Biomineralization of a New Material by a Magnetotactic Microorganism

Abstract

Magnetotactic bacteria were first observed by R.Blakemore when studying water sediments collected in Woods Hole (Massachusetts, USA)¹. After his experimental work it was found that magnetotaxis is an orientation mechanism common to a large population of microorganisms and magnetotactic cells orient in a magnetic field, showing that the cell possesses a permanent magnetic dipole. ² This experimental evidence suggests that the magnetic detector of such organisms is composed of minerals with permanent magnetization. Electron transmission microscopy of magnetotactic cells shows the presence of electron-dense regions with dimensions ranging from 400 to 1.500nm and geometric shapes. Until now all magnetotactic bacteria analysed present small crystals of Fe₃O₄, sometimes in an ordered distribution in the interior of the cell. The identification of magnetite in the cell cytoplasm was first made using Mossbauer spectroscopy on samples of Aquaspirillum magnetotacticum but Fe₃O₄ was later found in several other species of magnetotactic bacteria. Electron microscopy studies show evidence that crystals of Fe₃O₄ are enveloped by a membrane forming the magnetosome, a specialized organelle common to all magnetotactic cells ^3–7.