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United States Department of Agriculture

Agricultural Research Service

Research Project: BIOLOGICALLY-BASED SYSTEMS FOR SOILBORNE DISEASE CONTROL IN TREE FRUIT AGRO-ECOSYSTEMS Title: Extracellular metabolites limit bacterial susceptibility to predation in a protist-specific manner and their regulation may be protist-induced

Authors
item Mazzola, Mark
item Loper, Joyce
item Mavrodi, D -
item Thomashow, Linda
item Kobayashi, D -
item Dekkers, E -
item Raaijmakers, J -

Submitted to: Microbial Ecology International Symposium
Publication Type: Abstract Only
Publication Acceptance Date: May 10, 2010
Publication Date: N/A

Technical Abstract: Bacteria employ various strategies to evade protozoan predation, including production and release of bioactive compounds. This capability may be instrumental in determining bacterial resistance to protozoan grazing, thereby enhancing survival of producing strains in soil environments. A limited number of exometabolites have been examined in this regard, and only few studies have demonstrated the distinct nature of the specific response to an individual metabolite. Studies were conducted to assess the capacity of bacterial metabolites to limit predation by the amoeba-flagellate Naegleria americana and the ciliate Colpoda sp. Protists exhibited differential sensitivity to diverse cyclic lipopeptides (CLPs) produced by Pseudomonas fluorescens strains and to the antibiotic 2,4-diacetylphloroglucinol (DAPG). Strains SBW25 and SS101, producing the CLPs viscosin and massetolide A respectively, were resistant to grazing by N. americana but not Colpoda. However CLP-deficient mutants of these strains were susceptible to grazing by both protists. The CLP ofamide A produced by strain Pf-5 did not specifically impart predation defense as both the CLP-deficient mutant and parental strain resisted protist grazing. A Pf-5 gacA-mutant was susceptible to grazing by the amoeba but not the ciliate. However, with respect to predation DAPG-deficient mutants of strains Pf-5 and Q8r1-96 retained the phenotype of the respective parental strain. Lysobacter enzymogenes exhibited resistance to predation, but a mutant deficient in lytic enzyme production was susceptible to grazing by both protists. At the molecular level, enhanced CLP gene expression in the presence of N. americana was observed but did not require bacteria-protist physical contact. These studies demonstrate that a diversity of bacterial bioactive compounds may limit susceptibility to predation, that this resistance may occur in a protist-specific manner, and that DAPG production does not limit bacterial predation.

Last Modified: 12/21/2014
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