Siderophores and Ferric-Siderophore Receptors of Plant Crowth-Promoting Fluorescent Pseudomonads

Abstract

Plant growth promotion after treatments with selected strains of fluorescent pseudomonads has been reported for different crops and in different cropping systems. For Pseudomonas putida WCS358 it was demonstrated that increased potato root growth and tuber yields in soil from fields cropped in high frequency to potatoes were due to the production of siderophores by this strain, using Tn5-insertion mutants defective in pseudobactin biosynthesis (Bakker et al., 1990). Suppression of Fusarium wilt of carnation by WCS358 has also been observed; again, mutants defective in siderophore biosynthesis are less effective than the wild type (Duijff and Schippers, unpublished). Lemanceau and Alabouvette (1991) describe a synergistic effect of nonpatho?genic Fusarium spp. and certain strains of fluorescent pseudomonas in the biological control of Fusarium wilt. In combination with the nonpathogenic Fusarium oxysporum strain Fo47, P. putida WCS358 resulted in significantly less Fusarium wilt in carnation, compared to the treatment with Fo47 alone, whereas a mutant of WCS358 defective in siderophore biosynthesis did not enhance biological control by Fo47 (Lemanceau and Bakker, unpublished). These results indicate that P. putida strain WCS358 is especially interesting for biological control with regard to its siderophore biosynthesis. Compe?tition for ferric iron mediated by siderophores, to a large extent depends on the specificity of the siderophores and their receptors. In this study the iron uptake via ferric pseudobactins in strain WCS358 is described. Possibilities to make use of the specificities both for fundamental studies and commercial applications are discussed.