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Applied and Environmental Microbiology, June 2008, p. 3644-3651, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.00429-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Increased Fitness of Pseudomonas fluorescens Pf0-1 Leucine Auxotrophs in Soil

Wook Kim and Stuart B. Levy^*

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

Received 15 February 2008/ Accepted 9 April 2008

The annotation process of a newly sequenced bacterial genome is largely based on algorithms derived from databases of previously defined RNA and protein-encoding gene structures. This process generally excludes the possibility that the two strands of a given stretch of DNA can each harbor a gene in an overlapping manner. While the presence of such structures in eukaryotic genomes is considered to be relatively common, their counterparts in prokaryotic genomes are just beginning to be recognized. Application of an in vivo expression technology has previously identified 22 discrete genetic loci in Pseudomonas fluorescens Pf0-1 that were specifically activated in the soil environment, of which 10 were present in an antisense orientation relative to previously annotated genes. This observation led to the hypothesis that the physiological role of overlapping genetic structures may be relevant to growth conditions outside artificial laboratory media. Here, we examined the role of one of the overlapping gene pairs, iiv19 and leuA2, in soil. Although iiv19 was previously demonstrated to be preferentially activated in the soil environment, its absence did not alter the ability of P. fluorescens to colonize or survive in soil. Surprisingly, the absence of the leuA2 gene conferred a fitness advantage in the soil environment when leucine was supplied exogenously. This effect was determined to be independent of the iiv19 gene, and further analyses revealed that amino acid antagonism was the underlying mechanism behind the observed fitness advantage of the bacterium in soil. Our findings provide a potential mechanism for the frequent occurrence of auxotrophic mutants of Pseudomonas spp. in the lungs of cystic fibrosis patients.

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* Corresponding author. Mailing address: Center for Adaptation Genetics and Drug Resistance, Department of Molecular Biology and Microbiology, 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

Published ahead of print on 25 April 2008.

Present address: FAS Center for Systems Biology, Harvard University, Cambridge, MA.

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Applied and Environmental Microbiology, June 2008, p. 3644-3651, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.00429-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Silby, M. W., Nicoll, J. S., Levy, S. B. (2009). Requirement of Polyphosphate by Pseudomonas fluorescens Pf0-1 for Competitive Fitness and Heat Tolerance in Laboratory Media and Sterile Soil. Appl. Environ. Microbiol. 75: 3872-3881 [Abstract] [Full Text]