NOD FACTOR THIN-LAYER CHROMATOGRAPHY PROFILING AS A TOOL TO CHARACTERIZE SYMBIOTIC SPECIFICITY OF RHIZOBIAL STRAINS - APPLICATION TO SINORHIZOBIUM-SAHELI, SINORHIZOBIUM-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, Si norhizobium teranga, and the so-called cluster U. A collection of stra ins belonging to these different groups was analyzed in order to deter mine whether the host range of a strain could be correlated with vario us molecular nodulation determinants, Nodulation tests showed that, in dependently of their taxonomic position, all the strains isolated from the same plant genus exhibited a similar host range, which was differ ent for Sesbania and Acacia isolates. The fact that S. teranga strains nodulate either Acacia or Sesbania led us to subdivide this species i nto biovars acaciae and sesbaniae. Thin-layer chromatography (TLC) ana lysis of the Nod factors synthesized by overproducing strains showed t hat (i) strains isolated from the same plant genus exhibited similar T LC profiles and (ii) profiles of Acacia and Sesbania symbionts were ea sily distinguishable, Acacia strains producing, in particular, sulfate d 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 speci fic nod genes. We thus propose that Nod factor TLC profiling may be us ed as an easy and powerful tool for the classification of rhizobial st rains on the basis of their symbiotic properties.