Plasmid pNGR234α of the broad host-range Rhizobium sp. NGR234 is a patchwork of genes of various origins. The sequence and organisation of loci involved in replication and conjugal transfer are similar to those of Agrobacterium, while the ORFs within the cytochrome P450 cluster closely resemble those of Bradyrhizabium japonicum. Insertion-sequences (IS), which comprise 18% of pNGR234α and are mainly grouped between nucleotides 300,000 to 390,000, divide the replicon into large clusters of functionally related genes: amino acid/peptide catabolism, nitrogen fixation, type III secretion system, etc. In contrast, the nodulation (nod) genes which contain 49 to 61 % G+C, are present in five smaller clusters dispersed over the entire symbiotic plasmid. Together these results suggest that lateral transfer and shuffling of genetic determinants from various origins greatly contributed to the formation of today's pNGR234α.