Showing papers on "Magnetotactic bacteria published in 1996"
TL;DR: In this paper, a mechanism for the formation of secondary ferrimagnetic minerals that links abiological weathering and biological fermentation processes was proposed, which may be linked to climate, and observed causative associations between climate and the magnetic susceptibility of loess-palaeosol sequences are supported by the findings.
Abstract: Magnetic susceptibility values for topsoils across England arc combined with data for soil type, geochemistry and concentrations of magnetotactic bacteria in order to evaluate different theories for explaining soil magnetism. Strongly magnetic soils in unpolluted areas are found over weakly magnetic substrates and are dominated by ultrafine superparamagnetic grains. Magnetotactic bacteria are present in insufficient concentrations to account for strongly magnetic soils, and crop burning is discounted as a major factor. A small number of samples show high values associated with either airborne magnetic particulates from pollution or residual primary ferrimagnetic minerals from igneous substrates. The results are used to construct a new mechanism for the formation of secondary ferrimagnetic minerals that links abiological weathering and biological fermentation processes. The fundamental driving force in the mechanism is Fe supply, which may be linked to climate. Observed causative associations between climate and the magnetic susceptibility of loess-palaeosol sequences are supported by the findings.
388 citations
TL;DR: However, there is some accumulating evidence that suggests that in certain organisms under specific situations, local environmental conditions appear to affect the magnetosome mineral phase in at least three different ways.
73 citations
TL;DR: In this paper, the spatial arrangement of magnetosomes in cells of two morphologically different types of magnetotactic bacteria which possess at least two chains was investigated using scanning and transmission electron microscopy (SEM/TEM).
62 citations
TL;DR: A multidisciplinary approach involving rock-magnetics, transmission electron microscopy, and X-ray diffraction was used to identify a biogenic magnetite component in the Lake Baikal, Siberia, sedimentary magnetic record.
35 citations
TL;DR: In this paper, a new approach to the determination of the magnetic moment of non-spherical magnetotactic bacteria is described by studying the reaction of nonmotile bacteria to applied homogenous magnetic fields.
Abstract: A new approach to the determination of the magnetic moment of non-spherical magnetotactic bacteria is described. This is achieved by studying the reaction of non-motile bacteria to applied homogenous magnetic fields. The magnetic moment is calculated from the 'flip time' of a magnetotactic bacterium as its dipole realigns itself when the polarity of the applied magnetic field is reversed. The results are compared with measurements obtained from three other techniques.
30 citations
TL;DR: The successful isolation of RS-1 by this method suggests the presence of magnetic bacteria which exist in a non-magnetic state in sediments, and allows isolation of non-motile and non- or weakly-magnetotactic bacteria, which would not accumulate in the absence of an applied magnetic field.
26 citations
TL;DR: In this paper, a comparison of high gradient magnetic separation (HGMS) and low field orientational magnetic separation is made and conditions under which HGMS becomes beneficial are considered.
Abstract: Motile magnetotactic bacteria are normally separated from a solution by applying a low intensity (mT) orientating magnetic field. This constrains the bacteria to swim in the required direction. High gradient magnetic separation (HGMS) is a well established method for the extraction of magnetic particles from solutions. This paper reports on the separation properties of both motile and non-motile magnetotactic bacteria using both techniques. A comparison of HGMS separation with low field orientational magnetic separation is made and the conditions under which HGMS becomes beneficial are considered.
16 citations
01 Jan 1996
12 citations
Journal Article•
4 citations
TL;DR: The first detection of magnetic material in the human brain through the use of SQUID magnetometry is reported and it is shown that the distribution of magnetite is rather even in the whole human brain averaging 4 ng per gram of tissue.
Abstract: Ferritin, the iron storage nonhaeme-protein contains a ball of hydrated iron oxides (Fe2O3⋅nH2O) in its core, which is paramagnetic at room temperature. It is reported the hydrated iron oxide is the precursor of magnetite (Fe3O4) in the magnetotactic bacteria and polyplacophoran mollusks. It is not known whether this is the case for other organisms. In our study, we report the first detection of magnetic material in the human brain through the use of SQUID magnetometry. The material was characterized by HRTEM and EPMA. It was affirmed the material was a single crystals of magnetite. Magnetite distribution in tissues might be related with ferritin, if the core of these molecules are involved in magnetite formation in human. In general, both Perls staining and MRlmaging methods are adopted routinely for determining the relative amounts of Fe(+III) in the whole brain, which is dominated by ferritin. Both methods suggested high levels of Fe(+III) distribution in the globus pallidum, putamen, caudate, internal cerebral capsule of the cerebrum, red nucleus of the mid brain and lower concentrations in the substantia nigra of the mid brain and the dentate nucleus of the cerebellum. Whereas, our experiments showed that the distribution of magnetite is rather even in the whole human brain averaging 4 ng per gram of tissue (except for the meninges, where it is 20 times higher).
TL;DR: In this paper, a pairwise, far-field, hydrodynamic interactions between swimming bacteria are proposed to be responsible for the band structure that appears when such bacteria are oriented in a given direction by an external magnetic field.
Abstract: This paper reports the results of simulations of the motion of dense suspensions of magnetotactic bacteria, bacteria that contain small magnetic dipoles. These simulations build on a previously described mechanism in which pair-wise, far-field, hydrodynamic interactions between swimming bacteria are proposed to be responsible for the band structure that appears when such bacteria are oriented in a given direction by an external magnetic field. Previous work has shown that these hydrodynamic forces act in a direction and with a magnitude that are fully consistent with the observed behavior. Applying this pair-wise, hydrodynamic force mechanism to hundreds of bacteria in a numerical simulation shows that band formation and stability is predicted by this simple model, while the precise band shape appears to depend on effects not included in the simulation.