Distribution of Iron Importers and Ecological Traits in Pseudomonas Species Highlights the Potential Role of Efe System in Plant-Related Environments

Iron is essential for bacterial survival; however, the relationship of Pseudomonas species between iron import systems and environmental adaptation remains poorly understood. Multi-locus sequence and pan-genome analyses using 320 Pseudomonas genomes classified the species into four groups: P. aeruginosa, P. putida, P. syringae, and P. fluorescens, each exhibiting distinct patterns of iron importer and siderophore synthetic gene cluster. The P. aeruginosa group contained fewer iron importers, whereas the P. putida group exhibited a higher prevalence of xenosiderophore importers. The Fe²⁺-importing Efe system was predominantly detected in the P. syringae and P. fluorescens groups, both of which include plant pathogens and plant growth-promoting rhizobacteria. Reanalysis of publicly available transcriptome data revealed efeU, foxA, and fpvA were significantly upregulated in plant roots but not in insect hosts, and these genes were specifically suppressed during plant immune responses. Growth test and in planta competitive assay using P. fluorescens wild-type and Efe system-deficient mutant suggested that the Efe system gives an advantage under plant-related environments. Phylogenetic analysis indicated the Pseudomonas Efe system was inherited through vertical gene transfer from a common ancestor. Our comprehensive analysis revealed the distribution of iron importers across Pseudomonas groups, highlighting the importance of these systems in environmental adaptation.