Description du sujet de thèse

Mechanosensing in Myxococcus xanthus: Integration of Mechanical Signals by A- and S-Motility Systems in Collective Behaviors

Contexte de travail

Mechanosensing refers to a cell's ability to detect mechanical variations in its environment (stiffness, topography, shear) and to adapt its motile responses accordingly. While well characterized in eukaryotic cells, this phenomenon remains largely unexplored in bacteria and may be crucial for optimizing migration, predation, and coordinated group behavior.
Myxococcus xanthus, a soil-predatory bacterium, inhabits a naturally heterogeneous mechanical landscape—variations in stiffness, microtopography, and shear stress—that pose constant physical challenges. To navigate and survive in such environments, M. xanthus employs two complementary motility systems: A-motility, which drives individual gliding via focal-adhesion complexes, and S-motility, which powers coordinated group movement via type IV pili. This dual motility is essential for hunting prey, forming biofilms, and adapting to changing environmental conditions.
Recently, our team developed an automated multi-scale imaging platform capable of tracking both single-cell and collective behaviors at high spatiotemporal resolution. Using this approach, we demonstrated that, contrary to the previously assumed mutually exclusive activation, the A and S systems can be co-deployed within the same cell. Moreover, the synergy between these two motors is modulated by the chemical properties of the environment, thereby optimizing both speed and directionality of movement in context-dependent ways. Their joint deployment suggests roles not only in locomotion but also in mechanical adaptation to the surrounding matrix.

Research Question and Objectives
This thesis will investigate whether M. xanthus truly uses its A and S motility systems as mechanical sensors—and, if so, how. Specifically, the project will:
1. Establish polyacrylamide substrates of variable stiffness and quantify the resulting motile responses.
2. Identify the molecular players responsible for mechanical signal detection and integration.
3. Develop a unified model describing how these mechanical stimuli shape both individual and collective motility coordination.

Contraintes et risques

The work will be conducted under BSL-1 conditions using non-pathogenic M. xanthus strains, with strict adherence to microbiological protocols. Preparation and disposal of polyacrylamide gels will follow standard chemical safety practices. Operation of advanced imaging systems requires laser-safety training and routine maintenance procedures. Data archiving and sharing will comply with the laboratory's Open Science policy.

This PhD project offers multidisciplinary training at the intersection of cell biology, materials physics, and quantitative analysis, addressing fundamental questions in bacterial mechanosensing and collective motility.