The Physics of Listeria Propulsion

Abstract

Listeria is a pathogenic bacterium, which can be dangerous for immune deficient individuals. It can be found almost everywhere, in particular in food such as soft cheese and smoked salmon. After ingestion, it is able to penetrate in the cellular system where it moves from cell to cell and divides on average every twenty minutes. The reason why it can move from cell to cell is that it develops a comet-like tail (Fig. 1), which pushes the bacterium forward and deforms the plasma membrane until it invades the neighbouring cell. Since it is inside the cellular system it is hard to be detected by the immune system. In order to understand the Listeria propulsion mechanism, a particularly intense scientific activity has been developed over these last years [1,2]. Why should one be particularly interested in this problem? The reason is that Listeria motility is due to the polymerisation and cross-linking of an actin gel (i.e. the comet) just like eukaryotic cell motility is due to the polymerisation of actin in the cell lamellipodium. It is then believed that learning something on Listeria is useful for understanding eukaryotic cells as well. Of course studying Listeria does not avoid studying eukaryotic cells since there are many more aspects to eukaryotic motility than to Listeria motility [3] (like adhesion, molecular motors etc.). Yet this allows us to select one aspect, namely actin polymerisation and cross-linking, in geometrical conditions, which are much simpler than those of eukaryotic cells since the process is exterior to the bacterium.