Résumé:
This work is carried out in order to study the bacterial symbiot of the root nodules of two wild legume species endemic to Algeria, Hedysarum naudinianum and Hedysarum perrauderianum. The cultivable isolated bacteria underwent a phenotypical characterization including a series of tests. The aptitude of the isolates to form nodules on the roots of the plants hosts is evaluated by the nodulation test. The profiles of the total proteins of the isolates are determined by electrophoresis SDS-PAGE. The molecular characterization is carried out by DNA-based identity analyses; ARDRA profile sorting and 16S rDNA sequencing. The results show that the nodules of the two legume species included enterobactériaceae having 100% 16S rDNA sequence identity with both Enterobacter cloacae and E. ludwigii. In H. perrauderianum, this taxon was the sole cultured isolate while the other legume H. naudinianum seems to lodge a large range of endophytes. While no culturable Rhizobium could be obtained, several attempts were carried out with the nodules of the two leguminous species. A method based on the cloning and the transformation revealed the existence of Mesorhizobium sp in the two species of Hedysarum. The sequence of Mesorhizobium in H. perrauderianum show identities to other mesorhizobia reported in different legumes from mediterranean to Far East locations. Therefore the sequence of the Mesorhizobium within H. naudinianum bears a mutation which is unique and originates a single nucleotide polymorphism (SNP). Data from the microsymbionts appear to suggest interesting clues to interpret the evolutionary ecology of their host plants.