Novel Cell Motility of Protozoa Living in the Hindgut of Termites

A remarkable symbiotic protozoan in the hindgut of termites was accidentally discovered. Its head and body continuously rotated in opposite directions without stopping or reversing directions. Rotations included the plasma membrane of each part of the cell, and the membrane was continuous across the surface shear zone. This protozoan offers direct visual evidence for the fluid nature of cell membranes, and is the first known example of a rotary motor in eukaryotic cells. The rotary motor is an axostyle that runs through the protozoan like a driveshaft and generates relative torque along its length. The entire plasma membrane of the cell is actually fluid and adheres to the underlying cytoplasm/cytoskeleton, passively following its movements. Cell membranes clearly do not determine the shape or movements of cells. Ectosymbiotic rod bacteria attached to the cell surface are flagellated and propel the protozoan, the first known case of prokaryotic flagella driving locomotion of eukaryotic cells.