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Applied and Environmental Microbiology, September 2008, p. 5784-5791, Vol. 74, No. 18
0099-2240/08/$08.00+0     doi:10.1128/AEM.00860-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Global Gene Expression Profiles Suggest an Important Role for Nutrient Acquisition in Early Pathogenesis in a Plant Model of Pseudomonas aeruginosa Infection{triangledown} ,{dagger}

Tiffany L. Weir,1,2 Valerie J. Stull,2 Dayakar Badri,2,3 Lily A. Trunck,4 Herbert P. Schweizer,1,4 and Jorge Vivanco1,2,3*

Program in Cell and Molecular Biology,1 Center for Rhizosphere Biology,2 Department of Horticulture and Landscape Architecture,3 Department of Microbiology, Immunology, and Pathology, Colorado State University, Fort Collins, Colorado 805234

Received 15 April 2008/ Accepted 19 June 2008

Although Pseudomonas aeruginosa is an opportunistic pathogen that does not often naturally infect alternate hosts, such as plants, the plant-P. aeruginosa model has become a widely recognized system for identifying new virulence determinants and studying the pathogenesis of the organism. Here, we examine how both host factors and P. aeruginosa PAO1 gene expression are affected in planta after infiltration into incompatible and compatible cultivars of tobacco (Nicotiana tabacum L.). N. tabacum has a resistance gene (N) against tobacco mosaic virus, and although resistance to PAO1 infection is correlated with the presence of a dominant N gene, our data suggest that it is not a factor in resistance against PAO1. We did observe that the resistant tobacco cultivar had higher basal levels of salicylic acid and a stronger salicylic acid response upon infiltration of PAO1. Salicylic acid acts as a signal to activate defense responses in plants, limiting the spread of the pathogen and preventing access to nutrients. It has also been shown to have direct virulence-modulating effects on P. aeruginosa. We also examined host effects on the pathogen by analyzing global gene expression profiles of bacteria removed from the intracellular fluid of the two plant hosts. We discovered that the availability of micronutrients, particularly sulfate and phosphates, is important for in planta pathogenesis and that the amounts of these nutrients made available to the bacteria may in turn have an effect on virulence gene expression. Indeed, there are several reports suggesting that P. aeruginosa virulence is influenced in mammalian hosts by the availability of micronutrients, such as iron and nitrogen, and by levels of O2.

* Corresponding author. Mailing address: 1173 Campus Delivery, Department of Horticulture and Landscape Architecture, Colorado State University, Fort Collins, CO 80523-1173. Phone: (970) 491-7170. Fax: (970) 491-7745. E-mail: j.vivanco{at}colostate.edu

{triangledown} Published ahead of print on 18 July 2008.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, September 2008, p. 5784-5791, Vol. 74, No. 18
0099-2240/08/$08.00+0     doi:10.1128/AEM.00860-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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