The initial step of several human or plant fungal infections requires active penetration of host tissue. For example, active penetration of intestinal epithelia by Candida albicans is critical for dissemination from the gut into the bloodstream. In this project (in collaboration with R. Arkowitz Team in iBV, Institut de Biologie Valrose), we have used PDMS microfabricated array of wells to probe the ability of filamentous C. albicans cells to penetrate and grow invasively in substrates of different stiffness. We show that there is a stiffness threshold for penetration and that invasive growth within a stiff substrate is characterized by dramatic filament buckling, along with a stiffness-dependent decrease in extension rate. Our results show that cell growth and morphology are altered during invasive growth, suggesting stiffness dictates the host cells that C. albicans can penetrate.
In addition to the fabrication and experiments on living matter, we have developed an experiment to probe the mechanical effect of penetration of a rigid object in PDMS. We have looked at it, using two different setups at two different scales (millimetric and tens of micrometers in diameter for the indenter).
albicans
The filament cell (green) and the growth site at the apex (red) are shown during growth in PDMS. Note the buckling of the filament in the centre and the tip of the filament protruding from the PDMS in the lower left.
Bacillus subtilis is a model bacterium to study different biological and physical properties of biofilms. Living mainly in the soil, it preferentially forms biofilms at solid/air or liquid/air interfaces. B. subtilis biofilms at a solid/air interface form macro-colonies and are traditionally studied on agar plates. We develop an experiment to explore biofilm collective motility in contact with external gradients of osmotic pressure. To produce stable osmotic gradients in agar gels, we use a custom-made setup through millifluidics. Biofilms respond to the external gradient by developing an asymmetric shape, consistent with the expectations.
B. subtiles and gradients
Contours of bacterial colony at different times from 12 to 30 hours on an homogeneous medium (up left) and on an osmotic gradient (up right), with the measure of center of mass evolution over time. Bar = 1 cm
Bottom raw: average values of osmolarities for injected solutions (black) and agar (red) in corresponding experiments.
Using microfluidic techniques, we are able to trap one or a few bacteria in microscopic water drops (dispersed in oil) to study properties at the individual or small community level for a large number of samples in parallel.
It is possible to characterize the growth of microorganisms in invert emulsion droplets, by measuring the volume of the droplets over time, this volume depending on osmotic phenomena.
The objective of this experiment is to design a set-up to generate aqueous droplets in a compact stack in an oil phase, to encapsulate bacteria in it in order to study the relationship between population growth and droplet size. The consumption of nutrients during bacterial growth and the production of extracellular matrix polymers have opposite effects on osmotic pressure, and these effects can then be decoupled.
When browsing Université Côte d'Azur website and Université Côte d'Azur components websites by profile ("I am" menu), informations may be saved in a "Cookie" file installed by Université Côte d'Azur on your computer, tablet or mobile phone. This Cookie file contains informations, such as a unique identifier, the name of the portal, and the chosen profile. This Cookie file is read by its transmitter. During its 12-month validity period, it allows to recognize your terminal and to propose the chosen profile as your default home page.
You have accepted the deposit of profile information cookies in your navigator.
You have declined the deposit of profile information cookies in your navigator.
"Do Not Track" is enabled in your browser. No profiles information will be collected.