Temperature dependence of the motility of the parasitic microswimmer Trypanosoma brucei

The parasitic unicellular microswimmer Trypanosoma brucei is the causative agent for severe diseases in humans and cattle. Trypanosomes have a complex life cycle with the best-characterized stages being the bloodstream form (BSF) in the vascular system of the mammalian host and the procyclic form (PCF) in the gut of the tsetse fly vector. Morphologically, PCF and BSF trypanosomes appear very similar, being propelled by a single flagellum that is wrapped around the spindle-shaped cell body. Despite this similarity, we show here that PCF and BSF trypanosomes have significantly different motility patterns and are also very different in their sensitivity to the ambient temperature. PCF cells show a clear run-and-tumble pattern with an improved motility for increasing temperatures, most likely facilitating long-range transport in the gut of the poikilothermic tsetse fly. These features are even preserved in mutants with compromised post-translational modification of microtubules. In contrast, BSF trypanosomes show a considerably more erratic motility that hardly varies with temperature, potentially indicating that an active exploration of the host's body fluids with a directed motility is not necessary for the parasite's life cycle.