Competition between beta-rhizobia for legume infection
G. PESSI (1), M. Lardi (2), G. Purtschert (2), A. Gandolfi (2), S. Bolzan de Campos (2), L. Eberl (2) (1) University of Zurich/ Deparment of Plant and Microbial Biology, Switzerland; (2) University of Zürich, Switzerland

The rhizobium-legume symbiosis is of major ecological and economic importance and accounts for two-thirds of the nitrogen fixed globally. Until recently, all known example of symbiotic relationship between legumes and prokaryotes were confined to the phylogenetically diverse alpha-rhizobia (alpha-proteobacteria). This changed with the discovery of certain beta-proteobacteria of the genera Cupriavidus and Burkholderia (beta-rhizobia), which are also capable of establishing nitrogen-fixing symbiosis with legumes. Previous reports showed that certain legumes can be nodulated by both alpha- and beta-rhizobia and suggested the existence of genetic and physiological factors that determine the preference of Mimosa spp. for beta- rhizobia. In this study, we investigated the capacity of seven beta-rhizobial strains to compete for nodulation of different legumes such as Mimosa pudica (mimosa), Vigna unguiculata (cowpea), Phaseolus vulgaris (bean) and Macroptilium atropurpureum (siratro). While Burkholderia phymatum was found to be the most competitive strain on three out of the four tested legumes (M. pudica, V. unguiculata and P. vulgaris), B. tuberum was the most successful strain on M. atropurpureum. We are currently performing in vitro competition tests using differentially tagged beta-rhizobial strains (dsred and GFP) as well as competition experiments between beta- and alpha-rhizobial strains for legumes infection.

Abstract Number: P2-44
Session Type: Poster