Contribution of the Siderophores Pyoverdine and Enantio-Pyochelin to Fitness in Soil of Pseudomonas protegens Pf-5.

Pseudomonas protegens synthesizes two major iron-chelating metabolites (siderophores): pyoverdine (Pvd) and enantio-pyochelin (E-Pch). Although iron sequestration and uptake seem to be the main biological role of these siderophores, other functions including metal homeostasis and antibiotic activity have been proposed. The aim of this study was to evaluate the contribution of Pvd and E-Pch to the survival of P. protegens in soil using wild type and isogenic mutant strains unable to produce Pvd, E-Pch or both siderophores. Survival of these strains in sterile soil microcosms, in soil microcosms containing the native microflora and in sterile soil microcosms containing fusaric acid (a mycotoxin able to chelate iron and other metals), was compared by determination of colony forming units (CFU) per gram dry soil over time. In sterile soil, cell densities of Pvd-producing strains were significantly higher than that of non-producers after 21 days of permanence in the microcosms. In non-sterile soil, viability of all strains declined faster than in sterile soil and Pvd producers showed higher CFU × (g dry weight soil)-1 values than non-producers. The presence of fusaric acid negatively affected viability of strains unable to produce Pvd, while had no effect on the viability of strains able to produce Pvd. Altogether, these results show that the ability to produce Pvd increases survival of P. protegens in soil, while the ability to synthesize E-Pch does not, indicating that under the conditions which prevail in soil, iron scavenging via Pvd is more beneficial than via E-Pch.