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Collective behaviors of bacteria
Interacting biological cells can exhibit collective behaviors (clustering, migration…) that our knowledge at the scale of the single cell cannot fully explain. Such systems will be illustrated through experiments performed on chemotactic bacteria (Escherichia coli) swimming in liquid medium.
Their behavior is caused by the balance between the chemotaxis of bacteria towards nutrient gradients present in the medium and the emission of attractant molecules by the bacteria themselves.
In particular, when bacteria are concentrated at the extremity of a microchannel, a concentration wave appears and propagates along the channel. We will discuss new results obtained on this system, in particular by confronting closely the details of the trajectories of single bacteria and the characteristics of these accumulations (velocity, exact profile, time evolution) as well as the way they propagate in different geometries.
Another type of experiment consists in imposing dynamically the biochemical environment experienced by bacteria with a microfluidic device. Such system allows to growth bacteria in very stable conditions, up to very large concentrations and to envision competition experiments between these large populations.