Filtering Microbial Populations with a Magnetic Field

Magnetic fields strongly affect currents of electrically charged particles such as electrons, protons and other ions in solution. Because ionic currents of protons or sodium drive the rotation of bacterial flagella, it is possible that the motion of motile bacterial species will be affected if they swim through a strong magnetic field. We tested this prediction in mixed cultures of soil bacteria and observed that a magnetic field does in fact exert a filtering effect that alters the composition of the mixed population of motile species. We then monitored motility and growth to see if magnetic fields affected individual bacterial species (Vibrio, Enterobacter sp. and Pseudomonas sp.) The same magnetic field had no observable effect on motility or growth. Although magnetic fields may have served as a selective factor in the evolution of certain species such as magnetotactic motile bacteria, they do not appear to have a direct effect on the ionic current driving flagellar rotation.