Measurement of the elasticity of the actin tail of Listeria monocytogenes

We report biophysical experiments performed on the bacterium Listeria monocytogenes, a model system to study actin-based motility. Using optical tweezers and electrophoresis experiments, we find that the bacterium is firmly attached to its tail, and we demonstrate that the tail responds as an elastic gel when deformed. We have measured its elastic modulus at a value of 10³-10⁴ Pa, which is 10 times higher than the rigidity of the eukaryotic cytoplasm. These results demonstrate that the bacterium and its tail form a very robust system, consistent with the steadyness of the motion observed in vivo. We propose an elastic model for the propulsion mechanism which takes into account the connection and thus the interaction between the actin filaments. It provides a generic description of the various aspects of actin-tail based movements.