title: The sigma factor sigma s affects antibiotic production and biological control activity of Pseudomonas fluorescens Pf-5.
abstract: Pseudomonas fluorescens Pf-5, a rhizosphere-inhabiting bacterium that suppresses several soilborne pathogens of plants, produces the antibiotics pyrrolnitrin, pyoluteorin, and 2,4-diacetylphloroglucinol. A gene necessary for pyrrolnitrin production by Pf-5 was identified as rpoS, which encodes the stationary-phase sigma factor sigma s. Several pleiotropic effects of an rpoS mutation in Escherichia coli also were observed in an RpoS- mutant of Pf-5. These included sensitivities of stationary-phase cells to stresses imposed by hydrogen peroxide or high salt concentration. A plasmid containing the cloned wild-type rpoS gene restored pyrrolnitrin production and stress tolerance to the RpoS- mutant of Pf-5. The RpoS- mutant overproduced pyoluteorin and 2,4-diacetyl-phloroglucinol, two antibiotics that inhibit growth of the phytopathogenic fungus Pythium ultimum, and was superior to the wild type in suppression of seedling damping-off of cucumber caused by Pythium ultimum. When inoculated onto cucumber seed at high cell densities, the RpoS- mutant did not survive as well as the wild-type strain on surfaces of developing seedlings. Other stationary-phase-specific phenotypes of Pf-5, such as the production of cyanide and extracellular protease(s) were expressed by the RpoS- mutant, suggesting that sigma s is only one of the sigma factors required for the transcription of genes in stationary-phase cells of P. fluorescens. These results indicate that a sigma factor encoded by rpoS influences antibiotic production, biological control activity, and survival of P. fluorescens on plant surfaces.
authors.affiliation: Institut National de la Recherche Agronomique, Centre de Recherches de Rennes, Le Rheu, France.
authors.forename: A
authors.initials: A
authors.lastname: Sarniguet
authors.forename: J
authors.initials: J
authors.lastname: Kraus
authors.forename: M D
authors.initials: MD
authors.lastname: Henkels
authors.forename: A M
authors.initials: AM
authors.lastname: Muehlchen
authors.forename: J E
authors.initials: JE
authors.lastname: Loper
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000096:biosynthesis* / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D018553:Cucumis sativus; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D009994:Osmolar Concentration; D010572:Pest Control, Biological; D010636:Phenols; D010696:Phloroglucinol / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D010957:Plasmids; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D011758:Pyrroles; D011775:Pythium / Q000254:growth & development; D012091:Repetitive Sequences, Nucleic Acid; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D009838:Oligodeoxyribonucleotides; D010636:Phenols; D011758:Pyrroles; D012808:Sigma Factor; C095503:pyoluteorin; C069567:sigma factor KatF protein, Bacteria; C059817:2,4-diacetylphloroglucinol; D006861:Hydrogen Peroxide; D010696:Phloroglucinol