Etude Structurale et Génétique des Exopolysaccharides produits par l’espèce Rhizobium sullae

Abstract

Specific and complex interactions between soil bacteria, known as rhizobia, and their leguminous host plants result in the development of root nodules. This process implies a complex dialogue between the partners. Rhizobia synthesize different classes of polysaccharides: exopolysaccharides (EPS), Kdo-rich capsular polysaccharides (KPS), lipopolysaccharides (LPS) and cyclic glu cans. These polymers are crucial for establishing a successful symbiosis with legumes. In this work we focused on studying the EPS produced by Rhizobium sullae bacteria that nodulate Hedysarum coronarium L. largely distributed in Algeria. An unusual fucose rich polysaccharide has been characterized. This desoxysugar showed a significant symbiotic activity on nodulation capacity. Mutant strains of the R. sullae species deficient in EPS production are transformed by plasmid DNA extracted from wild-type strains by a method of thermal shock. Use of calcofluor was used to select transformed bacteria and the incorporation of plasmid DNA was confirmed by carrying a plasmid profil of the agarose gel (1%). The insertion of plasmid DNA restored the ability of EPS production by the transformed strains and consequently their ability to nodulate the plant host. Finally, the symbiotic activity of High molecular weight (HMW) EPS and low molecular weight (LMW) tested with mutant strains. The results show that the LMW EPS are symbiotically more active than HMW EPS.