Title: Interactions mediated by a public good transiently increase cooperativity in growing Pseudomonas putida metapopulations,
Abstract: Bacterial communities have rich social lives. A well-established interaction
involves the exchange of a public good in Pseudomonas populations, where the
iron-scavenging compound pyoverdine, synthesized by some cells, is shared with
the rest. Pyoverdine thus mediates interactions between producers and
non-producers and can constitute a public good. This interaction is often used
to test game theoretical predictions on the "social dilemma" of producers. Such
an approach, however, underestimates the impact of specific properties of the
public good, for example consequences of its accumulation in the environment.
Here, we experimentally quantify costs and benefits of pyoverdine production in
a specific environment, and build a model of population dynamics that
explicitly accounts for the changing significance of accumulating pyoverdine as
chemical mediator of social interactions. The model predicts that, in an
ensemble of growing populations (metapopulation) with different initial
producer fractions (and consequently pyoverdine contents), the global producer
fraction initially increases. Because the benefit of pyoverdine declines at
saturating concentrations, the increase need only be transient. Confirmed by
experiments on metapopulations, our results show how a changing benefit of a
public good can shape social interactions in a bacterial population.