Myxococcus motility on agar

How do bacteria move on solid surfaces?
How do they direct their movements?
How does multicellular cooperation emerge from signal integration?
How did multicellularity evolve?

We are using the gram-negative bacterium Myxococcus xanthus as a model system to address these fundamental questions. Specifically, we are using a multidisciplinary approach from the realms of genetics, biochemistry, cell biology, bioinformatics and quantitative physics to study the motility mechanism and its regulation in response to environmental cues, both at the single and multicellular levels. In the longer term, our goal is to build a high-resolution model of a bacterial multicellular life cycle integrating knowledge from experiments and computational simulations. 

Motility model

How does Myxococcus move on surfaces?

We are interested in determining the mechanism of the so-called Myxococcus (A)-motility, a process where the bacterial cell moves smoothly along its long axis in absence of obvious extracellular organelles. Combining genetics, cell biology and physics, we have recently identified the motility machinery for the first time. Work from ours and other laboratories have led to a working model, proposing that ventral assembly of the motility complex promotes movement. However, how the machinery propels the cells is still obscure. How are traction forces produced? Is there a connection with the cytoskeleton? How is the directionality of the system dictated? Are some of the questions that we are trying to address. To do this, we are combining techniques from the realms of genetics, cell biology and physics. For more information, see Mignot et al. (2007), Sun, Wartel et al. (2011), Luciano, Agrebi et al. (2011).

Vidéo YouTube

How do cells direct their motility?

Myxococcus cells can change their direction of movement by a process called a reversal where the poles exchange roles, allowing the bacteria to rapidly move in the opposite direction. Such rapid directional changes result from pole-to-pole switching of a central Ras-like small G-protein, MglA. Genetic control of these switches is at the heart of the Myxococcus multicellular lifestyle, swarming, prdation and fruiting body formation. How is MglA localization controlled dynamically? What signalling pathways control MglA localization? How is MglA regulating motility? How are those regulations affecting cell-cell cooperation in groups? For more information, see Mignot et al. (2005), Mauriello, Mouhamar et al. (2010), Zhang et al. (2010).

How do cells sense their siblings and environment?

Chemoreceptor alignment following cell contact

How do cells sense their siblings and environment?

Multicellular cooperation arises from cell-cell signalling and environment sensing and chemotaxis. The localization of a Myxococcus xanthus cytoplasmic receptor (Methyl-accepting Chemotaxis Protein, MCP) changes dynamically in response to cell contacts. This observation suggests that Myxococcus cells possess a “sense of touch” allowing cells to respond to the external environment by modulating coordinated cell movement. Myxococcus has a total of 21 MCP encoding genes. Some of them have been characterized genetically and biochemically. Similar to enteric bacteria, these receptors might be cross-linked with each other and form complex arrays ultimately generating sensory machineries. We are trying to characterize these sensory machineries and understand the link between the localization of bacterial chemoreceptors in cells and their function during chemotaxis