Appl. Environ. Microbiol., Mar 1995, 849-854, Vol 61, No. 3
J Kraus and JE Loper
A 21-kb region required for the biosynthesis of the polyketide antibiotic
pyoluteorin by the biological control agent Pseudomonas fluorescens Pf-5
was identified and cloned. Seven previously isolated mutants deficient in
pyoluteorin production (Plt(sup-)) had Tn5 insertions spanning the 21-kb
region. Sequences flanking Tn5 inserts were cloned from genomic DNA of
three Plt(sup-) mutants and used as probes to identify wild-type alleles of
the plt loci from a genomic library of Pf-5. Five cosmids containing
overlapping regions of genomic DNA hybridized to one or more of the probes.
One cosmid, pJEL1938, contained the entire 21-kb region and, when
introduced into a Plt(sup-) mutant, partially restored pyoluteorin
production. To study the expression of the genes required for pyoluteorin
biosynthesis, the transposon Tn3-nice, which contains a promoterless ice
nucleation gene (inaZ) and a type I neomycin phosphotransferase gene, was
introduced into the genomic plt region of Pf-5. Carbon sources that
influenced pyoluteorin production by Pf-5 had parallel effects on ice
nucleation activity of Pf-5 containing a genomic plt::Tn3-nice fusion,
indicating that inaZ was transcribed from a promoter of the plt region.
Cells of Pf-5 containing a genomic plt::Tn3-nice fusion expressed ice
nucleation activity on cotton and cucumber seeds planted in field soil. The
expression of plt genes by Pf-5 in the cucumber spermosphere was delayed in
comparison with expression in the cotton spermosphere. This study
demonstrates that genes required for pyoluteorin production were expressed
in situ by the biological control bacterium.
Copyright © 1995, American Society for Microbiology
Characterization of a Genomic Region Required for Production of the Antibiotic Pyoluteorin by the Biological Control Agent Pseudomonas fluorescens Pf-5
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331, and Horticultural Crops Research Laboratory, USDA Agricultural Research Service, Corvallis, Oregon 97330
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