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Applied and Environmental Microbiology, September 2002, p. 4604-4612, Vol. 68, No. 9
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.9.4604-4612.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Construction and Characterization of a proU-gfp Transcriptional Fusion That Measures Water Availability in a Microbial Habitat{dagger}

Catherine A. Axtell and Gwyn A. Beattie*

Department of Microbiology, Iowa State University, Ames, Iowa 50011

Received 12 February 2002/ Accepted 17 June 2002

We constructed and characterized a transcriptional fusion that measures the availability of water to a bacterial cell. This fusion between the proU promoter from Escherichia coli and the reporter gene gfp was introduced into strains of E. coli, Pantoea agglomerans, and Pseudomonas syringae. The proU-gfp fusion in these bacterial biosensor strains responded in a quantitative manner to water deprivation caused by the presence of NaCl, Na2SO4, KCl, or polyethylene glycol (molecular weight, 8000). The fusion was induced to a detectable level by NaCl concentrations of as low as 10 mM in all three bacterial species. Water deprivation induced proU-gfp expression in both planktonic and surface-associated cells; however, it induced a higher level of expression in the surface-associated cells. Following the introduction of P. agglomerans biosensor cells onto bean leaves, the cells detected a significant decrease in water availability within only 5 min. After 30 min, the populations were exposed, on average, to a water potential equivalent to that imposed by approximately 55 mM NaCl. These results demonstrate the effectiveness of a proU-gfp-based biosensor for evaluating water availability on leaves. Furthermore, the inducibility of proU-gfp in multiple bacterial species illustrates the potential for tailoring proU-gfp-based biosensors to specific habitats.

* Corresponding author. Mailing address: Iowa State University, Department of Microbiology, Ames, IA 50011. Phone: (515) 294-5571. Fax: (515) 294-6019. E-mail: gbeattie{at}iastate.edu.

{dagger} Paper no. 19692 of the Iowa Agriculture and Home Economics Experiment Station, Ames (project no. 3433).

Applied and Environmental Microbiology, September 2002, p. 4604-4612, Vol. 68, No. 9
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.9.4604-4612.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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