Contribution to the study of the relationship between gammaproteobacteria and rhizobia in legume species of the genus Hedysarum

The nodular contents of the leguminous species of the genus Hedysarum (H. carnosum, H. spinosissimum subsp capitatum and H. pallidum) consist of cultivable bacteria belonging to the class Gammaproteobacteria, while the rhizobia of these leguminous species are not cultivable. Rhizobium sulla is the specific micro-symbiont of the H. coronarium leguminous species. The aim of this study is to see if the Gammaproteobacteria that inhabit the nodules of the three species of the genus Hedysarum (H. carnosum, H. spinosissimum subsp capitatum and H. pallidum) could have acquired the symbiotic criteria from rhizobia and cause nodulation in these host legume species by the transformation process. Transformation is carried out by extracting the plasmid DNA from the R. sulla strain and incorporate it into the bacterial strains of the Gammaproteobacteria class. Nodulation assay is performed to evaluate the ability of transformed strains to cause nodulation in legume species. The results showed that although there has been a transformation, there is a total failure of nodulation in the three legume species. This is explained by the specificity of molecular signals between bacteria and host plants as well as the genetic information carried by the plasmid is not sufficient to achieve a complete symbiotic relationship.