Gene organization and correlation of Nod factor biosynthetic genes in each Sinorhizobium species. Blue arrows indicate the genes encoding enzymes for Nod factor synthesis commonly detected in all tested Sinorhizobium strains. Yellow arrows indicate the genes involved in Nod factor secretion. Green arrows indicate specifically detected genes involved in Nod factor synthesis in an individual species. Red arrows indicate the genes encoding transcriptional regulators of nodulation genes. White arrows indicate genes involved in Nod factor biosynthesis that are not in common.