(a) Location of the RarA operon within C. botulinum and C. butyricum strains and (b) dendrogram of rarA genes from different clostridial species. The rarA operon in the ATCC 3502 strain is compared to the rarA operon in the Group II and VI strains. In the Eklund 17B strain the rarA gene is intact. However, in the Alaska 43, Beluga and C. butyricum BL 5262 strains, the rarA gene is split and a bont/e gene cluster has been inserted. Note the similarity of the components within the inserted sequence and that it also contains an intact rarA gene. The regions flanking the rarA operon are similar upstream and downstream in the Group II strains. (b) The dendrogram of rarA genes shows that some strains contain two copies of rarA, one that is intact and one that is split from the insertion of the bont/e complex genes. The 1,195 nucleotides of rarA from both intact and split genes were compared; the sequences of split rarA genes were spliced together to make full-length genes. The dendrogram shows that the sequences of the spliced rarA in C. botulinum Alaska E43 and Beluga type E strains are similar to each other but are different from the spliced rarA in C. butyricum BL 5262. This difference indicates that the insertion of the toxin gene cluster occurred as two separate events in each species. The inserted/intact rarA sequences in both of these species are similar indicating a common source.