Recent Advances in Pseudomonas Biocontrol

Fluorescent Pseudomonads have been intensively studied as biocontrol agents. These organisms exhibit an enormous metabolic versatility and especially isolates from the P. fluorescens group produce a remarkable spectrum of secondary metabolites. Multilocus sequence analysis and phylogenomics have revealed the presence of at least five distinct subgroups in the P. fluorescens group with biocontrol isolates previously classified as P. fluorescens interspersed with strains classified in other species. Antibiotics such as phenazines, diacetylphloroglucinol, and hydrogen cyanide are produced by certain taxonomic groups within the genus Pseudomonas and appear to be ancestral. These compounds often have a physiological role for the producing strain, independent from their antibiotic activity. Other secondary metabolites are only found in certain Pseudomonas isolates and are apparently obtained by horizontal gene transfer. The recent boost in genome sequencing has revealed many orphan biosynthetic gene clusters in the genomes of Pseudomonas biocontrol strains. Genome mining has led to the discovery of many new antimicrobial compounds with a role in biocontrol of plant pathogenic fungi, oomycetes and bacteria. Moreover, some Pseudomonas biocontrol strains produce potent insect toxins. The versatility of Pseudomonas biocontrol agents continues to surprise.