Spatio-temporal dynamics within microbial communities

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

 

Adhesin dynamics in single bacteria

We currently aim to elucidate the mechanisms that set the polarity of adhesion at the level of a single cell in E. coli. Therefore, we developed a collaboration with C. Beloin (Institut Pasteur) and A. Gautier (Sorbonne University) to visualize adhesin dynamics in single bacteria (Chekli et al., Sci Rep 2020).  

    

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Morphogenesis of bacterial microcolonies

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). We identified that polar adhesion is a key determinant for microcolony morphogenesis as it influences the shape of the first monolayer and the transition from 2D to 3D growth ( Duvernoy et al., Nat Commun 2018). Thus, the distribution of adhesion molecules on the bacterial outer envelope sets the upper level of organisation at the microcolony scale.

               

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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 (Julou et al., PNAS 2013). 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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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 adaption dynamics 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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eSLAP, a new nich for Listeria in epithelial cells

A number of bacterial pathogens spend a part of their infectious cycle intracellularly; internalisation into host cells can allow them to cross cellular barriers, escape humoral immune surveillance, or disseminate throughout the organism as cargo of circulating cells. After internalisation, bacteria are entrapped inside primary vacuoles from where they can follow two distinct routes: either subverting vacuoles, or leaving them. Listeria is tought to rapidly escape from primary entry vacuoles due to the combined action of the pore-forming toxin, listeriolysin O (LLO, encoded by the hlyA gene), and of two phospholipases (PlcA and PlcB), before being able to replicate in the cytosol. Recently, we showed that in peithelial cells Listeria was able to grow inside entry vacuoles (eSLAP) as efficiently as in the cytosol (Peron-Cane et al., PLoS Pathogens 2020) (collaboration A. Lebreton, M. Lecuit & A. Gautier)

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Yeast in fluctuating environment

In natural habitats microbes experience changing environments, which fluctuate either randomly or cyclicly. In this project, we propose to perform cyclic laboratory perturbations on S. cerevisiae growing in a bioreactor. In the context of fluctuating environments, we propose in collaboration with Jean-Baptiste Boulé to study the adaptive responses to cyclic challenging environments associated with time-structured stimuli.

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Aggregation of algae in response to predation

The transition from unicellular to multicellular organization occurred more than twenty times independently along the tree of life. Multicellularity provides cells with novel opportunities, such as increased resistance to predation and division of labour. However, larger group sizes are also associated to increased competition for resources and environmental toxification. With Raphaël Jeanneret, we aim to tackle this issue with the model system C. Reinhardtii, which aggergates in response to predation.        

        

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