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Appl. Environ. Microbiol., Feb 1996, 552-563, Vol 62, No. 2
C Keel, DM Weller, A Natsch, G Defago, RJ Cook and LS Thomashow
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 disease-suppressive 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.
Copyright © 1996, American Society for Microbiology
Conservation of the 2,4-diacetylphloroglucinol biosynthesis locus among fluorescent Pseudomonas strains from diverse geographic locations
Institute of Plant Sciences/Phytopathology, Swiss Federal Institute of Technology, Zurich, Switzerland.
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