Nod factor thin-layer chromatography profiling as a tool to characterize symbiotic specificity of rhizobial strains: Application to Sinorhizobium saheli, S-teranga, and Rhizobium sp strains isolated from Acacia and Sesbania

Rhizobia isolated from Acacia or Sesbania belong to several taxonomic groups, including the newly described species Sinorhizobium saheli, Sinorhizobium teranga, and the so-called cluster U. A collection of strains belonging to these different groups was analyzed in order to determine whether the host range of a strain could be correlated with various molecular nodulation determinants, Nodulation tests showed that, independently of their taxonomic position, all the strains isolated from the same plant genus exhibited a similar host range, which was different for Sesbania and Acacia isolates. The fact that S. teranga strains nodulate either Acacia or Sesbania led us to subdivide this species into biovars acaciae and sesbaniae. Thin-layer chromatography (TLC) analysis of the Nod factors synthesized by overproducing strains showed that (i) strains isolated from the same plant genus exhibited similar TLC profiles and (ii) profiles of Acacia and Sesbania symbionts were easily distinguishable, Acacia strains producing, in particular, sulfated molecules. In contrast, no correlation could be established between the host range of a strain and its plasmid content, the nature of the nod gene inducers or the presence of DNA sequences homologous to specific nod genes. We thus propose that Nod factor TLC profiling may be used as an easy and powerful tool for the classification of rhizobial strains on the basis of their symbiotic properties.