IGEM:Cambridge/2008/Notebook/Magnetic Bacteria

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Aim
The aim of our project is to produce magnetic organelles in E.coli and yeast that resemble magnetosomes naturally formed in magnetotactic bacteria. We aim to engineer invaginations in E.coli with specific iron binding and mineralising proteins localised to them which carry out the functions of iron uptake and iron biomineralisation into magnetite.

Magnetosomes
Magnetosomes are inner-membrane invaginations that contain a single-domain magnetic crystal of magnetite (Fe3O4) or greigite (Fe3S4). These magnetosomes help magnetotactic bacteria to orient themselves in microaerobic conditions, and avoid oxygen-rich environments.

Applications
The ability to form small synthetic particles under closely controlled synthesis conditions.

Although small magnetic particles can be formed synthetically by following various routes, these particles are non-uniform, often not fully crystalline and compositionally nonhomogeneous. The biomineralisation route provides a way to produce highly uniform magnetite crystals without the high temperatures, pH and pressures required in industry.

Applications of magnetic cells

1. Use of magnetic bacteria for the nondestructive domain analysis of soft magnetic materials.

2. Removal of heavy metals and radionuclides from wastewater

3. Magnetic cell separation - cells containing magnetosomes can be easily manipulated by simple permanent magnets.

Applications of isolated magnetosome particles

1. Isolated magnetosomes have a large surface to volume ratio and are useful as carriers for the immobilization of large quantities of bioactive substances, which can then be separated by magnetic fields

2. Generation of magnetic antibodies - by coupling bacterial magnetite particles to antibodies to form conjugates

3. As a contrast agent for magnetic resonance imaging and tumor-specific drug carriers

Perspoectives

Although the above biotechnical potentials of bacterial magnetite have been demonstrated, no application has been exploited on a commerical scale. This is partially as a result of problems related to mass cultivation of magnetotactic behaviour/mass production of magnetic nanoparticles. We aim to tackle this problem by developing economically viable methods of production of magnetic nanoparticles in E.coli.

Process
1. The cell is grown in iron-rich media (see below) to allow iron uptake.

2. Invaginations of the inner membrane are induced by expression of the b subunit of the F1F0 ATP synthase in a mutated strain of E.coli.

3. Iron uptake into the membrane folds is mediated by the product of the Magnetospirillum magnetotacticum gene magA, which functions as a proton/iron antiporter.

4. Finally, biomineralisation is achieved by proteins encoded in the genomic 'magnetosome island' which localise to the invagination.

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Papers
http://www3.interscience.wiley.com/journal/117947251/abstract?CRETRY=1&SRETRY=0 - Paper on extraction of BMPs from magnetotactic bacteria and their use in separation of cells


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