Interactions mediated by a public good transiently increase cooperativity in growing Pseudomonas putida metapopulations

TL;DR

This study investigates how transient increases in cooperation occur in Pseudomonas putida populations due to public good interactions, specifically pyoverdine, and models how environmental accumulation influences social dynamics.

Contribution

It introduces a model that accounts for the changing benefits of pyoverdine accumulation, revealing transient cooperation increases in bacterial metapopulations.

Findings

Initial global producer fraction increases in metapopulations.

Pyoverdine benefits decline at high concentrations, causing transient cooperation.

Experimental validation confirms model predictions.

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.