( Scientists at the Naval Research Labora...)Researchers reveal mystery of bacterial magnetism

Scientists at the Naval Research Laboratory (NRL) and Purdue University have shed light on one of microbiology's most fascinating mysteries--why some bacteria are naturally magnetic. Their description of how being magnetic "helps" the bacteria is reported in the August 2006 issue of the Biophysical Journal.

Magnetic bacteria are found in a variety of aquatic environments, such as ponds and lakes. The strain of bacterium the research team studied, Magnetospirillum magneticum, was originally found in a pond in Tokyo, Japan. Magnetic bacteria typically live far below the surface, where oxygen is scarce. (They do not grow well where oxygen is plentiful.) What makes them fascinating is that they naturally grow strings of microscopic magnetic particles called magnetosomes. When placed in a magnetic field, the bacteria align like tiny swimming compass needles, a phenomenon call magnetotaxis.

The research team is using genetic engineering to create a strain of the bacteria that become magnetic only when exposed to specific toxic chemicals, with the goal of using them as living chemical sensors. As a first step, they have created a strain that cannot make magnetosomes and therefore is not magnetic. Dr. Lloyd Whitman from NRL, who led the research team, explains that "during the course of our research, we realized that nobody had ever really demonstrated that being magnetic actually helps the bacteria." "Genetic modification allowed us to directly observe differences in behavior between magnetic and non-magnetic versions of the same bacterium," adds Professor Bruce Applegate. Professor Applegate directed the genetic engineering at Purdue, with the assistance of Professor Lazlo Csonka, Dr. Lynda Perry, and Ms. Kathleen O'Connor.

In the past, scientists had suspected that being magnetic helps a bacterium find the oxygen concentrations it prefers more quickly by swimming only up and down in the earth's magnetic field rather than randomly in
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Source:Naval Research Laboratory

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