Magnetotactic bacteria

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

Magnetosome chain arrangement and stability in magnetotactic cocci

Abstract: We have studied the disposition of chains of magnetosomes inside magnetotactic cocci with light and electron microscopy. Light microscopy of isolated cocci indicated that the chains of magnetosomes are disposed on opposite sides of the cell. Electron spectroscopic imaging of whole unprocessed bacteria, showed the magnetosome chains in the cells. Freeze-etching of the cell surface allowed the observation of the close association of the chain with the cell surface. During the replication process of the freeze-etching, the magnetosome chains remained attached to the replicas, which indicates that chains were very close to the cell surface before freezing. We provide evidence that the large area of the contact faces between magnetosomes in a chain may provide an extra mechanical stability that helps keep the magnetosomes in chains even after isolation from the bacteria. Comparison with pointed magnetosomes from different cocci present in the same samples showed that the maintenance of linear chains is more difficult to be achieved because of the geometry of the crystals.

Structure and evolution of the magnetochrome domains: no longer alone.

Abstract: Magnetotactic bacteria (MTB) can swim along Earth’s magnetic field lines, thanks to the alignment of dedicated cytoplasmic organelles. These organelles, termed magnetosomes, are proteolipidic vesicles filled by a 35-120 nm crystal of either magnetite or greigite. The formation and alignment of magnetosomes are mediated by a group of specific genes, the mam genes, encoding the magnetosome-associated proteins. The whole process of magnetosome biogenesis can be divided into four sequential steps; (i) cytoplasmic membrane invagination, (ii) magnetosomes alignment, (iii) iron crystal nucleation and (iv) species-dependent mineral size and shape control. Since both magnetite and greigite are a mix of iron(III) and iron(II), iron redox state management within the magnetosome vesicle is a key issue. Recently, studies have started pointing out the importance of a MTB-specific c-type cytochrome domain found in several magnetosome-associated proteins (MamE, P, T and X). This magnetochrome (MCR) domain is almost always found in tandem, and this tandem is either found alone (MamT), in combination with a PDZ domain (MamP), a domain of unknown function (MamX) or with a trypsin combined to one or two PDZ domains (MamE). By taking advantage of new genomic data available on MTB and a recent structural study of MamP, which helped define the MCR domain boundaries, we attempt to retrace the evolutionary history within and between the different MCR-containing proteins. We propose that the observed tandem repeat of MCR is the result of a convergent evolution and attempt to explain why this domain is rarely found alone.

MS-1 magA Revisiting Its Efficacy as a Reporter Gene for MRI

Abstract: Bacterial genes involved in the biomineralization of magnetic nanoparticles in magnetotactic bacteria have recently been proposed as reporters for magnetic resonance imaging (MRI). In such systems,...

Biomineralization of a New Material by a Magnetotactic Microorganism

Abstract: Magnetotactic bacteria were first observed by R.Blakemore when studying water sediments collected in Woods Hole (Massachusetts, USA)1. After his experimental work it was found that magnetotaxis is an orientation mechanism common to a large population of microorganisms and magnetotactic cells orient in a magnetic field, showing that the cell possesses a permanent magnetic dipole. 2 This experimental evidence suggests that the magnetic detector of such organisms is composed of minerals with permanent magnetization. Electron transmission microscopy of magnetotactic cells shows the presence of electron-dense regions with dimensions ranging from 400 to 1.500nm and geometric shapes. Until now all magnetotactic bacteria analysed present small crystals of Fe3O4, sometimes in an ordered distribution in the interior of the cell. The identification of magnetite in the cell cytoplasm was first made using Mossbauer spectroscopy on samples of Aquaspirillum magnetotacticum but Fe3O4 was later found in several other species of magnetotactic bacteria. Electron microscopy studies show evidence that crystals of Fe3O4 are enveloped by a membrane forming the magnetosome, a specialized organelle common to all magnetotactic cells 3–7.