Magnetite from magnetotactic bacteria; size distributions and twinning

Abstract

We studied intracellular magnetite particles produced by several morphological types of magnetotactic bacteria including the spirillar (helical) freshwater species, Magnetospirillum magnetotacticum, and four incompletely characterized marine strains: MV-1, a curved rodshaped bacterium; MC-1 and MC-2, two coccoid (spherical) microorganisms; and MV-4, a spirillum. Particle morphologies, size distributions, and structural features were examined using conventional and high-resolution transmission electron microscopy. The various strains produce crystals with characteristic shapes. All habits can be derived from various combinations of the isometric {111}, {110}, and {100} forms. We compared the size and shape distributions of crystals from magnetotactic bacteria with those of synthetic magnetite grains of similar size and found the biogenic and synthetic distributions to be statistically distinguishable. In particular, the size distributions of the bacterial magnetite crystals are narrower and have a distribution asymmetry that is the opposite of the nonbiogenic sample. The only deviation from ideal structure in the bacterial magnetite seems to be the occurrence of spinel-law twins. Sparse multiple twins were also observed. Because the synthetic magnetite crystals contain twins similar to those in bacteria, in the absence of characteristic chains of crystals, only the size and shape distributions seem to be useful for distinguishing bacterial from nonbiogenic magnetite.

Experimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological, paleomagnetic, and evolutionary implications

“…4 yield a mean plane separation of 43.1 ± 4.5 nm, with a center-to-center spacing of 56.8 ± 3.7 nm (1σ errors); the average interparticle gap of ~ 13.7 ± 2.1 nm is consistent with two unit membranes. This size distribution is in good agreement with the measurements of Devourd et al [39], who also did not use negative staining but had no 3-dimentional control of the chain warping. Our measured interparticle spacing, however, is significantly larger than the 10.0 nm (2 x 5.0 nm) spacing reported by Gorby et al [1], which may be a result of the negative staining procedure enhancing the apparent size of the crystals.…”

“…3 and 5 as regular truncated octahedra ('cubooctahedra' using the terminology of [39]), and the sheath as a simple cylinder surrounding the magnetosome chain. In the magnetospirilla, numerous studies have shown that the crystals tend to be aligned with their crystal axes parallel to the [111] cubic direction (i.e., they have parallel sets of {111} crystal faces perpendicular to the chain axis).…”

Magnetita biomimética mediada por proteínas del magnetosoma vs. magnetita del meteorito ALH84001: ¿Son ambas comparables?

“…Crystallographic Perfection Electron microscopy studies reveal that MTB magnetite crystals are essentially free of inner defects, with minor exceptions of {111} twinnings (Devouard et al, 1998). The crystallographic lattice lack of defects contributes to enhance the particle net magnetic moment.…”

Biomineralization: A confluence of materials science, biophysics, proteomics, and evolutionary biology

“…and observed that not only were the magnetite crystals produced by these magnetotactic bacteria of a much narrower size distribution than their abiotic cousins, they also exhibited an asymmetry in size distribution that is not observed in synthetic samples. 20 TEM analysis of magnetosomes synthesized by magnetotactic bacterium MC-1 has revealed that control over crystal structure occurs at a very early stage of crystal growth, and the medium of the culture impacts both the morphology and number of magnetite crystals, with an acetate-containing medium yielding more crystals than a sulfi de-containing medium. Such exquisite control over magnetite structure is of extreme relevance in many applications, including the development of nanotechnologybased therapeutics.…”