Showing papers on "Magnetotactic bacteria published in 2003"

Characterization of a Spontaneous Nonmagnetic Mutant of Magnetospirillum gryphiswaldense Reveals a Large Deletion Comprising a Putative Magnetosome Island

Abstract: Frequent spontaneous loss of the magnetic phenotype was observed in stationary-phase cultures of the magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1. A nonmagnetic mutant, designated strain MSR-1B, was isolated and characterized. The mutant lacked any structures resembling magnetosome crystals as well as internal membrane vesicles. The growth of strain MSR-1B was impaired under all growth conditions tested, and the uptake and accumulation of iron were drastically reduced under iron-replete conditions. A large chromosomal deletion of approximately 80 kb was identified in strain MSR-1B, which comprised both the entire mamAB and mamDC clusters as well as further putative operons encoding a number of magnetosome-associated proteins. A bacterial artificial chromosome clone partially covering the deleted region was isolated from the genomic library of wild-type M. gryphiswaldense. Sequence analysis of this fragment revealed that all previously identified mam genes were closely linked with genes encoding other magnetosome-associated proteins within less than 35 kb. In addition, this region was remarkably rich in insertion elements and harbored a considerable number of unknown gene families which appeared to be specific for magnetotactic bacteria. Overall, these findings suggest the existence of a putative large magnetosome island in M. gryphiswaldense and other magnetotactic bacteria.

Magnetotactic Bacteria on Earth and on Mars

Abstract: Continued interest in the possibility of evidence for life in the ALH84001 Martian meteorite has focused on the magnetite crystals. This review is structured around three related questions: is the magnetite in ALH84001 of biological or non-biological origin, or a mixture of both? does magnetite on Earth provide insight to the plausibility of biogenic magnetite on Mars? could magnetotaxis have developed on Mars? There are credible arguments for both the biological and non-biological origin of the magnetite in ALH84001, and we suggest that more studies of ALH84001, extensive laboratory simulations of non-biological magnetite formation, as well as further studies of magnetotactic bacteria on Earth will be required to further address this question. Magnetite grains produced by bacteria could provide one of the few inorganic traces of past bacterial life on Mars that could be recovered from surface soils and sediments. If there was biogenic magnetite on Mars in sufficient abundance to leave fossil remains in the volcanic rocks of ALH84001, then it is likely that better-preserved magnetite will be found in sedimentary deposits on Mars. Deposits in ancient lakebeds could contain well-preserved chains of magnetite clearly indicating a biogenic origin.

Envelope ultrastructure of uncultured naturally occurring magnetotactic cocci.

Abstract: Magnetotactic bacteria are microorganisms that respond to magnetic fields. We studied the surface ultrastructure of uncultured magnetotactic cocci collected from a marine environment by transmission electron microscopy using freeze-fracture and freeze-etching. All bacteria revealed a Gram-negative cell wall. Many bacteria possessed extensive capsular material and a S-layer formed by particles arranged with hexagonal symmetry. No indication of a metal precipitation on the surface of these microorganisms was observed. Numerous membrane vesicles were observed on the surface of the bacteria. Flagella were organized in bundles originated in a depression on the surface of the cells. Occasionally, a close association of the flagella with the magnetosomes that remained attached to the replica was observed. Capsules and S-layers are common structures in magnetotactic cocci from natural sediments and may be involved in inhibition of metal precipitation on the cell surface or indirectly influence magnetotaxis.

Biological permanent magnets

Abstract: Magnetotactic bacteria orient and migrate along magnetic field lines. Each cell is essentially a self-propelled magnetic dipole. The magnetic properties of these bacteria have been determined by a variety of techniques, including pulsed hysteresis measurements on single cells.

Magnetic force driven orientation of Co23B10 arrays inspired by magnetotactic bacteria

Abstract: Ordered submicron ferromagnetic Co–B arrays were obtained through a biomimetic process at ambient temperature. When Co2+ ions complexed to soluble starch were reduced by potassium borohydride in a magnetic field, the magnetic force allowed the nanoparticles of Co–B alloys to array along the field lines and deposit on a solid support. This process is inspired by the migration mechanism of magnetotactic bacteria in a geomagnetic field and this convenient strategy should be helpful for the production of ordered arrays of other magnetic materials. After Co–B alloys are assembled into ordered chains, they exhibit strong ferromagnetic signals in the variable temperature ferromagnetic resonance spectra in the temperature range of 100–420 K.

Crystallization of NaCl and CaCO3 from Solution Using Magnetotactic Bacteria as Laser Beam Energy Absorbers under the Optical Tweezers Microscope

Abstract: Magnetotactic bacteria are motile microorganisms presenting intracellular membrane-bounded magnetic crystals, usually composed of magnetite (Fe3O4). These structures function as magnetic compass orienting the whole organism along magnetic field lines [1]. When trying to catch marine magnetotactic bacteria with the optical tweezers, we noted that, surprisingly, the laser beam killed the bacteria. Focusing the laser onto magnetotactic bacteria concentrated in the border of a drop of water caused “explosions” as if the water was locally boiling (fig. 1) and/or the formation of salt crystals from seawater. Then, we decided to study the crystallization of NaCl and CaCO3 induced by the laser beam of the optical tweezers directed towards magnetically isolated uncultured marine magnetotactic bacteria.