March
2005
, Volume
18
, Number
3
Pages
260
-
272
Authors
Maria
Péchy-Tarr
,
1
Mélanie
Bottiglieri
,
1
Sophie
Mathys
,
1
Kirsten Bang
Lejbølle
,
1
Ursula
Schnider-Keel
,
1
Monika
Maurhofer
,
2
and
Christoph
Keel
1
Affiliations
1Département de Microbiologie Fondamentale, Université de Lausanne, CH-1015 Lausanne, Switzerland; 2Institut für Pflanzenwissenschaften/Phytopathologie, Eidgenössische Technische Hochschule (ETH), CH-8092 Zürich, Switzerland
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RelatedArticle
Accepted 8 November 2004.
Abstract
Pseudomonas fluorescens CHA0 is an effective biocontrol agent of root diseases caused by fungal pathogens. The strain produces the antibiotics 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) that make essential contributions to pathogen suppression. This study focused on the role of the sigma factor RpoN (σ54) in regulation of antibiotic production and biocontrol activity in P. fluorescens. An rpoN in-frame-deletion mutant of CHA0 had a delayed growth, was impaired in the utilization of several carbon and nitrogen sources, and was more sensitive to salt stress. The rpoN mutant was defective for flagella and displayed drastically reduced swimming and swarming motilities. Interestingly, the rpoN mutant showed a severalfold enhanced production of DAPG and expression of the biosynthetic gene phlA compared with the wild type and the mutant complemented with monocopy rpoN+. By contrast, loss of RpoN function resulted in markedly lowered PLT production and plt gene expression, suggesting that RpoN controls the balance of the two antibiotics in strain CHA0. In natural soil microcosms, the rpoN mutant was less effective in protecting cucumber from a root rot caused by Pythium ultimum. Remarkably, the mutant was not significantly impaired in its root colonization capacity, even at early stages of root infection by Pythium spp. Taken together, our results establish RpoN for the first time as a major regulator of biocontrol activity in Pseudomonas fluorescens.
JnArticleKeywords
Additional keyword:
rhizosphere.
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ArticleCopyright
© 2005 The American Phytopathological Society