the motion that can be measured experimentally. The results suggest that the strong helical pattern observed in typical trajectories of magnetotactic bacteria can be a biological advantage complementary to magnetic orientation. In the particular case of zero magnetic interaction the model describes the motion of a non-magnetotactic coccus bacterium swimming in a fluid. Theoretical calculations based on experimental results are compared with the experimental track obtained by dark field optical microscopy.
39 citations
TL;DR: Magnetotactic bacteria (MB)-cocci as well as a spirillum of type Magnetospirillum gryphiswaldense-were investigated for their applicability for nondestructive domain analysis on soft magnetic materials as discussed by the authors.
Abstract: Magnetotactic bacteria (MB)-cocci as well as a spirillum of type Magnetospirillum gryphiswaldense-were investigated for their applicability for nondestructive domain analysis on soft magnetic materials. Solely magnetotactic cocci which show a definite swimming direction proved to be suitable for this purpose. The intensity of the domains' magnetic stray field H of coated SiFe sheets proved to be high enough to visualize main domains even in distances of 500 /spl mu/m from the specimen surface, in comparison to about 5 /spl mu/m for colloid particles. Thus it was possible to develop a specific "domain viewer" which allows simple handling and reuse of bacteria for repeated analysis. Based on theoretical considerations about the cocci's motion in a magnetic field, a computer program for the simulation of spatiotemporal bacterial distributions was developed. Results show that-in contrast to colloid techniques and nonmotile bacteria-the gradient of H does not influence the contrast in an essential way. Due to Brownian motion of motile bacteria, a minimum domain width is required for effective visualizations. This was confirmed by experimental results of both secondary domains of crystalline specimens and narrow surface domains of amorphous bands. However, for small domain structures of the latter, unmotile dead bacteria proved to be applicable. Finally, influences of bacterial concentrations on the contrast as well as the contrast mechanism as a function of time are discussed. >
27 citations
TL;DR: An accurate quantification of magnetic force microscope images has been accomplished as discussed by the authors, using magnetosomes produced by magnetotactic bacteria, an ideal micromagnetic model system, were the specimens used for the quantification (a moment on the order of 10 −13 emu).
01 Jan 1995
TL;DR: This chapter describes the isolation and cultivation of magnetotactic bacteria, the separation and characterization of magnetic ultrafine particles ( UFPs), the immobilization of enzymes and antibodies on the particles, and their incorporation into animal cells.
Abstract: Publisher Summary This chapter describes the isolation and cultivation of magnetotactic bacteria, the separation and characterization of magnetic ultrafine particles ( UFPs), the immobilization of enzymes and antibodies on the particles, and their incorporation into animal cells. The isolation and cultivation of the fresh water helical magnetotactic bacterium, Aquaspirillum magetotacticum, strain MS-l was reported. Separation of the magnetotactic bacteria was carried out in a semisolid culture containing about 10% filtered sterilized swamp water, organic acids, vitamin, inorganic salts, and agar. The magnetotactic bacteria were mass cultivated in mud. The optimal conditions for cultivating magnetotactic bacteria were obtained through a series of experiments in which the conditions were systematically varied. The effects of carbon and nitrogen sources were evaluated to increase the growth rate of the bacteria. There are a number of reports on the characterization and separation of bacterial magnetic particles. The magnetic fine particles collected from magnetotactic bacteria cultivated in mud were characterized. The collected bacteria were further concentrated and separated using a centrifuge. Various antibodies were immobilized on bacterial magnetic particles and artificial magnetic UFPs, and measurements of the bacterial count and carcino embryonic antigens (CEA) were done. CEA detection was done using CEA antibodies immobilized on bacterial magnetic particles. Ordinary animal cells and microorganisms do not contain magnetic particles. However, if magnetic particles can be introduced into these cells, it would be possible to magnetically move the cells, which would make it possible to treat the cells in a variety of ways.