Cooperation, virulence and siderophore production in bacterial parasites

TLDR

Kin selection theory predicts that parasite virulence is negatively correlated with relatedness, because lower relatedness increases competition for host resources, driving faster growth and higher virulence. The study aims to show that a biological feature of bacterial infections can lead to a positive correlation between relatedness and virulence. High relatedness promotes cooperative siderophore production, boosting bacterial growth and virulence, and this principle extends to other cooperative traits such as immune suppression and biofilm formation. They find that higher relatedness is indeed associated with increased virulence.

Abstract

Kin selection theory predicts that the damage to a host resulting from parasite infection (parasite virulence) will be negatively correlated to the relatedness between parasites within the host. This occurs because a lower relatedness leads to greater competition for host resources, which favours rapid growth to achieve greater relative success within the host, and that higher parasite growth rate leads to higher virulence. We show that a biological feature of bacterial infections can lead to the opposite prediction: a positive correlation between relatedness and virulence. This occurs because a high relatedness can favour greater (cooperative) production of molecules that scavenge iron (siderophores), which results in higher growth rates and virulence. More generally, the same underlying idea can predict a positive relationship between relatedness and virulence in any case where parasites can cooperate to increase their growth rate; other examples include immune suppression and the production of biofilms to aid colonization.