Showing papers on "Magnetotactic bacteria published in 2005"

Complete Genome Sequence of the Facultative Anaerobic Magnetotactic Bacterium Magnetospirillum sp. strain AMB-1

Abstract: Magnetospirillum sp. strain AMB-1 is a Gram-negative a-proteobacterium that synthesizes nano-sized magnetites, referred to as magnetosomes, aligned intracellularly in a chain. The potential of this nano-sized material is growing and will be applicable to broad research areas. It has been expected that genome analysis would elucidate the mechanism of magnetosome formation by magnetic bacteria. Here we describe the genome of Magnetospirillum sp. AMB-1 wild type, which consists of a single circular chromosome of 4 967 148 bp. For identification of genes required for magnetosome formation, transposon mutagenesis and determination of magnetosome membrane proteins were performed. Analysis of a non-magnetic transposon mutant library focused on three unknown genes from 2752 unknown genes and three genes from 205 signal transduction genes. Partial proteome analysis of the magnetosome membrane revealed that the membrane contains numerous oxidation/reduction proteins and a signal response regulator that may function in magnetotaxis. Thus, oxidation/reduction proteins and elaborate multidomain signaling proteins were analyzed. This comprehensive genome analysis will enable resolution of the mechanisms of magnetosome formation and provide a template to determine how magnetic bacteria maintain a species-specific, nanosized, magnetic single domain and paramagnetic morphology.

Combined Approach for Characterization of Uncultivated Magnetotactic Bacteria from Various Aquatic Environments

Abstract: Both magnetic collection and "race track" purification techniques were highly effective for selective enrichment of magnetotactic bacteria (MTB) from complex communities, as suggested by amplified ribosomal DNA restriction analysis and denaturing gradient gel electrophoresis combined with sequence analysis of 16S rRNA genes. Using these purification methods, the occurrence and diversity of MTB in microcosms from various marine and freshwater environments were assayed by using a combined microscopic, molecular, and cultivation approach. Most microcosms were dominated by magnetotactic cocci. Consistently, the majority of retrieved 16S RNA sequences were affiliated with a distinct cluster in the Alphaproteobacteria. Within this lineage the levels of sequence divergence were <1 to 11%, indicating genus-level diversity between magnetotactic cocci from various microcosms, as well as between MTB from different stages of succession of the same microcosms. The community composition in microscosms underwent drastic succession during incubation, and significant heterogeneities were observed between microcosms from the same environmental sources. A novel magnetotactic rod (MHB-1) was detected in a sediment sample from a lake in northern Germany by fluorescence in situ hybridization. MHB-1 falls into the Nitrospira phylum, displaying 91% 16S rRNA sequence similarity to "Magnetobacterium bavaricum." In extensive cultivation attempts, we failed to isolate MHB-1, as well as most other MTB present in our samples. However, although magnetotactic spirilla were not frequently observed in the enrichments, 10 novel isolates of the genus Magnetospirillum which had not routinely been isolated in pure culture before were obtained.

Crystal-size and shape distributions of magnetite from uncultured magnetotactic bacteria as a potential biomarker

Abstract: We studied the sizes and shapes of magnetite nanocrystals produced by several types of uncultured magnetotactic bacteria to understand whether their size distributions can be used for identifying the biogenic origin of magnetite crystals in geological samples. The two-dimensional projections of the crystals were measured on transmission electron microscope (TEM) images, and features of crystal-size and shape-factor distributions (CSD and SFD, respectively) were analyzed. In agreement with previous results, most magnetite CSD curves are asymmetric and negatively skewed; however, one magnetotactic strain produced particles that have a normal size distribution. A statistical analysis of CSDs and SFDs (both from this and previous studies) reveals similarities among magnetite from magnetotactic strains from various locations. In particular, crystals in a cultured marine strain (MC-2) were indistinguishable from magnetite from a freshwater strain. We tested whether CSDs of distinct magnetosome types can be recovered from the shape and size data of all particles combined in samples that contain several types of magnetosomes; such samples can be used as models for rocks that contain magnetite nanocrystals of unknown and, presumably, various origins. If the SFDs of the distinct magnetosome types occurring in the same sample differ, the CSDs of individual magnetosome types can be retrieved from bulk data. In such cases the characteristic shape of the size distribution can be used for identifying magnetite as originating from magnetotactic bacteria.

Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the Verwey transition using electron holography

Abstract: Off-axis electron holography in the transmission electron microscope is used to record magnetic induction maps of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the sample using liquid nitrogen. The magnetic microstructure is related to the morphology and crystallography of the particles, and to interparticle interactions. At room temperature, the magnetic signal is dominated by interactions and shape anisotropy, with highly parallel and straight field lines following the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction undulates along the length of the chain. This behaviour may result from a competition between interparticle interactions and an easy axis of magnetisation that is no longer parallel to the chain axis. The quantitative nature of electron holography also allows the change in magnetisation in the crystals with temperature to be measured.

Bacterial magnetite produced in water column dominates lake sediment mineral magnetism: Lake Ely, USA

Abstract: SUMMARY Environmental magnetic studies of annually laminated sediments from Lake Ely, northeastern Pennsylvania, USA indicate that bacterial magnetite is the dominant magnetic mineral in the lake sediment. In previous studies of Lake Ely sediment, the dark, organic-rich layers in the annual laminae were interpreted to have high-intensity saturation isothermal remanent magnetizations (SIRMs) while the light-coloured, silt-rich layers have low-intensity SIRMs. To test the hypothesis that the magnetic grains in the sediments were an authigenic product of magnetotactic bacteria rather than detrital magnetic grains eroded from the watershed, we analysed samples from the water column, the lake sediment, and a sediment trap installed near the lake bottom. Direct microscopic observation of the water column samples showed the presence of magnetotactic bacteria in and below the oxic-anoxic transition zone (OATZ). To characterize the magnetic minerals, rock magnetic parameters were measured for material from the water column, the sediment trap and the dark- and light-coloured lake sediments. Low-temperature magnetic measurements tested for the presence of magnetosomes in separated dark- and light-coloured layer samples. Numeric unmixing of the low-temperature results showed that biogenic magnetites were present in the lake sediment and contributed more significantly to the SIRM in the dark, organic-rich layers than in the light-coloured, inorganic silt-rich layers. Observations under the transmission electron microscope (TEM) of magnetic extracts also show the abundance of magnetosomes in the lake sediment. The presence of live magnetotactic bacteria in the water column and the predominance of bacterial magnetites in filtered particulate matter, sediment traps and recent lake sediment all suggest that bacterial magnetites are the main magnetic minerals in Lake Ely sediment. This finding suggests that changes in environmental factors that control the productivity of magnetic bacteria in the lake likely contribute to the variability of magnetic mineral concentrations observed in the lake sediments.

Habits of Magnetosome Crystals in Coccoid Magnetotactic Bacteria

Abstract: High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control.

Intracellular inclusions of uncultured magnetotactic bacteria

Abstract: Magnetotactic bacteria produce magnetic crystals in organelles called magnetosomes. The bacterial cells may also have phosphorus-containing granules, sulfur globules, or polyhydroxyalkanoate inclusions. In the present study, the ultrastructure and elemental composition of intracellular inclusions from uncultured magnetotactic bacteria collected in a marine environment are described. Magnetosomes contained mainly defect-free, single magnetite crystals with prismatic morphologies. Two types of phosphorus-containing granules were found in magnetotactic cocci. The most common consisted of phosphorus-rich granules containing P, O, and Mg; and sometimes also C, Na, Al, K, Ca, Mn, Fe, Zn, and small amounts of S and Cl were also found. In phosphorus-sulfur-iron granules, P, O, S, Na, Mg, Ca, Fe, and frequently Cl, K, and Zn, were detected. Most cells had two phosphorus-rich granules, which were very similar in elemental composition. In rod-shaped bacteria, these granules were positioned at a specific location in the cell, suggesting a high level of intracellular organization. Polyhydroxyalkanoate granules and sulfur globules were less commonly seen in the cells and had no fixed number or specific location. The presence and composition of these intracellular structures provide clues regarding the physiology of the bacteria that harbor them and the characteristics of the microenvironments where they thrive. [Int Microbiol 2005; 8(2):111-117]

Gold and Silver Trapping by Uncultured Magnetotactic Cocci

Abstract: We studied the sites of gold and silver trapping by uncultured magnetotactic cocci from microcosms using transmission electron microscopy and energy-dispersive X-ray analysis. Two morphotypes were found to trap gold or silver. Morphotype 1 had large magnetite crystals frequently twinned in an unusual way and contained phosphorus-rich granules and electron-lucent inclusions probably composed of polyhydroxyalkanoates. Morphotype 2 presented smaller crystals with smaller width/length ratios and granules containing C, O, P, S, Cl, Na, Mg, Ca, and Fe, called phosphorus-sulfur-iron granules due to the presence of relatively large amounts of phosphorus, sulfur and iron. Gold was found in morphotype 2 bacteria, mainly in phosphorus-sulfur-iron granules. Additionally, the capsule presented small deposits that seemed to be composed of elemental gold. Silver was found in both spherical and rosette-shaped crystalline deposits also containing sulfur at the cell envelope of morphotype 1 bacteria. The rosette-shaped dep...

Method and system for controlling micro-objects or micro-particles

Abstract: Moving components with dimensions much smaller than what micro-electro-mechanical system (MEMS) technology can accomplish in terms of force generated and power efficiency, are integrated onto micro-systems. These moving components referred to herein as “bio-components” are special bacteria (magnetotactic bacteria) where the motion of these bio-components can be controlled by generating an “artificial pole” by a magnetic field generated by a constant electrical current that can be varied to change the location of the “artificial pole” from an electrical system such as an embedded electronic micro-circuit. According to the present invention, it is possible through a software program or codes, to control the direction of motion of these magnetotactic bacteria, for example, by downloading such program onto the embedded electronics (controller or the like), and to generate the required magnetic field to control such bacteria to accomplish a particular task. Moreover, though integrated sensory means and new algorithms, the magnetotactic bacteria-based system could adapt or change the direction of motion from new occurring conditions.

Magnetic capture of a single magnetic nanoparticle using nanoelectromagnets

Abstract: We demonstrate the fabrication of nanoelectromagnets and the magnetic capture of a single magnetic nanoparticle. The magnetic nanoparticles are extracted from magnetotactic bacteria and their diameter is approximately 50 nm. We show that a single nanoparticle is captured at each corner of the serpentine-shaped nanoelectromagnet, and the maximum magnetic field of 35 mT (and the maximum magnetic-field gradient of 4×105T∕m) is shown to be created at the capture spots of the nanoelectromagnet. It is also shown that there is a crossover between the magnetic force and the diffusion force at several hundred nm away from the magnet. This distance is comparable to the average interparticle distance.

Detection and function of biogenic magnetite

Abstract: Magnetite is a widespread accessory mineral in rocks and soils. As was first shown by Lowenstam (1962), magnetite frequently forms also by biochemical processes, with varying degrees of control of the organisms over the mineralization process. Lowenstam distinguishes between biologically induced (BIM) and biologically controlled mineralization(BCM). The former refers to processes with no biological control, and the later to processes with strict metabolic and genetic control. In this thesis, two examples of biogenic magnetite with eminently different magnetic properties are studied. One is magnetite as found in so-called magnetotactic bacteria; the second example is magnetite as identi¯ed in tissue of pigeon's heads. In the first part of this work, the results of a series of rock magnetic measurements on concentrated samples of pure magnetotactic bacteria will be presented. These bacteria offer a unique opportunity to study the process of biologically controlled mineralization, since these organisms synthesize intracellular particles of magnetite or greigite arranged in chains, that give the bacterium the characteristic property of a swimming compass needle. The magnetic crystals, so-called magnetosomes, are magnetically speaking stable single-domain particles, characterized by a size such that the particles have minimum induced magnetization and maximum permanent magnetic moment (i.e. particle size between 30 and 130 nm). The bacteria studied here have been harvested in sediments from lake Chiemsee. They were extracted from the sediments and concentrated to an extent that enabled a detailed characterization by macroscopic magnetic measurements. The so-called Bacteriodrome was used to concentrate samples of approximately 10E7 cells. Different magnetic criteria, aiming to specifically identify bacterial magnetite in sediments, have been tested, including: (1) acquisition and demagnetization of isothermal remanent magnetization (IRM); (2) acquisition of anhysteretic remanent magnetization and (3) thermal dependence of low temperature saturation IRM, after cooling in zero field (ZFC) or in a 2.5 T field (FC) from 300 to 5 K. The best method turns out to be the so-called delta-delta test (dFC/dZFC), first proposed by Moskowitz et al. (1993), and based on the low temperature variation of the SIRM, measured both in a strong field (FC) and in zero field (ZFC). At the Verwey transition (ca. 120 K) the d-value for each curve is determined and the d-ratio (dFC/dZFC) calculated. Values exceeding 2, are indicators for the presence of chains of stable single-domain particles, which form only under strict biological control. However, it is shown that the suitability of rock magnetic techniques to detect and characterize biogenic magnetite in bulk, natural samples such as lake sediments is still limited, due to diagenetic processes and the occurrence of other non-biogenic magnetic minerals, which blur the distinct magnetic properties of the former. The only certain proof for bacterial magnetite is the optical identification -although time consuming and tedious- by Transmission Electron Microscopy. The magnetite inclusions found in pigeon tissue are very different in their magnetic properties with respect to bacterial magnetite. With their small grain size (between 2 and 10 nm), these particles fall within the superparamagnetic size range and are characterized by a large induced magnetization and no permanent magnetic moment. The pigeon magnetite is concentrated in spherical clusters of approximately 1-3 micrometers in diameter. The response of these clusters to magnetic fields has been simulated by spherules of ferrofluid. Depending on their geometrical arrangement these spherules show peculiar magnetic properties. Based on these properties, three models have been developed experimentally and theoretically with respect to a possible application as biological sensory elements. The magnetic properties of the sensory models are tested in the light of behavioral experiments conducted in the past on homing pigeons and migratory birds. In these experiments, the birds were exposed to defined magnetic fields to specifically affect a magnetite-based magnetoreceptor. As will be seen, most of the responses of the birds observed in the behavioral experiments can be explained by simulating the effects of these magnetic treatment on ferrofluid spherules.

Extraction of Magnetosome from Acidthiobacillus ferrooxidans

Abstract: In physiological property and growing environment aspects, there are some similarities betweenAcidthiobacillus ferrooxidans（ATF） and magnetotactic bacteria. ATF shows magnetotacxis under the microscope. Themagnetosome can be extracted from ATF by using the extracting method of magnetosome from magnetotactic bacteria.The membrane of ATF was crushed by ultrasonic wave and the magnetosomes in the ATF which mainly contains Fethrough chemical detection were attracted by using magnetite. After purifing with sucrose density gradient centrifugationand washing by PBS, the magnetosomes can be seen clearly through a transmission electron microscope. The resultsindicate there are a small amount of intracellular magnetosomes which made the ATF be magnetotactic under the applied magnetic field. It is the first time to find that ATF was magnetotactic. The magnetotaxis of ATF can be utilizedand isolated by the magnetotactic properties to gain the high - performance ATF strains of mineral leaching, whichhave high activity and different magnetism.

Extraction of Magnetosomes from Acidthiobacillus ferrooxidans

Abstract: There are many similarities between Acidthiobacillus ferrooxidans (At.f) and magnetotactic bacteria on physiological properties and growing environment except their trophic types. Magnetosomes can be extracted from At.f by using an improved extracting method of magnetosomes. The membrane of At.f was crushed by ultrasonic wave and the magnetosomes in At.f which mainly contains Fe through chemical detection were attracted by using magnetite. After purified with sucrose density gradient centrifugation and washing by PBS and ethanol, 0.8mg/l magnetosomes were obtained. The magnetosomes were clearly observed under a transmission electron microscope (TEM). The results indicate there are a small amount of intracellular magnetosomess which made At.f weak magnetotactic under the applied magnetic field. At.f can be isolated by using the magnetotactic property for biohydrometallurgy and the high effective At.f strain can be

GJI Geomagnetism, rock magnetism and palaeomagnetism Bacterial magnetite produced in water column dominates lake sediment mineral magnetism: Lake Ely, USA

Abstract: SUMMARY Environmental magnetic studies of annually laminated sediments from Lake Ely, northeastern Pennsylvania, USA indicate that bacterial magnetite is the dominant magnetic mineral in the lake sediment. In previous studies of Lake Ely sediment, the dark, organic-rich layers in the annual laminae were interpreted to have high-intensity saturation isothermal remanent magnetizations (SIRMs) while the light-coloured, silt-rich layers have low-intensity SIRMs. To test the hypothesis that the magnetic grains in the sediments were an authigenic product of magnetotactic bacteria rather than detrital magnetic grains eroded from the watershed, we analysed samples from the water column, the lake sediment, and a sediment trap installed near the lake bottom. Direct microscopic observation of the water column samples showed the presence of magnetotactic bacteria in and below the oxic-anoxic transition zone (OATZ). To characterize the magnetic minerals, rock magnetic parameters were measured for material from the water column, the sediment trap and the dark- and light-coloured lake sediments. Lowtemperature magnetic measurements tested for the presence of magnetosomes in separated dark- and light-coloured layer samples. Numeric unmixing of the low-temperature results showed that biogenic magnetites were present in the lake sediment and contributed more significantly to the SIRM in the dark, organic-rich layers than in the light-coloured, inorganic silt-rich layers. Observations under the transmission electron microscope (TEM) of magnetic extracts also show the abundance of magnetosomes in the lake sediment. The presence of live magnetotactic bacteria in the water column and the predominance of bacterial magnetites in filtered particulate matter, sediment traps and recent lake sediment all suggest that bacterial magnetites are the main magnetic minerals in Lake Ely sediment. This finding suggests that changes in environmental factors that control the productivity of magnetic bacteria in the lake likely contribute to the variability of magnetic mineral concentrations observed in the lake sediments.

STUDY ON ABSORPTION Ni~(2+)BY MTB AND MAGNETIC FIELD

Abstract: Biosorption of Ni2+ was carried out using MTB (magnetotactic bacteria) and magnetic field, and the effect of performance parameters such as pH, T ( ℃) , sorption duration on it, intensity of magnetic field and the place of wire casing were analyzed. No significant effect of temperature has been observed in the test, while other factor exerted important influence on the sorption process.

Long Magnetic Nanochains Assembled by Magnetotactic Bacteria in a Directional Field

Abstract: A new species of single-cell magnetotactic bacteria, the NMV-1 bacteria, has been found by us. Each NMV-1 bacterium synthesizes itself a chain of magnetic nanoparticles inside its body. When an external magnetic field is applied, long bacteria chains come into being in the direction of the field in the water. More than 30 µm long chains of live bacteria have been observed. Length of bacteria chains is field dependant: the higher the magnetic field is, the longer the bacteria chains are. The bacteria chains orientation is controllable and the chains can be stably trapped. The mechanism of the assembly of long bacteria chains is also discussed. The results show that, while an external magnetic field is applied, the NMV-1 bacteria have strong enough interactions between each other to assemble long bacteria chains. After positioning the bacteria chain, cellular membranes of the bacteria were removed by cell lysis, leaving long chains of magnetic nanoparticles on a substrate. These magnetic nanochains can be potentially used as building blocks for magnetic nanostructures.