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Applied and Environmental Microbiology, November 2009, p. 6804-6811, Vol. 75, No. 21
0099-2240/09/$08.00+0     doi:10.1128/AEM.01272-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Protozoan-Induced Regulation of Cyclic Lipopeptide Biosynthesis Is an Effective Predation Defense Mechanism for Pseudomonas fluorescens{triangledown}

Mark Mazzola,1* Irene de Bruijn,2 Michael F. Cohen,3 and Jos M. Raaijmakers2

USDA-ARS, 1104 N. Western Ave., Wenatchee, Washington 98801,1 Laboratory of Phytopathology, Wageningen University, Wageningen, The Netherlands,2 Department of Biology, Sonoma State University, 1801 E. Cotati Ave., Rohnert Park, California 949283

Received 2 June 2009/ Accepted 24 August 2009

Environmental bacteria are exposed to a myriad of biotic interactions that influence their function and survival. The grazing activity of protozoan predators significantly impacts the dynamics, diversification, and evolution of bacterial communities in soil ecosystems. To evade protozoan predation, bacteria employ various defense strategies. Soil-dwelling Pseudomonas fluorescens strains SS101 and SBW25 produce the cyclic lipopeptide surfactants (CLPs) massetolide and viscosin, respectively, in a quorum-sensing-independent manner. In this study, CLP production was shown to protect these bacteria from protozoan predation as, compared to CLP-deficient mutants, strains SS101 and SBW25 exhibited resistance to grazing by Naegleria americana in vitro and superior persistence in soil in the presence of this bacterial predator. In the wheat rhizosphere, CLP-producing strains had a direct deleterious impact on the survival of N. americana. In vitro assays further showed that N. americana was three times more sensitive to viscosin than to massetolide and that exposure of strain SS101 or SBW25 to this protozoan resulted in upregulation of CLP biosynthesis genes. Enhanced expression of the massABC and viscABC genes did not require physical contact between the two organisms as gene expression levels were up to threefold higher in bacterial cells harvested 1 cm from feeding protozoans than in cells collected 4 cm from feeding protozoans. These findings document a new natural function of CLPs and highlight that bacterium-protozoan interactions can result in activation of an antipredator response in prey populations.

* Corresponding author. Mailing address: USDA-ARS, 1104 N. Western Ave., Wenatchee, WA 98801. Phone: (509) 664-2280, ext. 207. Fax: (509) 664-2287. E-mail: mark.mazzola{at}ars.usda.gov

{triangledown} Published ahead of print on 28 August 2009.

Applied and Environmental Microbiology, November 2009, p. 6804-6811, Vol. 75, No. 21
0099-2240/09/$08.00+0     doi:10.1128/AEM.01272-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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