Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 6/8/2007
Publication Date: 8/26/2007
Citation: Loper, J.E., Bruck, D.J., Pechy-Tarr, M., Maurhofer, M., Keel, C., Gross, H. Genomics of Secondary Metabolite Production by Pseudomonas fluorescens Pf-5. American Society for Microbiology Conference on Pseudomonas. p 23. Interpretive Summary:
Technical Abstract: Pseudomonas spp. are prolific producers of secondary metabolites, and the availability of genomic sequences now opens the door for discovery of novel natural products with potential roles in the ecology and plant growth promoting properties of these bacteria. The rhizosphere bacterium Pseudomonas fluorescens Pf-5 is known to produce six secondary metabolites: the antibiotics pyoluteorin, pyrrolnitrin, and 2,4-diacetylphloroglucinol; two siderophores (a pyoverdine of unknown structure and pyochelin or a related compound), and hydrogen cyanide. The genomic sequence of Pf-5 revealed the presence of three orphan gene clusters, which encode for the biosynthesis of unknown natural products but contain conserved sequences of genes encoding for non-ribosomal peptide synthases or polyketide synthetases. Natural products synthesized from two of these orphan gene clusters have since been identified. Orfamide A, a novel cyclic lipopeptide produced by Pf-5, contributes to swarming motility of Pf-5 and has the capacity to lyse zoospores produced by phytopathogenic Phytophthora spp. (Gross et al. 2007). Several analogs of rhizoxin, a macrocyclic lactone with antifungal activity, are synthesized from a large biosynthetic gene cluster in the Pf-5 genome. Linked to the rhizoxin biosynthetic locus is a cluster of genes encoding for an insect toxin related to Mcf (for “makes caterpillars floppy”) produced by Photorhabdus luminescens, an inhabitant of the gut of entomopathogenic nematodes in the genus Heterorhabditis. If injected into the hemocoel, Pf-5 kills caterpillars of tobacco hornworms (Manduca sexta) whereas an mcf mutant of Pf-5 is less virulent. An oligonucleotide array representing each ORF in the Pf-5 genome has been developed, and is being utilized to explore the influence of the global regulatory genes rpoS and ptsP on transcription of secondary metabolite biosynthesis and efflux genes. The genomic sequence of P. fluorescens Pf-5 provides a variety of insights into this organism’s lifestyle in association with plants and other organisms in the environment.