Résumé
While predators and parasites are known for their effects on bacterial
population biology, their impact on the dynamics of bacterial social
evolution remains largely unclear. Siderophores are iron-chelating
molecules that are key to the survival of certain bacterial species in
iron-limited environments, but their production can be subject to cheating
by non-producing phenotypes. In a selection experiment conducted over c 20
bacterial generations and involving 140 populations of the pathogenic
bacterium Pseudomonas aeruginosa PAO1, we assessed the impact of a lytic
phage on competition between siderophore producers and non-producers. We
show that the presence of lytic phages favours the non-producing genotype
in competition, regardless of whether iron use relies on siderophores.
Interestingly, phage pressure resulted in higher siderophore production,
which constitutes a cost to the producers and may explain why they were
outcompeted by non-producers. At the end of the experiment, however,
cheating load reduced the fitness of mixed populations relative to
producer monocultures, and only monocultures of producers managed to grow
in the presence of phage in situations where siderophores were necessary
to access iron. These results suggest that public goods production may be
modulated in the presence of natural enemies with consequences for the
evolution of social strategies.