Measurement of the elasticity of the actin tail of Listeria monocytogenes

We report biophysical experiments performed on the bacterium Listeria monoc ytogenes, a model system to study actin-based motility. Using optical tweez ers and electrophoresis experiments, we find that the bacterium is firmly a ttached to its tail, and we demonstrate that the tail responds as an elasti c gel when deformed. We have measured its elastic modulus at a value of 10( 3)- 10(4) 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 tak es into account the connection and thus the interaction between the actin f ilaments. It provides a generic description of the various aspects of actin -tail based movements.