Pseudomonas fluorescens Pf-5 is a plant commensal bacterium that inhabits the rhizosphere and produces secondary metabolites that suppress soilborne plant pathogens. The complete sequence of the 7.1-Mb Pf-5 genome was determined. We analyzed repeat sequences to identify genomic islands that, together with other approaches, suggested P. fluorescens Pf-5's recent lateral acquisitions include six secondary metabolite gene clusters, seven phage regions and a mobile genomic island. We identified various features that contribute to its commensal lifestyle on plants, including broad catabolic and transport capabilities for utilizing plant-derived compounds, the apparent ability to use a diversity of iron siderophores, detoxification systems to protect from oxidative stress, and the lack of a type III secretion system and toxins found in related pathogens. In addition to six known secondary metabolites produced by P. fluorescens Pf-5, three novel secondary metabolite biosynthesis gene clusters were also identified that may contribute to the biocontrol properties of P. fluorescens Pf-5.Pseudomonas spp. are ubiquitous inhabitants of soil, water and plant surfaces that belong to the Gamma subclass of Proteobacteria. Many pseudomonads live in a commensal relationship with plants, utilizing nutrients exuded from plant surfaces and surviving environmental stress by occupying protected sites provided by the plant's architecture. These commensal species can have profound effects on plants by suppressing pests, enhancing access to key nutrients, altering physiological processes or degrading environmental pollutants. Pseudomonads have an exceptional capacity to produce a wide variety of metabolites, including antibiotics that are toxic to plant pathogens 1,2 . Antibiotic production by plant-associated Pseudomonas spp. enhances the fitness of the producing strain 3 and suppresses pathogens that would otherwise jeopardize plant health 1,2,4 . Certain antibiotic-producing strains of Pseudomonas spp. function as biological control agents; their capacity to protect plants from disease distinguishes them as microorganisms with immense effects on agricultural productivity.Among the plant commensals, P. fluorescens Pf-5 is notable as a biological control organism, for its rhizosphere competence and the spectrum of antibiotics and other secondary metabolites that it produces. P. fluorescens Pf-5 inhabits the rhizosphere of many plants and suppresses plant diseases caused by soilborne plant pathogens [5][6][7][8][9][10][11] . P. fluorescens Pf-5 produces a suite of antibiotics including pyrrolnitrin 5 , pyoluteorin 11 and 2,4-diacetylphloroglucinol 12 . It also produces hydrogen cyanide and the siderophores pyochelin and pyoverdine, which can suppress target pathogens in the rhizosphere through iron competition 13,14 . In this study, we report the complete genome sequence of P. fluorescens Pf-5, and highlight genes with a demonstrated or proposed role in biological control or rhizosphere colonization.
RESULTS
Genome features and comparati...