Nod factor modifications mediated by nodZ and nolL gene products (fucosylation and acetylation of fucose residues, respectively) were probably later acquisitions in the nodulation process. Novel phylogenetic analyses suggest that nodZ and nolL genes were transferred from Bradyrhizobium to other nodule bacteria. These bradyrhizobial genes are highly diverse while rhizobial, sinorhizobial and mesorhizobial nodZ and nolL genes are represented by few branches among those from bradyrhizobia. These genes in novel rhizobial backgrounds may have favored efficient nodulation in legume hosts commonly associated with Bradyrhizobium strains.