Magnetotactic bacteria

About: Magnetotactic bacteria is a research topic. Over the lifetime, 1118 publications have been published within this topic receiving 43741 citations.

Magnetosome chains are recruited to cellular division sites and split by asymmetric septation.

Abstract: Magnetotactic bacteria navigate along magnetic field lines usingwell-ordered chains of membrane-enclosed magnetic crystals, referred toas magnetosomes, which have emerged as model to investigate organellebiogenesis in prokaryotic systems. To become divided and segregatedfaithfully during cytokinesis, the magnetosome chain has to be properlypositioned, cleaved and separated against intrachain magnetostaticforces. Here we demonstrate that magnetotactic bacteria use dedicatedmechanisms to control the position and division of the magnetosomechain, thus maintaining magnetic orientation throughout divisionalcycle. Using electron and time-lapse microscopy of synchronized cells ofMagnetospirillum gryphiswaldense, we confirm that magnetosome chainsundergo a dynamic pole-to-midcell translocation during cytokinesis.Nascent chains were recruited to division sites also indivision-inhibited cells, but not in a mamK mutant, indicating an activemechanism depending upon the actin-like cytoskeletal magnetosomefilament. Cryo-electron tomography revealed that both the magnetosomechain and the magnetosome filament are spilt into halves by asymmetricseptation and unidirectional indentation, which we interpret in terms ofa specific adaptation required to overcome the magnetostaticinteractions between separating daughter chains. Our study demonstratesthat magnetosome division and segregation is co-ordinated withcytokinesis and resembles partitioning mechanisms of other organellesand macromolecular complexes in bacteria.

Observations of Magnetosome Organization, Surface Structure, and Iron Biomineralization of Undescribed Magnetic Bacteria: Evolutionary Speculations

Abstract: Magnetotactic bacteria display one of the clearest behavioral responses to the geomagnetic field of any living organism, and are one of the few known prokaryotes which have the ability to produce intracellular biominerals. In the 15 years since they were discovered (10), these organisms have been found in environments ranging from freshwater to hypersaline, aerobic to anoxic, but usually in microaerophilic zones (6, 11, 21, 31, 50, 53, 71, 76). They are also interesting from an evolutionary aspect because structures similar to their magnetosome chains (their ‘biological bar magnets’) have been discovered in eukaryotic algae (20,72), as well as in vertebrates (46), where they may serve as part of a specialized geomagnetic sensory organelle (35,37). The fossil record of these bacteria, based on the fossilized magnetosomes, or magnetofossils (36) now extends back nearly 2 billion years into Precambrian time, prior to the earliest known eukaryotes (17,77). Hence, the presence of virtually identical magnetosome chains in the eukaryotes is consistent with an inheritance through the process of serial endosymbiosis (47). For the geosciences, the magnetic bacteria provide an important supply of fine-grained magnetite to sediments, where they are often preserved after the bacteria die (17,34,59,71). The fossil bacterial magnetosomes, termed magnetofossils by Kirschvink & Chang (36), have the same morphology (17, 51, 71, 76) and crystal structure (75) as the crystals in the living bacteria (41–45). As the sediments solidify, the magnetofossils usually align themselves with the local geomagnetic field, and thereby preserve a record of its direction. Thus, these sediments often can be used to investigate the past history of the geomagnetic field.

Magnetosomes eliminate intracellular reactive oxygen species in Magnetospirillum gryphiswaldense MSR‐1

Abstract: Summary Magnetotactic bacteria synthesize magnetic particles called magnetosomes that cause them to orient to their external magnetic fields. However, the physiological significance and other possible functions of these magnetosomes have not been explored in detail. In this study, we have investigated the biological functions of magnetosomes with respect to their ability to scavenge reactive oxygen species (ROS) in Magnetospirillum gryphiswaldense MSR-1. To assess the changes in ROS levels under different conditions, cells were cultured under aerobic or micro-aerobic conditions in medium containing high and low amounts of iron. To ensure that the observed results were not due to nonspecific interactions, reactions were carried out using a mutant deficient in synthesizing magnetite (mamO-deficient mutant), its complementary strain or the wild-type MSR-1. We observed that the levels of intercellular ROS under micro-aerobic conditions with high-iron medium were much higher when the non-synthetic Fe3O4 crystals mutant Mu21-415 was employed for the assay, compared with the wild-type or complementary strain, or when conditions were aerobic with low-iron medium. These results indicated that magnetosomes function in the scavenging of intracellular ROS. Furthermore, we have demonstrated that the magnetosomes exhibit peroxidase-like properties, by using the earlier reported in vitro horseradish peroxidase assay for artificial magnetic nanoparticles. In addition to possessing peroxidase-like activity, the magnetosomes also exhibited a more enzymatic kinetic response, suggesting that proteins on the membranes of the magnetosomes likely contribute to the enzymatic activity. This is the first study to demonstrate that magnetosomes play an important role in decreasing or eliminating ROS.

Off-axis electron holography of magnetotactic bacteria: magnetic microstructure 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.

Controlled biomineralization by and applications of magnetotactic bacteria.

Abstract: Publisher Summary The magnetotactic bacteria represent a morphologically, physiologically, and phylogenetically diverse assemblage of motile, mostly aquatic prokaryotes that passively align along geomagnetic field lines as they swim. Magnetotactic bacteria are fastidious with regard to their growth requirements and are difficult to isolate in pure culture and cultivate in the laboratory. Because of this, research in this area has been painfully slow at times. Magnetosomes are defined as intracellular crystals of a magnetic mineral surrounded by a lipid bilayer membrane. Despite their differences, the magnetotactic bacteria share several features: (1) they are Gram-negative prokaryotes phylogenetically associated with the domain bacteria, (2) they are motile by means of flagella, (3) grow only microaerophilically with oxygen or anaerobically or both, (4) with one exception possess a solely respiratory form of metabolism, (5) display nitrogenase activity and so are able to fix atmospheric dinitrogen, (6) are mesophilic with respect to growth temperatures, and (7) all possess magnetosomes.