Applied and Environmental Microbiology, December 2001, p. 5761-5770, Vol. 67, No. 12
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.12.5761-5770.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Lehrstuhl für Mikrobiologie, Technische Universität München, D-85350 Freising,1 and Institut für Biochemische Pflanzenpathologie2 and Institut für Bodenökologie,3 GSF-Forschungszentrum, D-85764 Neuherberg, Germany, and Department of Microbiology, DTU, DK-2800 Lyngby, Denmark4
Received 4 June 2001/Accepted 12 September 2001
Given that a large proportion of the bacteria colonizing the roots of plants is capable of producing N-acyl-L-homoserine lactone (AHL) molecules, it appears likely that these bacterial pheromones may serve as signals for communication between cells of different species. In this study, we have developed and characterized novel Gfp-based monitor strains that allow in situ visualization of AHL-mediated communication between individual cells in the plant rhizosphere. For this purpose, three Gfp-based AHL sensor plasmids that respond to different spectra of AHL molecules were transferred into AHL-negative derivatives of Pseudomonas putida IsoF and Serratia liquefaciens MG1, two strains that are capable of colonizing tomato roots. These AHL monitor strains were used to visualize communication between defined bacterial populations in the rhizosphere of axenically grown tomato plants. Furthermore, we integrated into the chromosome of AHL-negative P. putida strain F117 an AHL sensor cassette that responds to the presence of long-chain AHLs with the expression of Gfp. This monitor strain was used to demonstrate that the indigenous bacterial community colonizing the roots of tomato plants growing in nonsterile soil produces AHL molecules. The results strongly support the view that AHL signal molecules serve as a universal language for communication between the different bacterial populations of the rhizosphere consortium.
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