Eric Baehler

Thème de recherche: Suppression of plant deseases by beneficial soil bacteria

In my PhD thesis, I mainly focus on the study of the regulation of antibiotic compounds produced by the biocontrol agent Pseudomonas fluorescens strain CHA0 by using a novel reporter system based on fluorescent proteins

Indeed this bacterium can protect various crop plants against soil-borne plant pathogens such as fungi, nematodes or other bacteria, and the primary mechanism considered to be responsible for this effective biocontrol capacity is the production of antibiotic compounds such as 2,4-diacetyphloroglucinol (DAPG), pyoluteorin (PLT), pyrrolnitrin and hydrogen cyanide. The regulation of the biosynthesis of these secondary metabolites is quite complex but it is known that it involves the two-component system GacS/GacA, sigma factors such as RpoD, RpoS and RpoN, specific pathway regulators and several biotic or abiotic signals. I am looking for new elements which are implicated in this regulation.

In order to study this regulation in the rhizosphere, i.e. at the site of pathogen suppression, I have developed a reporter system based on the autofluorescent green (GFP) and red (DsRed) proteins. This system allowed me to confirm that a fine-regulated balance between DAPG and PLT occurs and that it is affected by other phenolic compounds such as the plant-phenolic salycilate. Combined with flow cytometry and fluorescence microscopy, this new reporter system allows me to monitor the expression of antibiotic biosynthetic genes in situ and I expect to get more insight of what really happens in the rhizosphere.

Since December 2000
PhD student and assistant at the Department of Fundamental Microbiology, Lausanne University, Switzerland. Subject: Regulation of antibiotic production in the biocontrol agent Pseudomonas fluorescens CHA0.

1995 - 2000
Diplôme de biologiste (equivalent to a Master degree) in Microbial Ecology with specializations in Microbiology, Botany and Ecology, Lausanne University, Switzerland. (Title of the diploma thesis: Importance de RpoE chez Pseudomonas fluorescens CHA0 face à différents stress environnementaux et dans la capacité de biocontrôle de cette souche).

1. Schnider-Keel, U., Bang Lejbølle, K., Baehler, E., Haas, D., and Keel, C. 2001. The sigma factor AlgU (AlgT) controls exopolysaccharide production and tolerance towards desiccation and osmotic stress in the biocontrol agent Pseudomonas fluorescens CHA0. Appl. Environ. Microbiol. 67: 5683-5693.

2. Maurhofer, M., Baehler, E., Notz, R. Martinez, V., and Keel, C. 2004. Cross talk between 2,4-diacetylphloroglucinol-producing biocontrol pseudomonads on wheat roots. Appl. Environ. Microbiol. 70: 1990-1998.

3. Baehler, E., Bottiglieri, M., Péchy-Tarr, M., Maurhofer, M., and Keel, C. 2005. Use of green fluorescent protein-based reporters to monitor balanced production of antifungal compounds in the biocontrol agent Pseudomonas fluorescens CHA0. J. Appl. Microbiol. (in press).