Showing papers on "Magnetotactic bacteria published in 1980"

Ultrastructure of a magnetotactic spirillum.

Abstract: The ultrastructure of a magnetotactic bacterium (strain MS-1) was examined by transmission, scanning, and scanning-transmission electron microscopy. The organism resembled other spirilla in general cell morphology, although some differences were detected at the ultrastructural level. Electron-dense particles within magnetotactic cells were shown by energy-dispersive X-ray analysis to be localizations containing iron. A non-magnetotactic variant of strain MS-1 lacked these novel bacterial inclusion bodies. A chain of these particles traversed each magnetotactic cell in a specific arrangement that was consistent from cell to cell, seemingly associated with the inner surface of the cytoplasmic membrane. Each particle was surrounded by an electron-dense layer separated from the particle surface by an electron-transparent region. The term "magnetosome" is proposed for the electron-dense particles with their enveloping layer(s) as found in this and other magnetotactic bacteria.

South-seeking magnetotactic bacteria in the Southern Hemisphere

Abstract: Several species of aquatic bacteria which orient in the Earth's magnetic field and swim along magnetic field lines in a preferred direction (magnetotaxis) have been observed in marine and freshwater sediments of the Northern Hemisphere1,2. Their orientation is due to one or more intracytoplasmic chains of single-domain magnetite particles3. These linearly arranged particles impart a net magnetic dipole moment to the bacterium, parallel to the axis of motility. Northern Hemisphere magnetotactic bacteria with unidirectional motility swim consistently in the direction of the magnetic field, that is, to the geomagnetic North1,2,4. This implies that their magnetic dipole is systematically orientated with the North-seeking pole forward. The magnetic polarity can be reversed by single, magnetic pulses of high field strength (1–2 µs, 300–600 G), and these bacteria then swim along magnetic field lines to the South5. Due to the inclination of the Earth's magnetic field, magnetotactic bacteria which swim to the North in the Northern Hemisphere are directed downward at an angle increasing with latitude. It has been suggested that this downward-directed motion confers a biological advantage by guiding the bacteria, when dislodged, back to the sediments1. On the basis of this hypothesis, magnetotactic bacteria of the Southern Hemisphere would be expected to swim to the South to reach the bottom. We report here several morphological types of magnetotactic bacteria present in sediments of the Southern Hemisphere. These bacteria indeed swim consistently to the South, hence downward along the Earth's inclined magnetic field lines, as hypothesized. As revealed by electron microscopy, they contain internal chains of electron-opaque particles similar to those observed in magnetotactic bacteria from the Northern Hemisphere. Like their Northern Hemisphere counterparts, their magnetic polarity can be permanently reversed and they cannot be demagnetized. We also report on Northern Hemisphere magnetotactic bacteria incubated in Southern Hemisphere magnetic conditions, confirming the biological relevance of downward directed motility.

South-Seeking Magnetic Bacteria

Abstract: Magnetotactic bacteria, originally discovered by Blakemore (1975), are by far the most convincing and abundant example of magnetically sensitive organisms in existence. Their magnetite crystals passively align the bacteria with the earth's magnetic field like a 3-dimensional compass (Frankel et al. 1979). These microaerophilic bacteria normally live in the soupy, oxygen-poor mud/water transition zone in many freshwater and marine environments. If the mud is disturbed so that the bacteria are exposed to oxygen-rich water, the species discovered so far (all from the northern hemisphere) swim rapidly along the direction of magnetic north. Because the magnetic field dips downward in the northern hemisphere, the bacteria eventually reach the mud/water interface again and avoid poisoning themselves with oxygen. Moench & Konetzka (1978) have devised an elegant technique to purify the bacterial population based on their swimming response - the bacteria will swim towards the south magnetic pole of a bar magnet placed near their jar, purifying themselves into a characteristic little pellet containing millions of individual cells. (The north geographic pole is magnetically south, so the bacteria were still trying to go to the north and down.) Two major questions concerning the behaviour of these bacteria need to be answered, however: (1) which way do they swim in the southern hemisphere, and (2) what do they do on the magnetic equator where the field is horizontal?

Bulk magnetic properties of magnetotactic bacteria

Abstract: Bulk magnetization measurements at room temperature of freeze dried magnetotactic bacterial cells, nonmagnetotactic bacterial cells, and extracted magnetosomes from magnetotactic cells are presented. The role of the magnetosome in the magnetotactic response of swimming cells is discussed.

Method for generation of bio-gas

Abstract: Improved method for the production of bio-gas incorporating a magnetic field to situate magnetotactic bacteria in the reactive zone of a bio-gas producing digester.