Public goods trafficking in bacterial microcolonies

Variability of public goods in clonal population

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. To address this issue, we studied the dynamics of siderophore usage in wild-type clonal micro-colonies of P. aeruginosa growing on solid agar gels. In collaboration with a theoretician (T. Mora @ LPS, ENS), we observed that this dynamics is driven by local exchanges between contacting cells, rather than with the whole colony. These local exchanges were shown to enhance siderophore trafficking within the colony and to impact the fitness of individual cells.

Fig.1: (A) Siderophore fluorescence in a Pseudomonas aeruginosa microcolony. The fluorescence is mostly located in the cell periplasm and varies from cell to cell. (B) The whole microcolony lineage. The color codes for pubic goods concentration.

 

Response to Iron starvation

Under low level of iron, non-producing strains become motile.