How to Isolate Magnetotactic Bacteria

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Magnetotactic bacteria form magnetite crystals (Fe3O4) inside their cells that allow them to utilize the Earths’ magnetic field for orientation within water columns and water saturated sediments. Once aligned, the bacteria can then efficiently swim along the field lines to find their optimal oxygen concentrations. Magnetite produced within these bacteria is of high industrial and commercial value and can be harvested for its properties. To isolate magnetotactic bacteria, Pasteur pipettes were filled with media and then melted closed on one end, creating magnetotactic “race-tracks”. Sample sediment slurry was aliquoted into the open end of the sterile pipette “race-track”, which was then laid between two aligned magnets. The magnetotactic bacteria migrated along the magnetic field lines to the tip of the pipette, which was subsequently broken off with the aggregation of magnetotactic bacteria being extracted and transferred to an oxygen-sulfide gradient slush agar tube. After incubation, distinctive bands formed in the gradient media, corresponding to different species’ oxygen requirements. Gradient tubes were then sterilely cracked open, their slush agar plugs were extruded, and individual magnetotactic bands were excised with sterile razor blades. The “race-track” and oxygen tube gradient method demonstrated here, allow for the isolation of magnetotactic bacteria.