Hunting for Magnetotactic Bacteria

There are a few pointers that might be useful for obtaining good enrichments of magnetotactic bacteria. First, try and collect from the north side of the pond! I know this seems silly, but in a closed basin, like a pond, they do wind up in greater numbers there. Magnetotactic bacteria need the aerobic/anaerobic interface. The aerobic/anaerobic interface in ponds is typically within the first few centimeters or so of sediment (unless there is an unusually heavy load of organics, like agricultural run off or a large population of water fowl, in which it would be closer to the surface). Make sure you are using the correct end of the magnet if it's not marked! The bacteria will be attracted to the end of a stir bar that attracts the north-pointing needle of the compass. To observe the bacteria take a drop of the surface sediment and place it on a microscope slide, place a drop of clear pond water next to the drop of sediment, then place the magnetic to the side of the water drop so that the bacteria swim out of the sediment into the clear water. Keep looking for the bacteria to collect at the edge of the water drop closest to the magnetic. A dissecting scope (or a low powered microscope) with dark field illumination should do the trick for observing them. To observe them at higher magnification, you can make a modified hanging drop slide. Place two pieces of labeling tape on the glass slide to raise the cover glass. Carefully place the cover glass over the drops of water and sediment so that they are suspended between the slide and cover glass (see figure below). You should be able to look at the edge of the drop under oil emersion (100X). Lastly, if you find few or none, save the container you collected the sediment in and check on it periodically (monthly). Sooner or later they should bloom. The jar (mayonase or peanut butter sized) itself should be filled 1/3 sediment, 1/3 water, and loosely capped (see figure below). Good luck.