Using microscopy, microfluidics and image analysis, combined with numerical analysis, we are currently pursuing two lines of research:
Effects of physical interactions. When the density of a population of motile bacteria increases, the physical interactions between them drive the emergence of collective motions, of different natures depending on the type of motility involved. For example, flagellated bacteria produce swirling collective motions, whereas twitching bacteria tend to move in directed and persistent columns. We work on understanding the physics of these collective motilities and how they impact chemotactic motion, and more generally the organization of the population of cells. We are mainly interested in two questions:
- What happens to chemotaxis when cell density increases for the different types of collective motilities?
- How do the physical properties of the cells modify the collective behavior, especially in the case of mixtures of phenotypes?
The cell suspension (10% volume fraction) is observed in a 50 µm high microfluidic channel at 10x magnification. The map of the local velocities (right) is measured by image velocimetry.
SCale bar 50 µm
Effects of noisy signaling pathway. E. coli swims at low density in a succession of straight second-long runs and short reorientations, the tumbles. The duration of the runs has been shown to fluctuate over time scales of tens to hundreds of seconds. The random walk therefore alternates large explorations and short local searches. We have recently shown how this behavior results from specific elements of the architecture of the chemotaxis pathway. This behavior has been theoretically argued to be an optimal exploration strategy of homogeneous environment for any flagellated bacterium and to improve the chemotactic behavior, despite having been so far reported only in E. coli. We therefore are interested in the following questions:
- Is the fluctuating dynamics truly improving the chemotaxis in E. coli?
- Is this type of dynamics universal? How frequent is it among bacteria?