Siderophores drive invasion dynamics in bacterial communities through their dual role as public good versus public bad

Microbial invasions can compromise ecosystem services and spur dysbiosis
and disease in hosts. Nevertheless, the mechanisms determining invasion
outcomes often remain unclear. Here, we examine the role of
iron-scavenging siderophores in driving invasions of Pseudomonas
aeruginosa into resident communities of environmental pseudomonads.
Siderophores can be “public goods” by delivering iron to individuals
possessing matching receptors; but they can also be “public bads” by
withholding iron from competitors lacking these receptors. Accordingly,
siderophores should either promote or impede invasion, depending on their
effects on invader and resident growth. Using supernatant feeding and
invasion assays, we show that invasion success indeed increased when the
invader could use its siderophores to inhibit (public bad) rather than
stimulate (public good) resident growth. Conversely, invasion success
decreased the more the invader was inhibited by the residents’
siderophores. Our findings identify siderophores as a major driver of
invasion dynamics in bacterial communities under iron-limited conditions.