Cheating and resistance to cheating in natural populations of the bacterium Pseudomonas fluorescens

Bacteria perform cooperative behaviours that are exploitable by non-cooperative cheats, and cheats frequently arise and coexist with cooperators in laboratory microcosms. However, evidence of competitive dynamics between cooperators and cheats in nature remains limited. Using the production of pyoverdine, an iron-scavenging molecule, and natural soil populations of Pseudomonas fluorescens, we found that (1) non-producers are present in the population; (2) they co-occur (<1cm3) with pyoverdine producers; (3) they retain functional pyoverdine receptors and (4) they can utilize the pyoverdine of on average 52% of producers. This suggests non-producers can potentially act as social cheats in soil: utilizing the pyoverdine of others while producing little or none themselves. However, we found considerable variation in the extent to which non-producers can exploit cooperators, as some cooperators appear to produce exclusive forms of pyoverdine or kill non-producers with toxins. We examined...