BoNT complex and flanking regions in different strains. The bont gene cluster, flanking regions and location (chromosome or plasmid) are indicated for the different strains. The orfX cluster (orfX3-orfX2-orfX1-(botR)-p47-ntnh-bont complex genes) is present in the BoNT/E-producing strains (C. botulinum and C. butyricum), the BoNT/A1 of the A1(B) strain, serotype F (BoNT/F and BoNT/bvF) and the BoNT/A2-A4 subtypes. The ha cluster (ha70-ha17-ha33-botR-ntnh-bont complex genes) is present in the serotype B strains containing BoNT/bvB, BoNT/B1, npBoNT/B, BoNT/(B) and BoNT/A1 of the Hall strain. The flanking regions consist of IS elements, flagellin (fla), lycA and hypothetical (hypo) proteins. The prime symbol indicates a partial gene.