Living Magnets

By Dr. Sherwood B. Idso

How do animals navigate? There are many theories as to how they are able to find their way about and move in the proper directions for purposes of migration and food gathering. Some scientists think that animals may observe the orientation of the stars; some suggest that they may be able to detect certain light properties our eyes cannot discern; and some believe animals can hear certain sounds that are of too low frequency for our ears to detect. Other scientists believe that some creatures may have a heightened sense of smell or an ability to remember landmarks. One of the most intriguing theories, however, is that many animals have an internal compass that responds to the magnetic field of the earth.

Although the possibility that animals can detect weak magnetic fields has been studied for years in certain birds, fish, and amphibians, and has been proven to have some validity, it was the humble world of bacteria that produced the first concrete evidence for the existence of actual living magnets.

The story begins with the discovery of magnetotactic bacteria (bacteria that move in the same direction as the magnetic field lines of the earth). While microscopically examining some marine and freshwater muds collected from the area of Woods Hole, Massachusetts, Dr. R. P. Blakemore noticed that various kinds of bacteria that live in the sediments consistently swim to the north when separated from the mud. He also found that he could control their direction of swimming with a small bar magnet.

But what was the mechanism involved in this unusual behavior? Just last year the answer was finally obtained. In studying some of the bacteria under the probing eye of an electron microscope, scientists were able to discern that each magnetotactic bacterium contains a chain of cubic crystals composed of magnetite. This mineral, commonly referred to as lodestone, is the material used by ancient mariners in constructing the earliest known compasses.

Each chain of magnetite crystals contains about 22 particles that are produced out of iron compounds found in the muds inhabited by the bacteria. In constructing these particles, the bacteria have solved an interesting problem in physics, for the particle dimensions are of just the right size for a compass. If they were much smaller, the particles would not be able to maintain their common orientation. And if they were much larger, they would break up into disorganized pieces that would cancel out each other’s magnetic effects.

Since the original discovery of magnetotactic bacteria at Woods Hole, several different species from both fresh water and marine environments have been found, all of which swim toward the north. At the latitudes where these bacteria have been discovered, however, the magnetic field lines of the earth also point downward, as well as north. Scientists thus speculate that one purpose of bacterial compasses is to help their owners locate their favorite mud sediments, since a bacterium in water is too small to tell up from down on the basis of gravity alone. So there is further speculation that if magnetotactic bacteria exist in the southern hemisphere, they may have a reversed polarity and swim in a southerly direction that would also take them down to the mud sediments in that hemisphere. This may well prove to be the case, for Dr. Blakemore and his colleagues have recently subjected north-seeking bacteria to a strong magnectic field oriented opposite to their swimming direction and actually produced south-seeking bacteria.

Much remains to be learned about magnetotactic bacteria. In fact, their discovery seems to have raised as many questions as it has answered. But that is the way science progresses—from question to question—ever probing the unknown and opening up new frontiers for investigation. Surely it is one of the important means provided by our Heavenly Father for revealing to us the magnificent forms and functions of His vast creations.

An electron micrograph of a magnetotactic bacterium. The black squares are part of its magnetic compass. (Photo courtesy of Dr. R. P. Blakemore and Dr. R. B. Frankel.)