Iron Transport and Magnetite Crystal Formation of the Magnetic Bacterium Magnetospirillum gryphiswaldense

Magnetic bacteria are found in various morphologies as cocci, vibrios, spirilli and rods in aquatic mud layers. Magnetite (Fe3O4) is stored in phospholipid vesicles as bullet-shaped, hexagonal or cubooctahydral crystals. Size and form of these crystals are species-specific and precisely controlled. The microaerophilic Magnetospirillum gryphiswaldense forms in a near to linear chain up to 60 cubooctahedral, single domain magnetite crystals of 42-45nm diameter, which generates a magnetic dipole. Six proteins were detected in SDS-gels of the special phospholipid vesicles, which envelope the magnetite crystals. These proteins are probably involved in iron transport (FeII or/and FeIII), in nucleation catalysis, in redox or/and pH control. Iron uptake and dynamics of magnetite crystal formation were estimated simultaneously by change of light scattering of the cells within homogeneous magnetic fields. A very efficient, energy-dependent uptake of FeIII in presence of spent, iron-deficient growth medium was found. Iron uptake was tightly coupled to magnetite crystal formation and magnetisation. When FeIII was added to iron-starved cells under inducing conditions, FeIII was immediately transported into the cells and superparamagnetic crystals of less than 20nm were formed first within 30 min

Location of the basal disk and a ringlike cytoplasmic structure, two additional structures of the flagellar apparatus of Wolinella succinogenes.

The basal body of Wolinella succinogenes consists of a central rod, a set of two rings (L and P rings), a basal disk from 70 to 200 nm in diameter, and a terminal knob. In negatively stained preparations of flagellar hook-basal body complexes, some disks remain fixed perpendicularly to the grid and show that such a disk is located on the distal side of the P ring. The basal disks have been isolated with and without the P ring; in both cases there is a hole in the center of the disk. The diameter of the disk is smaller in the presence of the P ring. The L-P ring complex is therefore assumed to be a bushing for the rod. Thin sections of whole bacteria and spheroplasts reveal that the disk is attached to the inner surface of the outer membrane. At the insertions of the flagellar hook-basal body-basal disk complexes, depressions are visible in negatively stained preparations of whole bacteria and spheroplasts. A new ringlike structure is connected to an elongation of the basal body into the cytoplasm in both preparations. Its diameter (60 nm) is larger than that of the M ring. A heavily stained compartment can be seen in between the new ringlike structure and the basal disk, which may be formed by the energy transducing units

Basal-body-associated disks are additional structural elements of the flagellar apparatus isolated from Wolinella succinogenes.

The intact flagella of Wolinella succinogenes, a gram-negative, anaerobic bacterium with a single polar flagellum, were obtained by an improved procedure, introduced recently by Aizawa et al. (S.-J. Aizawa, G. E. Dean, C. J. Jones, R. M. Macnab, and S. Yamaguchi, J. Bacteriol. 161:836-849, 1985) for the flagellum of Salmonella typhimurium. Disks with a diameter of 130 +/- 30 nm, which were attached to the basal body of the isolated intact flagella, could be identified by electron microscopy as additional structural elements of the bacterial flagellar apparatus. In freeze-dried and metal-shadowed samples, two rings of the basal body were detected on one side and a terminal knob was located on the other side of the disks. Suspension of the flagellar apparatus in acidic solution dissociated the flagellar filaments, yielding hook-basal body complexes with and without the associated disks. If whole cells were subjected to low pH, double disks of the same diameter and with a central hole of about 13 nm could be isolated. Similar parallel disks could be seen also in negatively stained whole cells. When uranyl acetate was used for negative staining of the intact flagella, concentric rings were detected on the disks, similar to the concentric membrane rings found by Coulton and Murray (J. W. Coulton and R. G. E. Murray, J. Bacteriol. 136:1037-1049, 1978) on platelike arrays of proteins in outer membrane preparations of Aquaspirillum serpens. Because the disks of W. succinogenes can be isolated together with the flagellar hook-basal body complex, they appear to be basal-body-rather than secondary membrane-associated structures. It is possible that these disks are the bearing or stator of this rotary device