Conservation of genetic information between different Rhizobium species

Abstract

Transposon mutagenesis was used to generate nodulation (Nod-) and N2 fixation (Fix-) mutants of R. trifolii SU843. Total DNA isolated from mutant clones was digested with EcoR1 and cloned into plasmid pBR322. Recombinants carrying the Tn5 transposon and flanking Rhizobium DNA sequences were used to probe a gene bank prepared from wild-type R. trifolii SU843 and to identify DNA sequences containing Nod+ or Fix+ genes which were capable of restoring biological functions in the mutants by genetic complementation. Cloned nodulation sequences derived from this work were hybridized with EcoR1 digests of DNA from other fast-growing rhozia. The strains used represent several cross-inoculation and DNA homology groups found among these rhizobia. The extent to which individual cloned sequences were conserved varied among strains. In general, clones sequences were most highly conserved between strains belonging to the same homology group as the donor strain and had diverged most in strains classified in homology groups remote from that of the donor.