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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGY AND MANAGEMENT OF SOILBORNE DISEASES OF HORTICULTURAL CROPS

Location: Horticultural Crops Research

Title: Development and Testing of Secondary Metabolism Mutants of Pseudomonas fluorescens PF-5

Authors
item Kidarsa, Teresa
item Henkels, Marcella
item Liu, Diane -
item Loper, Joyce

Submitted to: International Plant Growth Promoting Rhizobacteria Workshop
Publication Type: Abstract Only
Publication Acceptance Date: April 15, 2009
Publication Date: May 17, 2009
Citation: Kidarsa, T.A., Henkels, M.D., Liu, D., Loper, J.E. 2009. Development and Testing of Secondary Metabolism Mutants of Pseudomonas fluorescens PF-5. International Plant Growth Promoting Rhizobacteria Workshop. p. 78.

Technical Abstract: Pseudomonas fluorescens Pf-5, a biological control agent of soil-borne plant diseases, produces at least ten secondary metabolites. Several of these metabolites, including hydrogen cyanide, pyrrolnitrin, pyoluteorin and 2,4-diacetylphloroglucinol have well-characterized roles in biological control. Functions of other metabolites, such as the newly characterized rhizoxin analogs and the lipopeptide, orfamide A, also display antagonistic biological activity. We have modified a system developed in P. aeruginosa for the creation of unmarked deletion mutants for use in Pf-5. This has allowed the creation of mutations in each of the known secondary metabolite biosynthetic gene clusters. These mutations have been sequentially introduced into Pf-5 resulting in strains containing multiple numbers and combinations of deletions. Biological assays utilizing these mutants have been developed to identify the relative contribution of identified secondary metabolites to the phenotype expressed by wild type Pf-5. Wild type Pf-5 shows phytotoxic effects on seed germination and root elongation when applied to rice seed. From assays testing a series of mutants applied to rice seed we found major contributing factors of phytotoxicity to include 2,4-diacetylphloroglucinol and rhizoxin analogs. In antagonism tests against Pseudomonas syringae on King’s Medium B containing iron, a novel compound produced from an orphan gene cluster in the Pf-5 genome was found to be inhibitory to the pathogen.

Last Modified: 9/1/2014
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