Magnetospirillum are motile bacteria that thrive in low oxygen environments and produce magnetic nanocrystals for navigation. This article details the culturing methods and experimental setups to study their magnetotactic behavior.
Magnetospirillum are motile bacteria that thrive in low oxygen.
They produce magnetic nanocrystals that act as magnetic dipoles, helping them navigate the geomagnetic field toward an optimal oxygen concentration.
To culture Magnetospirillum, take oxygen-free liquid media. Inject a controlled volume of oxygen to establish microaerobic conditions, add bacteria, and incubate.
Over time, turbidity increases, indicating bacterial growth.
To prepare a semi-solid culture, use a medium containing a pink oxygen indicator that becomes colorless in the low-oxygen zone, marking the oxic-anoxic interface (OAI) with an optimal
oxygen concentration.
Inoculate the bacteria at the OAI, seal the tube, and incubate.
The bacteria multiply to form a band that migrates upward as oxygen is consumed.
To assess magnetotactic behavior, prepare a hanging drop of the cultured bacteria and place a magnet near it.
Under a microscope, observe directional swimming toward the magnet and reversal of movement when the magnet is flipped.
To inoculate strains MSR-1, AMB-1, and MS-1 in liquid medium, flame the tops of the oxygen and fresh medium bottles by applying ethanol on the stoppers and passing them through the flame of a Bunsen burner.
Using a sterile syringe and a needle, extract one milliliter of oxygen from the oxygen bottle and transfer it into the fresh medium bottle. If using the inoculum from another culture grown in a glass bottle, flame both bottles. Then inoculate one milliliter of the older culture into the fresh medium.
Incubate the culture at 32 degrees Celsius, and inoculate it into fresh medium after four to seven days. To inoculate MSR-1 in oxygen gradient, semisolid medium, verify that the tube of fresh medium displays a well-defined OAI, materialized by a pink to colorless interface about one to three centimeters below the surface of the medium. If the inoculum is coming from another oxygen concentration gradient semisolid culture, harvest the bacteria by aspirating 50 microliters of the culture with a sterile pipette tip placed on the band formed by the bacteria.
Slowly inoculate these bacteria at the OAI in the fresh medium, avoiding disturbing the interface. Seal the tube and let the bacteria grow between 25 degrees Celsius and 30 degrees Celsius. To ensure that the bacteria are both magnetic and modal, place a drop of culture on microscope cover slip.
Flip the cover slip, and install it on an O-ring resting on a glass slide. Ensure that the drop does not touch the bottom slide. Place the hanging drop under a microscope and focus on an edge of the droplet.
Place the south pole of a magnet close to that edge, and watch the bacteria swim towards the edge. Flip the magnet to make them swim in the opposite direction.
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