Welcome to the Digital Learning Center for Microbial Ecology

Magnetic Microbes

by Sandi Clement

In nature, organisms use a variety of methods to figure out where they are and where they need to be going. Plants use sunlight and the force of gravity to determine which direction they should grow, birds migrate in part using the sun and stars to guide their path, and we humans can simply ask for directions at the nearest gas station. Some organisms use the earth's geomagnetic field to orient themselves and navigate through their environment. Organisms that use the earth's geomagnetic field have some type of internal compass. The smallest organisms that use this navigational method are called magnetotactic bacteria.

Magnetotactic bacteria were discovered in 1975 by Richard P. Blakemore. Blakemore noticed that some of the bacteria that he observed under a microscope always moved to the same side of the slide. If he held a magnet near the slide, the bacteria would move towards the north end of the magnet. These bacteria are able to do this because they make tiny, iron-containing, magnetic particles. Each of these particles is a magnet with a north pole and a south pole. The bacteria arrange these tiny magnets in a line to make one long magnet. They use this magnet as a compass to align themselves to the earth's geomagnetic field.

Why would these bacteria need a compass? Like many other types of bacteria, magnetotactic bacteria don't like oxygen very much. They will move away from areas with high oxygen and toward areas with low or no oxygen. In an aquatic environment, the level of oxygen decreases as one moves deeper into the water. So, magnetotactic bacteria like to live in the deeper parts of their aquatic environments. They use their magnetic compass to tell them which way is down.

How do they do this? It has to do with the direction of the geomagnetic field. In the Northern Hemisphere; the geomagnetic north actually points down at an angle. So, magnetotactic bacteria that are aligned to this field are also pointing down. By moving north along this field, they move deeper into the water, and into areas with less oxygen. Interestingly, in the Southern Hemisphere, the geomagnetic north actually points up and at an angle. So, magnetotactic bacteria in this half of the world are "south-seeking", which points them downward. At the equator, the geomagnetic north doesn't point up or down, so the magnetotactic bacteria found there are a mixture of north-seeking and south-seeking bacteria.

Scientists are also interested in practical applications involving these magnetic microbes. While it isn't likely we'll be using these bacteria to stick notes to our refrigerators, they could prove to be useful to humans. The tiny magnets that these simple organisms make are far superior to those produced by people. So, scientists and engineers are trying to develop ways to use this magnetic material in places where tiny magnets are much better than big magnets.

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