Adverse effects of microgravity on the magnetotactic bacterium Magnetospirillum magnetotacticum

Bacteria that contain magnetosomes display magnetotaxis and align themselves to the earth's magnetic field. When magnetotactic bacteria were first isolated several decades ago it was presumed that geomagnetic orientation allowed magnetotactic bacteria to orient themselves downward towards sediments where the habitat is favorable to their growth and metabolism. As more species of magnetotactic bacteria have been isolated and studied, differences in magnetotactic responses have been observed which suggested that the primary role of magnetosomes might simply be to enhance a microorganism's response to gravity. To resolve if gravity influences magnetotactic behavior in bacteria, Magnetospirillum magnetotacticum was used to examine magnetotaxis in the absence of gravity. Experiments to compare the orientation of bacteria to north- or south-pole magnets were conducted in normal gravity and in the microgravity environments aboard the Space Shuttle and Space Station MIR. In each of the microgravity situations studied, bacteria were impaired in their ability to orient to magnets and the failure to exhibit magnetotaxis appeared to be a function of the loss of magnetosomes. The disappearance of aggregated magnetosomes seemed to correlate with a general loss of cellular integrity in microgravity.