Showing papers on "Magnetotactic bacteria published in 1993"
TL;DR: A combination of polymerase chain reaction-assisted rRNA sequence retrieval and fluorescent oligonucleotide probing was used to identify in situ a hitherto unculturable, big, magnetotactic, rod-shaped organism in freshwater sediment samples collected from Lake Chiemsee.
Abstract: A combination of polymerase chain reaction-assisted rRNA sequence retrieval and fluorescent oligonucleotide probing was used to identify in situ a hitherto unculturable, big, magnetotactic, rod-shaped organism in freshwater sediment samples collected from Lake Chiemsee. Tentatively named "Magnetobacterium bavaricum," this bacterium is evolutionarily distant from all other phylogenetically characterized magnetotactic bacteria and contains unusually high numbers of magnetosomes (up to 1,000 magnetosomes per cell). The spatial distribution in the sediment was studied, and up to 7 x 10 active cells per cm were found in the microaerobic zone. Considering its average volume (25.8 +/- 4.1 mum) and relative abundance (0.64 +/- 0.17%), "M. bavaricum" may account for approximately 30% of the microbial biovolume and may therefore be a dominant fraction of the microbial community in this layer. Its microhabitat and its high content of sulfur globules and magnetosomes suggest that this organism has an iron-dependent way of energy conservation which depends on balanced gradients of oxygen and sulfide.
251 citations
TL;DR: Phylogenetic analyses of small subunit ribosomal RNA sequences showed that all known magnetotactic bacteria of the iron oxide type are associated with the a subgroup of the Proteobacteria in the domain Bacteria, and suggest that magnetotaxis based on iron oxides and iron sulfides evolved independently.
Abstract: Magnetosomes are intracellular, iron-rich, membrane-enclosed magnetic particles that allow magnetotactic bacteria to orient in the earth's geomagnetic field as they swim. The magnetosomes of most magnetotactic bacteria contain iron oxide particles, but some magnetotactic species contain iron sulfide particles instead. Phylogenetic analyses of small subunit ribosomal RNA sequences showed that all known magnetotactic bacteria of the iron oxide type are associated with the a subgroup of the Proteobacteria in the domain Bacteria. In contrast, uncultured magnetotactic bacteria of the iron sulfide type are specifically related to the dissimilatory sulfate-reducing bacteria within the delta subdivision of the Proteobacteria. These findings indicate a polyphyletic origin for magnetotactic bacteria and suggest that magnetotaxis based on iron oxides and iron sulfides evolved independently.
241 citations
TL;DR: Intracellular magnetite (Fe3O4) crystals produced by the magnetotactic bacterium MC-1 were analysed by transmission electron microscopy (TEM) and showed that the crystal morphology was controlled even at early stages of development.
Abstract: Magnetite (Fe$\_{3}$O$\_{4}$) crystals produced by two strains of cultured vibrioid magnetotactic bacteria were studied by high-resolution transmission electron microscopy (HRTEM). Both magnetotactic strains were characterized by single chains of magnetite crystals aligned along the long axes of the cells. The strains, designated as MV-2 and MV-4, produced crystals that differed markedly in size and morphology. Crystals present in MV-4 cells were generally larger than those in MV-2 cells and displayed significantly smaller aspect ratios. Crystallographic analysis of the magnetosomes of MV-2 revealed an elongated hexagonal habit based on a prism of {110} faces capped by {111} faces. The axis of elongation was parallel to the direction. This morphology closely resembles the crystal shape of magnetosomes in a previously described vibrioid species MV-1. In contrast, magnetosomes of MV-4 possessed a cubo-octahedral morphology which was modified by a small elongation along the direction. Although this morphology has not previously been observed in magnetotactic bacteria, it appears to be intermediate between the regular cubo-octahedral shape of magnetosomes in the cultured species Aquaspirillum magnetotacticum and the extensively elongated cubo-octahedral crystals of a previously studied uncultured ovoid-shaped magnetotactic bacterium. The results support the proposal that the crystal morphologies of bacterial magnetite are strain specific.
180 citations
TL;DR: In this paper, the first systematic findings of magnetotactic bacteria in pelagic and hemipelagic sediments of the eastern South Atlantic were reported, and different morphologies were identified (cocci, spirilla, vibrionic and rod-shaped forms) at water depths to about 3000 m on the African continental margin between the equator and 30°S, and on the Walvis Ridge in a pelagic environment about 1400 km off the coast.
117 citations
13 Apr 1993
TL;DR: In this article, the response of magnetotactic bacteria to an applied magnetic field has been analyzed using image processing techniques, including magnetic movement, and magnetic properties of the bacteria with a higher rate and with greater accuracy.
Abstract: The response of magnetotactic bacteria to an applied magnetic field has been analyzed using image processing techniques. Bacterial characteristics, including magnetic movement, have been processed at a higher rate and evaluated with greater accuracy. This method offers a unique tool in data analysis and enhancement for recorded images of biological systems. >
27 citations
TL;DR: In this article, a pure culture of magnetospirillum gryphiswaldense as well as a natural population of cocci were investigated, which showed a linear relation of the measured susceptibility χ with the concentration of magnetotactic bacteria.
Abstract: High concentrations of magnetotactic bacteria are needed for their practical applications, as investigations of domains in soft magnetic materials. The present paper reports experimental studies, the initial aim of which has been to determine the concentration c of magnetotactic bacteria within a culture medium from the measured susceptibility χ. A pure culture of Magnetospirillum gryphiswaldense as well as a natural population of cocci were investigated. M. gryphiswaldense showed a linear relation of the measured χ with the concentration c. Cocci showed characteristics which complicate the determination of c. Problems of manipulation of cocci by means of magnetic fields are discussed. For an effective interpretation of χ attempts were made to divide natural populations in sub-populations of more uniform characteristics by a magnetophoresis technique and by changing the polarity of bacteria.
20 citations
TL;DR: In this article, the authors describe the characterization of a magnetotactic spirillum and the implications these results have for its use in the clean up of environmental pollution, and propose a new mechanism for the biomineralization of magnetite.
Abstract: Magnetotactic bacteria possess a magnetic moment due the presence of membrane bounded crystals of magnetite, (Fe3O4) called magnetosomes within their structure. Through manipulation in an applied magnetic field it is possible to determine the size, speed, and magnetic moment of individual bacteria, and hence an average for a culture. Variations in these characteristics with growth have been measured, indicating the suitability of this particular magnetic spirillum for metal loading. A correlation between the increase in magnetic moment and iron uptake of this bacterium leads us to propose a new mechanism for the biomineralization of magnetite. This paper describes the characterization of a magnetotactic spirillum and the implications these results have for its use in the clean up of environmental pollution.
17 citations
01 Jan 1993
TL;DR: The study of fine-particle magnetism is of importance because of the natural abundance of various fineparticle materials, and because the special properties of finely divided materials lead to their utilization in a wide range of manufactured goods as mentioned in this paper.
Abstract: The study of fine-particle magnetism is of importance because of the natural abundance of various fine-particle materials, and because the special properties of finely divided materials lead to their utilization in a wide range of manufactured goods. Naturally occurring fine particles include the chains of magnetite particles found in magnetotactic bacteria, the several grams of iron stored in the human body as the ferrihydrite cores of storage proteins, and the magnetic phases and weathering products found in rocks, soils, and coals. Manufactured magnetic fine particles include the magnetite particles used in fluid seals and bearings, and the particles of maghemite, barium ferrite, and others used in computer hard and floppy disks, credit cards, and audio and video recording tapes.
12 citations
TL;DR: In this paper, the authors used magnetotactic bacteria that swim along the lines of the magnetic field originating from the poles on the tip of a magnetic head to observe the magnetic structure of the tip.
Abstract: MFM images of a magnetic head and a recording medium obtained by using electrodeposited FeNi, Co, and FeCo tips show quite different features. These differences are explained by the saturation magnetization and the coercive force of the magnetic thin films electrodeposited on the W wires, In addition, we attempted to observe the magnetic structure of the tip by using magnetotactic bacteria that swim along the lines of the magnetic field originating from the poles on the tip.
2 citations