Spatial dynamics within microbial communities

Microbes form complex communities that organize in space and time. In the lab we try to understand how physical constraints can influence the structure of the group.

Dynamics of public goods in bacterial populations

The maintenance of cooperation in populations where public goods are equally accessible to all, but inflict a fitness cost on individual producers, is a long-standing puzzle of evolutionary biology. An example of such a scenario is the secretion of siderophores by bacteria into their environment  in order to fetch soluble iron. In liquid cultures, as siderophores diffuse homogeneously, their secretion by a few bacteria benefit the whole colony, resulting in an unstable situation where non-producers are likely to invade the population. On the contrary, on solid surface the structure of bacterial communities can bias the diffucion of public goods. In the lab, we address this issue by monitoring the spatial dynamics of siderophores in P. aeruginosa micro-colonies under the microscope.


               

 

In collaboration with a theoretician (T. Mora @ LPS, ENS), we showed that siderophores are locally exchanged between contacting cells, rather than diffusing freely within the whole microcolony (Movie). This local dynamics enhances the fitness of cells that are directly in contact with producer cells. (collaboration with I. Schalk).

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Morphogenesis of bacterial microcolonies

Surfaces are privileged area where bacteria can attach for initiating the basement of biofilm formation. In this process, the development of a micro-colony from an adherent cell is a key step before the establishement of surface-attached communities.

Since rod-shaped bacteria elongate along their main axis, we would expect the symmetry of the colony to reflect the symmetry of its elementary components. However on solid substrates rod-like bacteria form round microcolonies. To understand how adhesion influences the morphogenesis of microcolonies we perform Laser Ablation and Traction Force Microscopy. (collaboration with M. Balland, S. Lecuyer & C. Beloin)

 

          

 

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Dissemination of viruelnce factors secreted by Listeria within human cells

Bacterial infections are mediated by the secretion of virulence factors that either remain attached to the bacterial envelope or are released in the environment. The understanding of the spatio-temporal distribution of these secretion is still limited by the lack of fluorescent probes that could be functionally exported through bacterial secretion systems. In the lab, we use a new small exportable fluorescent tag (Y-FAST), which reversibly binds a fluorogen, for visualizing the spatial dynamics of virulence factors secreted by L. monocytogenes. (collaboration A. Lebreton & A. Gautier)

 

             

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Evolving along a temperature gradient

Depending on their amplitude, environmental changes either temporal or spatial may stimulate evolution. To investigate how spatial structures influence the speed of adpatation, the lab has designed a continuous chemostat with a temperature gradient in order to measure the adaptive speed along the gradient. The bacteria are fed at a high temperature (60°C) and washed at a low temperature (30°C), thus creating an evolutionary pressure favouring invasion of the high temperature niches.

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