2023
The growth of bacterial colonies is the result of single-cell scale processes (such as cell division or cell motility [1]) but also larger scale physical processes (emergence of collective motility [2], surface wetting [3]). In the case of the bacteria Pseudomonas aeruginosa (3 μm in length, 0.5 μm in diameter), this yields to the formation of branched colonies at the surface of agar gel (Figure 1). A colony covers a 10-cm diameter Petri dish in 20 hours, while each cell is able to swim at 50 μm /s. The thickness of the colony varies from 0.5 μm (monolayer of cells, Figure 2) to 20 μm. The links between single-cell motility to macroscopic spreading are still poorly understood. Quantitative understanding of the physical mechanisms that control bacterial swarming requires an extensive mapping of the colony, in terms of colony height, spreading speed, cell migration speed and direction, etc.
This internship’s aim is to obtain an unprecedented multiscale atlas of P. aeruginosa swarming colony, by combining innovative microscopy techniques. The first level of study will be a multiscale snapshot description of a late-stage colony. The second level will be a dynamic mapping (including description of biomass flows, via image analysis techniques like PIV and tracking of colony features) of colony formation. If time permits, this description will be reproduced on motility mutants, whose impaired single-cell motility translates into a change of macroscopic behaviour. This internship is a good opportunity to learn various imaging techniques (phase contrast, fluorescence, reflection), automated imaging acquisition (included by custom-made scripts), image analysis.
