Speaker
Prof.
Thierry Mora
(ENS)
Description
The maintenance of cooperation in populations where public
goods are equally accessible to all, but inflict a fitness
cost on its sole 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 a well-mixed culture,
these molecules diffuse rapidly, such that all bacteria
experience the same concentration, giving an advantage to
potential cheaters—bacteria that do not produce the public
good but benefit from it. However, on solid substrates,
bacteria form dense and packed colonies, which may alter the
diffusion dynamics through cell-cell contact interactions.
Based on fluorescence microscopy data tracking the
concentration of pyoverdine in P. aeruginosa microcolonies,
we propose a model of local exchange of the public good
between neighboring cells. The model is equivalent to a
model of diffusion on the network of adjacent cells. The
model quantitatively explains the formation of a
concentration gradient, and reproduces the observed
variability of concentration in the population, as well as
its spatial and temporal correlation functions, with only
two parameters. In addition, we show that this local
trafficking modulates the growth rate of individual cells.
Using computer simulations of population dynamics, we show
that this modulation suffices to maintain cooperation
against the invasion of cheaters. Our results give a
physical basis that explains the stability of public goods
production in packed colonies.
Primary author
Prof.
Thierry Mora
(ENS)
