title: A GacS deficiency does not affect Pseudomonas chlororaphis PA23 fitness when growing on canola, in aged batch culture or as a biofilm.
abstract: Pseudomonas chlororaphis PA23 is a biocontrol agent that protects against the fungal pathogen Sclerotinia sclerotiorum. Employing transposon mutagenesis, we isolated a gacS mutant that no longer exhibited antifungal activity. Pseudomonas chlororaphis PA23 was previously reported to produce the nonvolatile antibiotics phenazine 1-carboxylic acid and 2-hydroxyphenazine. We report here that PA23 produces additional compounds, including protease, lipase, hydrogen cyanide, and siderophores, that may contribute to its biocontrol ability. In the gacS mutant background, generation of these products was markedly reduced or delayed with the exception of siderophores, which were elevated. Not surprisingly, this mutant was unable to protect canola from disease incited by S. sclerotiorum. The gacS mutant was able to sustain itself in the canola phyllosphere, therefore, the loss of biocontrol activity can be attributed to a reduced production of antifungal compounds and not a declining population size. Competition assays between the mutant and wild type revealed equivalent fitness in aged batch culture; consequently, the gacS mutation did not impart a growth advantage in the stationary phase phenotype. Under minimal nutrient conditions, the gacS-deficient strain produced a tenfold less biofilm than the wild type. However, no difference was observed in the ability of the mutant biofilm to protect cells from lethal antibiotic challenge.
authors.affiliation: Department of Microbiology, University of Manitoba, Winnipeg, Canada.
authors.forename: N
authors.initials: N
authors.lastname: Poritsanos
authors.forename: C
authors.initials: C
authors.lastname: Selin
authors.forename: W G D
authors.initials: WG
authors.lastname: Fernando
authors.forename: S
authors.initials: S
authors.lastname: Nakkeeran
authors.forename: T R
authors.initials: TR
authors.lastname: de Kievit
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001203:Ascomycota / Q000254:growth & development; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005816:Genetic Complementation Test; D008049:Lipase / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009154:Mutation; D010447:Peptide Hydrolases / Q000378:metabolism; D010619:Phenazines / Q000378:metabolism; D010944:Plants / Q000382:microbiology; D011549:Pseudomonas / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D011551:Pseudomonas fluorescens / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D017422:Sequence Analysis, DNA; D017262:Siderophores / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D010619:Phenazines; D017262:Siderophores; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria; C074165:lemA protein, bacterial; D008049:Lipase; D010447:Peptide Hydrolases