Laboratory of Bacterial Genetics
Section of Biology: Department of Genetics & Evolution and Unit of Microbiology / Institute of Microbiology (SUPSI)
Dr. Xavier Perret
Université de Genève
Sciences III
Unité de Microbiologie
30 quai Ernest-Ansermet
1211 Genève 4
xavier.perret@unige.ch
+41 22 379 31 17

Background

Insufficient nitrogen is one of the major soil parameters that limit plant growth. That most of the Fabaceae may associate with the nitrogen-fixing soil bacteria know as rhizobia makes these plants capable of growing even in the absence of nitrogen fertilizers. This characteristic, which contributed to the global ecological success of legumes (>20,000 species), also provides an opportunity to use rhizobial inoculants on important crops such as soybean, bean, and chickpea, and thus promote sustainable agricultural practices.

To fix atmospheric nitrogen (N2) for the benefit of host plants, rhizobia must first colonize the intracellular space of specialized plant cells found inside root nodules. The infection that allows free-living rhizobia to enter roots and establish persistent colonies inside nodule cells is strictly controlled by plants. The exchange of many molecular signals between host plants and rhizobia helps discriminate symbiotic from pathogenic bacteria.

Research

Our laboratory explores two facets of these beneficial plant-microbe associations:

1. The natural diversity of rhizobia and their adaptation to specific plant cultivars, and
2. The genetic basis for the exceptional promiscuity of the symbiotic strain Sinorhizobium fredii NGR234.

Projects

Diversity of rhizobia in agricultural or natural ecosystems is poorly explored. We propose to collect plant nodules in selected ecosystems (in Switzerland or abroad), followed by characterization of the rhizobia isolated from nodules. Identification is achieved using diverse molecular techniques, including mass spectrometry and DNA sequence analysis.

For those who prefer to focus on molecular techniques, selected genes of the model strain NGR234 will be inactivated by site-directed mutagenesis. Then, the symbiotic phenotypes of the resulting mutants will be scored on a number of host plants.

Projects for Master thesis are defined together with the applicant, taking into a his/her primary interests as well as research currently underway in the laboratory.