Most free-swimming microorganisms swim in helices. Recent mathematical analyses in this laboratory demonstrate that (1) microorganisms that swim in helices rotate their bodies as they move forward, (2) the rotational and translational velocities determine the radius and pitch of the helix, (3) changes in the rotational velocity change the direction of the axis of the helix (the net direction of motion), and (4) a microorganism can orient to a stimulus gradient by changing its rotational velocity. These investigators have developed a working prototype of a device that tracks the motion of microorganisms in three dimensions. The goals of this project are to refine this device and the techniques of data analysis required to track microorganisms accurately and precisely. The motions of spermatozoa and a flagellate will be tracked to test (1) whether they change their rate of rotation when stimulated, and (2) if the resulting change of direction is sufficient to orient the organism to a stimulus gradient. The results of this research may reveal a previously unknown mechanism by which free-swimming microorganisms orient their direction of motion, i.e., by changing their rate of rotation.
