Rhizobium leguminosarum biovar phaseoli forms nitrogen-fixing nodules on the roots of the common bean plant. This project aims at the identification and characterization of an autoinducer-triggered environmental sensing system that allows the bacteria to monitor their own population density. Given the fact that rhizobia are densely packed within the nodule, this system may reveal to be essential in bacterium to bacteroid
differentiation, a process that is poorly understood.
The responsible genes of R. Ieguminosarum will be identified by their putative homology with the well-characterized genes of Vibrio fischeri and by phenotypic selection. The isolated genes will be cloned. The expression of these genes in R. leguminosarum will be monitored under free-living and symbiotic conditions. Mutants concerning the autoinducer- relevant genes will be constructed in phenotypically characterized in dependence of the environmental conditions (free-living / symbiotic). Finally
autoinducer-dependent genes will be identified.