Steps and fluctuations of Listeria monocytogenes during actin-based motility

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Abstract
The actin-based motility of the bacterium, Listeria monocytogenes, is a model system for understanding motile cell functions involving actin polymerization1. Although the biochemical and genetic aspects of Listeria motility have been intensely studied2,3,4,5, biophysical data are sparse6. Here we have used high-resolution laser tracking to follow the trailing ends of Listeria moving in the lamellae of COS7 cells. We found that pauses during motility occur frequently and that episodes of step-like motion often show pauses spaced at about 5.4 nm, which corresponds to the spatial periodicity of F-actin7. We occasionally observed smaller steps (8 and limit alternative models, such as the ‘elastic’ brownian ratchet9 or the ‘molecular’ ratchet4,10.