Magnetotactic bacteria contain chains of magnetic iron minerals that allow them to orient in the earth’s magnetic field much like living compass needles. These bacteria have long been observed to respond to high oxygen levels in the lab by swimming towards geomagnetic north in the Northern Hemisphere and geomagnetic south in the Southern Hemisphere. In either hemisphere, this behavior would also lead them downward in the water column into areas with their preferred oxygen level. But an unusual bacterium in New England has been found doing just the opposite, a magnetic misfit of sorts.
Scientists have dubbed the bacterium the barbell for its appearance. In a study reported in this week’s issue of Science, researchers from the Woods Hole Oceanographic Institution (WHOI) and Iowa State University used genetic sequencing and other laboratory techniques to identify the barbell, which was found coexisting with other previously described magnetotactic bacteria in a local marine pond in Falmouth, MA. They also found dense populations of a small, unidentified rod-shaped bacterium that showed a similar "backwards" behavior.
Magnetotactic bacteria concentrate large amounts of iron within their cells, far more than all other marine bacteria. They could play a significant role in iron cycling in stratified marine environments, particularly ponds and salt marshes.
Lead author Sheri Simmons of the Woods Hole Oceanographic Institution says magnetotactic bacteria are found throughout the world in chemically stratified marine and freshwater environments. They can reach high densities under the right conditions and will swim along the magnetic field axis and up or down in the water column to locate their preferred or ideal living conditions. If oxygen levels are too high or too low, they will seek a layer in the water column where the level is just right.
Shelley Dawicki | EurekAlert!
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