Pseudomonas protegens Pf-5 favours self-produced siderophore over free-loading in interspecies competition for iron.

Many microorganisms compete for extracellular iron using strain-specific chelators known as siderophores. The ferric-siderophore complex limits local access to iron because import requires a suitable cognate receptor. Interestingly, many species carry receptors that enable 'cross-feeding' on heterologous siderophores made by neighboring organisms, although little is known about how this ubiquitous behaviour is regulated. Here, we investigated the soil bacterium Pseudomonas protegens Pf-5, a strain remarkable for its ability to use dozens of heterologous siderophores. We characterized the expression of six pyoverdine-type (PVD) siderophore receptors in response to their cognate PVD. In general, we found expression is tightly regulated to reflect availability of their cognate PVD. In contrast, Pf-5 continues to secrete its own primary siderophore, PVD , despite the capability and opportunity to cross-feed. We demonstrate that this strategy is beneficial in co-culture with a competing PVD -producer, P. aeruginosa PAO1. Although Pf-5 can cross-feed on PVD , production of PVD is required to maintain a competitive advantage. We attribute this to an antagonistic effect of PVD on the growth of PAO1, presumably through limiting access to iron. Our results demonstrate the benefits of excluding competitors out-weigh the incentives associated with a free-loader lifestyle for Pf-5.