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Applied and Environmental Microbiology, June 2009, p. 3872-3881, Vol. 75, No. 12
0099-2240/09/$08.00+0     doi:10.1128/AEM.00017-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Requirement of Polyphosphate by Pseudomonas fluorescens Pf0-1 for Competitive Fitness and Heat Tolerance in Laboratory Media and Sterile Soil{triangledown}

Mark W. Silby, Julie S. Nicoll, and Stuart B. Levy*

Center for Adaptation Genetics and Drug Resistance and Department of Molecular Biology and Microbiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, Massachusetts 02111

Received 5 January 2009/ Accepted 17 April 2009

Knowledge of the genetic basis for bacterial survival and persistence in soil is a critical component in the development of successful biological control strategies and for understanding the ecological success of bacteria. We found a locus specifying polyphosphate kinase (ppk) and a nonpredicted antisense RNA (iiv8) in Pseudomonas fluorescens Pf0-1 to be necessary for optimal competitive fitness in LB broth culture and sterile loam soil. Pf0-1 lacking ppk and iiv8 was more than 10-fold less competitive against wild-type Pf0-1 in sterile loam soil low in inorganic phosphate. Studies indicated that ppk, and not iiv8, was required for competitive fitness. No role for iiv8 was identified. While a ppk and iiv8 mutant of Pf0-1 did not have increased sensitivity to osmotic, oxidative, and acid stress, it was more sensitive to elevated temperatures in laboratory medium and during growth in sterile soil. ppk was shown to be part of the Pho regulon in P. fluorescens, being upregulated in response to a low external Pi concentration. Of importance, overproduction of polyphosphate in the soil environment appears to be more deleterious than production of none at all. Our findings reveal a new role for polyphosphate (and the need for proper regulation of its production) in competitive fitness of P. fluorescens in laboratory and soil environments.

* Corresponding author. Mailing address: Center for Adaptation Genetics and Drug Resistance, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6764. Fax: (617) 636-0458. E-mail: Stuart.Levy{at}tufts.edu

{triangledown} Published ahead of print on 24 April 2009.

Applied and Environmental Microbiology, June 2009, p. 3872-3881, Vol. 75, No. 12
0099-2240/09/$08.00+0     doi:10.1128/AEM.00017-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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