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Scientific award

Esther Leburgue - 2/04/2014

Vincent Calvez: A Mathematician Fascinated by Biology

Vincent Calvez Photo credit : Pierre Blondeau - © Inria

Vincent Calvez is a member of Inria’s NuMed team and a specialist in mathematical modelling, so he is at the crossroads of mathematics and the life sciences. His investigations have cast new light on the behaviour of bacteria and have won him a CNRS Bronze Medal, recognising the quality of a researcher’s first work.

What does the CNRS Bronze Medal you have just received represent? 

To begin with, it came as a surprise. You can’t apply for a chance at receiving it. Secondly, it’s a sign of recognition that spotlights the interaction between mathematics and the life sciences. Though many researchers have been studying this area for quite some time, major interest in this subject is fairly recent. So I see this as an encouragement to move forward in this direction.
Can you describe your professional path?  

I specialised in biological applications of mathematics. To do so, I pursued interdisciplinary studies. While a student at ENS Paris, I had the opportunity to complete a semester of biology coursework. For six months, I was an intern at Oxford’s Centre for Mathematical Biology. The ENS Lyon–CNRS pure and applied mathematics unit has hosted my research ever since I finished my thesis. I also belong to the Inria NuMed project team, which operates out of the same lab.

What does your work consist of?

The research with which I am most associated focuses on modelling the collective movement of bacteria. It is the product of my collaboration with the staff—especially Jonathan Saragosti—of the Institut de Curie physical chemistry lab that Pascal Silberzan directs. Jonathan analysed the movement ofE. colicolonies through silicone microchannels as a function of nutrient concentrations in their environment. This is a topic of fundamental biology first studied in the 1960s, but current technology lets us come very close to observing the behaviour of an individual bacterium. As Jonathan continued to conduct experiments, I developed a mathematical model sounder than the one put forward in the 1970s. It allows us to express the movements of both the colony as a whole and its individual members. We now have a better understanding of how bacteria adapt to their environment by migrating towards areas with a greater concentration of glucose, their food. They move as a propagating wave. The bacteria stay together and communicate with each other using an amino acid as a chemical signal.  

What are your next challenges?

I would like to learn more about mathematical wave-propagation models. Such a model could, for example, show how an invasive species of toads in Australia spreads. As with bacterial colonies, the toad population is heterogeneous. But the morphology and endurance of individual toads vary. To better understand the population’s movement, I’d like to be able to calculate the speed of the wave and the degree of diversity within the wave front.

The top image captures successive stages in the wavelike movement of the bacterial colony. The bottom image depicts the trajectories of bacteria within the wave. | J. Saragosti, Institut Curie, Paris | © by Inria

Drawing inspiration from physics to build biological models   

Physics provided Calvez with insight when creating the mathematical model to express the movement of bacterial colonies. He specifically turned to Boltzmann’s model, from the kinetic theory of gases. ‘A gas is a bit like a giant game of pool’, he explains. ‘There is an enormous amount of collisions between molecules. And every collision between two molecules alters their speed and direction’. Though, strictly speaking, bacteria do not collide with each other, they do regularly change direction. ‘These changes in direction are the focus of the model’, says Calvez. ‘We need to know when, how, with which chemical signals, and at what frequencies they occur’. In his model, Calvez adapted physical theory by replacing the collisions of molecules in a gas with the changing directions of bacteria in a colony. 

Keywords: Mathematics Modelling Bacteria Biology Science award