Conservation of the 2,4-diacetylphloroglucinol biosynthesis locus among fluorescent Pseudomonas strains from diverse geographic locations

Abstract

The broad-spectrum antibiotic 2,4-diacetylphloroglucinol (PHL) is a major determinant in the biological control of a range of plant pathogens by many fluorescent Pseudomonas spp. A 4.8-kb chromosomal DNA region from Pseudomonas fluorescens Q2-87, carrying PHL biosynthetic genes, was used as a probe to determine if the PHL biosynthetic locus is conserved within PHL-producing Pseudomonas strains of worldwide origin. The phl gene probe hybridized with the genomic DNA of all 45 PHL-producing Pseudomonas strains tested, including well-characterized biocontrol strains from the United States and Europe and strains isolated from diseasesuppressive soils from Switzerland, Washington, Italy, and Ghana. The PHL producers displayed considerable phenotypic and genotypic diversity. Two phenotypically distinct groups were detected. The first produced PHL, pyoluteorin, and hydrogen cyanide and consisted of 13 strains from almost all locations sampled in the United States, Europe, and Africa. The second produced only PHL and HCN and consisted of 32 strains from the U.S. and European soils. Analysis of restriction patterns of genomic DNA obtained after hybridization with the phl gene probe and cluster analysis of restriction patterns of amplified DNA coding for 16S rRNA (ARDRA) and randomly amplified polymorphic DNA (RAPD) markers indicated that the strains that produced both PHL and pyoluteorin were genetically highly similar. In contrast, there was more diversity at the genotypic level in the strains that produced PHL but not pyoluteorin. ARDRA analysis of these strains indicated two clusters which, on the basis of RAPD analysis, split into several subgroups with additional polymorphisms. In general, the occurrence of phenotypically and genotypically similar groups of PHL producers did not correlate with the geographic origin of the isolates, and highly similar strains could be isolated from diverse locations worldwide.

Developmental trajectories of amphibian microbiota: response to bacterial therapy depends on initial community structure

“…Isolates were screened for ability to inhibit Bd growth and capacity to resist A. obstetricans AMP secretions in vitro. We selected P. fluorescens based on: (i) high prevalence; isolated from 12 of 19 adult hosts examined in the survey, (ii) potential to persist across generations and occur in amphibian hosts from Australia and from North and Central America (Woodhams et al, 2007;Lauer et al, 2008;Walke et al, 2011) and (iii) common implementation as a biocontrol in agriculture, due to a highly conserved, 2,4 DAPG antifungal metabolite, (Keel et al, 1996). A second probiotic, F. johnsoniae, was selected because it was commonly isolated from A. obstetricans tadpoles.…”

Molecular analysis of a novel gene cluster encoding an insect toxin in plant‐associated strains of Pseudomonas fluorescens

“…Two representative strains were tested, i.e. P. fluorescens Q2-87, an effective biocontrol agent that produces the toxic exoproducts DAPG and HCN (Keel et al, 1996;Bangera and Thomashow, 1999;Maurhofer et al, 2004), and P. fluorescens P3, a strain that does not produce the biocontrol-relevant toxic exoproducts DAPG, PLT or HCN, and lacks biocontrol activity (Voisard et al, 1989;Maurhofer et al, 1998). Injection of CHA0 or Pf-5 at 3 ¥ 10 4 cells per Galleria larva killed all insects within 24 h whereas about 60% and 95% of the larvae survived exposure to an identical cell concentration of the naturally Fit-deficient strains Q2-87 and P3 respectively ( Fig.…”

“…Pseudomonas fluorescens strains CHA0 and Pf-5, the subjects of this study, are prominent, well-characterized representatives of a genetically distinct subgroup of biocontrol pseudomonads that excrete multiple antimicrobial compounds, notably DAPG, PLT, pyrrolnitrin and HCN (Keel et al, 1996;Haas and Keel, 2003;Loper and Gross, 2007). Strain CHA0 was isolated from the roots of tobacco grown in a naturally disease-suppressive soil in western Switzerland (Stutz et al, 1986).…”

Impact of Pseudomonas fluorescens strain CHA0 and a derivative with improved biocontrol activity on the culturable resident bacterial community on cucumber roots

“…To determine the abundance of dominant genotypes of resident bacteria, the 3300 isolates obtained at the sampling date after 10 days were analyzed with the ARDRA technique as described in detail previously [45]. Brie£y, bacterial cultures were grown for 48 h at 24³C in microtiter plates containing 100 Wl of TSB per well and 0.5 Wl of the cultures was transferred directly to PCR tubes for heat lysis in a total volume of 5 Wl of lysis bu¡er (10 mM Tris-HCl, pH 8.3, 50 mM KCl, 0.1% Tween 20).…”

“…The ¢nal volume of the PCR reactions was 20 Wl. Primers with the following sequences were used to amplify the full length of the 16S rDNA gene: 5P-GCTCA-GATTGAACGCTGGCG (forward) and 5P-CGGT-TACCTTGTTACGACTTCACC (reverse) [45]. Restriction of 10 Wl of the ampli¢ed product was performed in a total volume of 20 Wl of restriction bu¡er with 2 U of either CfoI or TaqI (Boehringer, Mannheim, Germany).…”