title: Pseudomonas protegens Pf-5 causes discoloration and pitting of mushroom caps due to the production of antifungal metabolites.
abstract: Bacteria in the diverse Pseudomonas fluorescens group include rhizosphere inhabitants known for their antifungal metabolite production and biological control of plant disease, such as Pseudomonas protegens Pf-5, and mushroom pathogens, such as Pseudomonas tolaasii. Here, we report that strain Pf-5 causes brown, sunken lesions on peeled caps of the button mushroom (Agaricus bisporus) that resemble brown blotch symptoms caused by P. tolaasii. Strain Pf-5 produces six known antifungal metabolites under the control of the GacS/GacA signal transduction system. A gacA mutant produces none of these metabolites and did not cause lesions on mushroom caps. Mutants deficient in the biosynthesis of the antifungal metabolites 2,4-diacetylphloroglucinol and pyoluteorin caused less-severe symptoms than wild-type Pf-5 on peeled mushroom caps, whereas mutants deficient in the production of lipopeptide orfamide A caused similar symptoms to wild-type Pf-5. Purified pyoluteorin and 2,4-diacetylphloroglucinol mimicked the symptoms caused by Pf-5. Both compounds were isolated from mushroom tissue inoculated with Pf-5, providing direct evidence for their in situ production by the bacterium. Although the lipopeptide tolaasin is responsible for brown blotch of mushroom caused by P. tolaasii, P. protegens Pf-5 caused brown blotch-like symptoms on peeled mushroom caps through a lipopeptide-independent mechanism involving the production of 2,4-diacetylphloroglucinol and pyoluteorin.
authors.forename: Marcella D
authors.initials: MD
authors.lastname: Henkels
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Kidarsa
authors.forename: Brenda T
authors.initials: BT
authors.lastname: Shaffer
authors.forename: Neal C
authors.initials: NC
authors.lastname: Goebel
authors.forename: Peter
authors.initials: P
authors.lastname: Burlinson
authors.forename: Dmitri V
authors.initials: DV
authors.lastname: Mavrodi
authors.forename: Michael A
authors.initials: MA
authors.lastname: Bentley
authors.forename: Lorena I
authors.initials: LI
authors.lastname: Rangel
authors.forename: Edward W
authors.initials: EW
authors.lastname: Davis
authors.forename: Linda S
authors.initials: LS
authors.lastname: Thomashow
authors.forename: T Mark
authors.initials: TM
authors.lastname: Zabriskie
authors.forename: Gail M
authors.initials: GM
authors.lastname: Preston
authors.forename: Joyce E
authors.initials: JE
authors.lastname: Loper
mesh_terms: D000363:Agaricales / Q000187:drug effects*; D000935:Antifungal Agents / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D055666:Lipopeptides / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D009154:Mutation; D011549:Pseudomonas / Q000235:genetics / Q000378:metabolism*
chemical_list: D000935:Antifungal Agents; D001426:Bacterial Proteins; D055666:Lipopeptides