Showing papers on "Magnetotactic bacteria published in 2001"
TL;DR: A major gene cluster containing several magnetosome genes (including mamA and mamB) was found to be conserved in all three of the strains investigated and contains additional genes that have no known homologs in any nonmagnetic organism, suggesting a specific role in magnetosomes formation.
Abstract: In magnetotactic bacteria, a number of specific proteins are associated with the magnetosome membrane (MM) and may have a crucial role in magnetite biomineralization. We have cloned and sequenced the genes of several of these polypeptides in the magnetotactic bacterium Magnetospirillum gryphiswaldense that could be assigned to two different genomic regions. Except for mamA, none of these genes have been previously reported to be related to magnetosome formation. Homologous genes were found in the genome sequences of M. magnetotacticum and magnetic coccus strain MC-1. The MM proteins identified display homology to tetratricopeptide repeat proteins (MamA), cation diffusion facilitators (MamB), and HtrA-like serine proteases (MamE) or bear no similarity to known proteins (MamC and MamD). A major gene cluster containing several magnetosome genes (including mamA and mamB) was found to be conserved in all three of the strains investigated. The mamAB cluster also contains additional genes that have no known homologs in any nonmagnetic organism, suggesting a specific role in magnetosome formation.
274 citations
TL;DR: It is suggested that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process and are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.
Abstract: McKay et al. [(1996) Science 273, 924-930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe(3)O(4)) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found.
156 citations
TL;DR: Although it is unlikely that magnetotactic bacteria were ever alive in ALH84001, decomposed remains of such organisms could have been deposited in cracks in the rock while it was still on the surface on Mars.
Abstract: The presence of magnetite crystal chains, considered missing evidence for the biological origin of magnetite in ALH84001 [Thomas-Keprta, K. L., Bazylinski, D. A., Kirschvink, J. L., Clemett, S. J., McKay, D. S., Wentworth, S. J., Vali, H., Gibson, E. K., Jr., & Romanek, C. S. (2000) Geochim. Cosmochim. Acta 64, 4049-4081], is demonstrated by high-power stereo backscattered scanning electron microscopy. Five characteristics of such chains (uniform crystal size and shape within chains, gaps between crystals, orientation of elongated crystals along the chain axis, flexibility of chains, and a halo that is a possible remnant of a membrane around chains), observed or inferred to be present in magnetotactic bacteria but incompatible with a nonbiological origin, are shown to be present. Although it is unlikely that magnetotactic bacteria were ever alive in ALH84001, decomposed remains of such organisms could have been deposited in cracks in the rock while it was still on the surface on Mars.
98 citations
TL;DR: In this article, the magnetic microstructure of magnetotactic bacteria is characterized using off-axis electron holography in the transmission electron microscope using single cells of strains MV-1 and MS-1.
Abstract: Off-axis electron holography in the transmission electron microscope is used to characterize the magnetic microstructure of magnetotactic bacteria. The practical details of the technique are illustrated through the examination of single cells of strains MV-1 and MS-1, which contain crystals of magnetite (Fe 3 O 4 ) that are ∼50 nm in size and are arranged in chains. Electron holography allows the magnetic domain structures within the nanocrystals to be visualized directly at close to the nanometer scale. The crystals are shown to be single magnetic domains. The magnetization directions of small crystals that would be superparamagnetic if they were isolated are found to be constrained by magnetic interactions with adjacent, larger crystals in the chains. Magnetization reversal processes are followed in situ , allowing a coercive field of between 30 and 45 mT to be measured for the MV-1 cell. To within experimental error, the remanent magnetizations of the chains are found to be equal to the saturation magnetization of magnetite (0.60T). A new approach is used to determine that the magnetic moments of the chains are 7 and 5×10 −16 Am 2 for the 1600-nm long MV-1 and 1200-nm long MS-1 chains examined, respectively. The degree to which the observed magnetic domain structure is reproducible between successive measurements is also addressed.
84 citations
TL;DR: A brackish lagoon at Itaipu, Brazil, contains magnetotactic bacteria with unusually large magnetite magnetosomes (lengths 100-200 nm).
Abstract: A brackish lagoon at Itaipu, Brazil, contains magnetotactic bacteria with unusually large magnetite magnetosomes (lengths 100–200 nm). The micromagnetic structures of the magnetosomes from two different coccoid organisms from the lagoon have been determined by electron holography. The results are consistent with single-magnetic-domain structure in the elongated magnetosomes from one organism and metastable, single-magnetic-domain structure in the larger, more equi-axed, magnetosomes from the other organism. The results are consistent with theoretical predictions of the transition dimension between stable and metastable single-domain structure in magnetite.
57 citations
TL;DR: In this article, a range of mineral magnetic, Mossbauer, geochemical, microscopy and molecular biological techniques are applied to a small set of bulk and fine fractions of highly magnetic English topsoils that overlie weakly magnetic sedimentary geologies.
Abstract: SUMMARY A range of mineral magnetic, Mossbauer, geochemical, microscopy and molecular biological techniques are applied to a small set of bulk and fine fractions of highly magnetic English topsoils that overlie weakly magnetic sedimentary geologies. Results show that the ferrimagnetic component of highly enhanced surface soils is dominated by superparamagnetic (SP) grains with a minor proportion of larger stable single- domain/pseudo-single-domain (SSD/PSD) grains that may derive from magnetosomes and magnetic inclusions. DNA screening of the soils by polymerase chain reaction (PCR) shows that the concentration of viable magnetotactic bacteria is too low (normally <10 2 bacteria g x1 ) to explain the high concentrations of ferrimagnetic minerals observed. There does not appear to be any strong causative relationship between the presence or concentration of Magnetospirillum sp. and soil magnetic properties. Microcosm experiments were able to show that the destructive effects of waterlogging on secondary ferrimagnetic mineral (SFM) formation are rapid and associated with significant changes in bacterial populations. The combined results are used to examine alternative explanations for SFM formation and are consistent with previous findings (Dearing et al. 1996b, 1997) that ferrihydrite may be an important precursor of bacterially mediated magnetite in strongly magnetic temperate soils—a process driven by the rate of Fe flux to the biologically active surface soil.
52 citations
TL;DR: In this paper, the discovery of nanocrystalline botanical magnetite in iron-rich extracts from disrupted grass cells was reported, with the smallest cubo-octahedral botanical nanocrystals (4 ± 1 nm) are an order of magnitude smaller than their bacterial counterparts.
Abstract: Based on transmission electron microscopy and electron diffraction observations, we report the discovery of nanocrystalline botanical magnetite in iron-rich extracts from disrupted grass cells. The majority of the magnetite nanocrystals extracted from the grass plants display cubo-octahedral shapes, with a minority of hexagonal prism morphologies. In addition to the constrained morphologies, each group has a narrow size distribution typical of intracellular-boundary organized biomineralization processes responsible for bacterial magnetite. The smallest cubo-octahedral botanical nanocrystals (4 ± 1 nm) are an order of magnitude smaller than their bacterial counterparts. These botanical nanocrystals are self-organized in ordered, micrometer-sized agglomerates, distinct from magnetite strings in magnetotactic bacteria and similar to some pedogenic magnetite currently attributed to inorganic processes. We discuss the implications of our findings on the search for magnetite records of extraterrestrial and ancient terrestrial life, the origin of the terrestrial topsoil magnetite, and the potential for bioremediation using botanical magnetite.
52 citations
TL;DR: Observations demonstrate that the structures of the magnetite particles in ALH84001, their spatial arrangement and coprecipitation with carbonates and proximity to silicates are consistent with being biogenic.
Abstract: We report biogenic magnetite whiskers, with axial ratios of 6: 1, elongated in the [1 1 1]. [1 1 2] and [1 0 0] directions, resembling the magnetite whiskers detected in the Martian meteorite ALH84001 by Bradley ct nl., and interpreted by those authors as evidence of vapour-phase (abiogenic) growth. Magnetosomal whiskers with extended defects consistent with screw dislocations and magnetosomes resembling flattened twinned platelets, as well as other twinning phenomena and other structural defects, are also reported here. Magnetosomes with teardrop-shaped. cuboidal. irregular and jagged structures similar to those detected in ALH84001 by McKay et al.. coprecipitation of magnetite possibly with amorphous calcium carbonate, coprecipitation of magnetite possibly with amorphous silica, the incorporation of titanium in volutin inclusions and disoriented arrays of magnetosomes are also described. These observations demonstrate that the structures of the magnetite particles in ALH84001. their spatial arrange ment and coprecipitation with carbonates and proximity to silicates are consistent with being biogenic. Electron-beam-induced flash-melting of magnetosomes produced numerous screw dislocations in the (1 1 1). (1 0 0) and (1 1 0) lattice planes and induced fusion of platelets. From this, the lack of screw dislocations reported in the magnetite particles in ALH84001 (McKay et al.. and Bradley et al.) indicates that they have a low-temperature origin.
46 citations
TL;DR: The phosphorus-rich granules are major sites for metal accumulation by these bacteria, and no conclusive results for magnetosomes were obtained because of the limitations of the analytical techniques particularly when used for whole cell analysis.
Abstract: Natural enrichments of magnetotactic bacteria were used to study the sites where heavy metals accumulate in uncultured bacteria. Most bacteria obtained by magnetic concentration from these enrichments contained, in addition to the magnetosomes, large phosphorus-rich granules in the cytoplasm. Metal (Zn, Mn, Sr, Cd, Al, Cr, and Pb) chlorides were added independently to the enrichments, and after 24 h, the elemental composition of the phosphorus-rich granules, magnetosomes, and "soft parts" (cytoplasm plus cell envelope) of whole bacteria was analyzed by energy-dispersive X-ray analysis on a transmission electron microscope. All bacteria contained Mn and Sr in the phosphorus-rich granules; some of them presented Mn peaks also in the soft parts. Zinc accumulation was variable and was found mainly in the phosphorus-rich granules, but also in the soft part of some bacteria. Some analyzed bacteria presented Zn peaks only in the soft parts, and some of them did not present Zn in any structure. Cadmium and Al were found only in the granules of some bacteria. Chromium was found in the soft parts of some bacteria. Lead was not detected in any bacteria. We concluded that the phosphorus-rich granules are major sites for metal accumulation by these bacteria. No conclusive results for magnetosomes were obtained because of the limitations of the analytical techniques particularly when used for whole cell analysis.
18 citations
TL;DR: In this paper, the synthesis of nano-sized magnetite particles was carried out following a polymer matrix mediated process and the produced particles were oriented perpendicularly with respect to polymeric tubules and showed a tendency of array formation.
Abstract: Synthesis of nano sized magnetite particles has been carried out following a polymer matrix mediated process. The synthesis route, being akin to bio mineralization, yields elongated magnetite particles of uniform size and morphology. The produced particles were oriented perpendicularly with respect to polymeric tubules and showed a tendency of array formation as happens in magnetotactic bacteria.
15 citations
TL;DR: It is shown that reflections from bacterial cells are uniquely associated with the magnetite, which underpins the magnetotactic response of the bacteria.
19 Apr 2001
TL;DR: This article describes the occurrence, structure, arrangement and function of bacterial intracytoplasmic membranes (ICMS) including magnetosomes of magnetotactic bacteria, the thylakoids of cyanobacteria and chloroxybacteria, the ICMS of purple bacteria and chemoautotrophic bacteria and the chlorosome of green bacteria.
Abstract: This article describes the occurrence, structure, arrangement and function of bacterial intracytoplasmic membranes (ICMS) including magnetosomes of magnetotactic bacteria, the thylakoids of cyanobacteria and chloroxybacteria, the ICMS of purple bacteria and chemoautotrophic bacteria and the chlorosomes of green bacteria.
Keywords:
thylakoids;
phycobilisomes;
intracytoplasmic membrane (ICM);
chlorosome
TL;DR: In this article, an electronic control system for the measurement of hysteresis curves of microscopically observed magnetic structures such as chains of magnetosomes in magnetotactic bacteria suspended or swimming in water is described.
Abstract: An electronic control system for the measurement of hysteresis curves of microscopically observed magnetic structures such as chains of magnetosomes in magnetotactic bacteria suspended or swimming in water is described. Using continuous magnetic fields generated by four coils for guidance or orientation of the bacteria or other magnetic structures, and pulsed magnetic fields in two additional coils for changing the degree of magnetization in small steps, hysteresis curves can be traversed. The circuits described can be constructed with readily available components. The guiding- and pulsed-field coils can be fashioned in any standard machine shop. The typical sensitivity of the system is better than 10−12 ergs/G, which makes a wide range of bacteria accessible to quantitative measurement of their magnetosome chains. The electronic circuits as well as the coil systems are described in detail.
TL;DR: In this article, the magnetic susceptibility of magnetotactic bacteria (MTB) culture is calculated and the model is elaborated with regard to the effect of chemotaxis for two different geometrical compositions of the experiment and the results obtained allow one to determine concentration of MTB from magnetic measurements.
Journal Article•
01 Jan 2001
TL;DR: In this paper, the magnetotactic bacteria of the loess-paleosol sequences of China as a target and made successive studies on magnetotactactic bacteria in layers of Duanjiapo section, layers of Xifeng section as well as S 5-1 layer in Luochuan section by such means as TEM, SEM, biochemical experiments, and organic geochemistry.
Abstract: The authors chose magnetotactic bacteria of the loess-paleosol sequences of China as a target and made successive studies on magnetotactic bacteria in layers of Duanjiapo section, layers of Xifeng section as well as S 5-1 layer in Luochuan section by such means as TEM, SEM, biochemical experiments, and organic geochemistry. The results show that they consist of membrane and cytoplasm as well as magnetosomes and gas balls arranged along long axes. Under the suitable conditions, a lot of magnetosomes grow in the magnetotactic bacteria. Magnetosomes consist of Fe 2O 3·H 2O, and can be discharged from the bacterial bodies to surrounding environment. This can change Fe 2+ to Fe 3+ and increase magnetic susceptibility in the layers, especially in the paleosol layers. The product of magnetotactic bacteria in the loess section of China is a function of temperature, humidity, pH value and content of iron at the surface. They are obviously different from magnetotactic bacteria in the lake and swamp in shape, quantity and arrangement of magnetosomes, and hence the magnetotactic bacteria in loessial region of Northwest China constitute a typical ecological species.