Showing papers on "Magnetotactic bacteria published in 1979"

Magnetite in Freshwater Magnetotactic Bacteria

Abstract: A previously undescribed magnetotactic spirillum isolated from a freshwater swamp was mass cultured in the magnetic as well as the nonmagnetic state in chemically defined culture media. Results of Mossbauer spectroscopic analysis applied to whole cells identifies magnetite as a constituent of these magnetic bacteria.

Isolation and pure culture of a freshwater magnetic spirillum in chemically defined medium.

Abstract: A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp. The organism was cultured in a chemically defined medium containing ferric quinate and succinate as sources of iron and carbon, respectively. Nonmagnetic variants of this isolate were maintained in chemically defined medium lacking ferric quinate. In contrast to magnetic cells, these had less iron and lacked measurable magnetic remanence and the intracytoplasmic crystals. In other respects, including moles percent guanine plus cytosine content, growth characteristics, nutrition, and physiology, the two types were similar. The isolate reduced nitrate without accumulating nitrite and produced ammonia during growth. Nitrate or ammonium ions served as a nitrogen source. The organism was microaerophilic and did not grow anaerobically with nitrate in the medium. In chemically defined medium, cells synthesized magnetite only if the initial O2 concentration in the atmosphere of sealed cultures was 6% (vol/vol) or less.

Ferromagnetism in Freshwater Bacteria

Abstract: Magnetotactic bacteria isolated from swamp water were grown in pure culture in the laboratory. This newly isolated species was cultured in the magnetic and the nonmagnetic state. Magnetic cells, which were rich in iron, also produced particles similar to those found previously in other magnetic bacteria of marshes and bogs. By contrast, their nonmagnetic counterparts had much lower iron levels and lacked the crystal structures. Mossbauer spectroscopic analyses of whole cells of magnetic bacteria indicated that they contained the mineral magnetite. Morphologically diverse magnetotactic bacteria (Fig. 1'1' J,~. normally (Blakemore, present in marine and freshwater f environments kemOl: 1975) aligned with, and swam in a preferred direction in, the geomagnetic field (Kalmijn and Blakemore, 1977). Most of the cells observed in northward various mud samples swim and downward. Reversal of the ambient magnetic field with a small permanent magnet (Fig. 2) or with Helmholtz coils (Kalmijn and Blakemore, 1977) caused the swimming cells to make large U-turns within seconds and swim in the opposite direction. Killed cells also oriented in uniform magnetic fields as low as 0.1 G (1 G = 10-4 T). studies, As a result of cell remagnetization U i Kalmijn and Blake­ more (1978; see also Scientific American, 1978, 238: 72-73)

Magnetic Effects on Lower Organisms

Abstract: Bacteria that orient and swim in a preferred direction in magnetic fields have been observed in diverse aquatic environments.1 These magnetotactic bacteria include a variety of morphologically distinct forms. Kalmijn and Blakemore2 found that these bacteria orient in uniform magnetic fields of about 0.5 G. Reversal of the geomagnetic field with Helmholtz coils caused the swimming bacteria to turn around in large U-turns and swim in the opposite direction. Killed bacteria also orient to align with imposed magnetic fields. Richard Blakemore