Abstract
BackgroundClostridium botulinum is a taxonomic designation for at least four diverse species that are defined by the expression of one (monovalent) or two (bivalent) of seven different C. botulinum neurotoxins (BoNTs, A-G). The four species have been classified as C. botulinum Groups I-IV. The presence of bont genes in strains representing the different Groups is probably the result of horizontal transfer of the toxin operons between the species.ResultsChromosome and plasmid sequences of several C. botulinum strains representing A, B, E and F serotypes and a C. butyricum type E strain were compared to examine their genomic organization, or synteny, and the location of the botulinum toxin complex genes. These comparisons identified synteny among proteolytic (Group I) strains or nonproteolytic (Group II) strains but not between the two Groups. The bont complex genes within the strains examined were not randomly located but found within three regions of the chromosome or in two specific sites within plasmids. A comparison of sequences from a Bf strain revealed homology to the plasmid pCLJ with similar locations for the bont/bv b genes but with the bont/a4 gene replaced by the bont/f gene. An analysis of the toxin cluster genes showed that many recombination events have occurred, including several events within the ntnh gene. One such recombination event resulted in the integration of the bont/a1 gene into the serotype toxin B ha cluster, resulting in a successful lineage commonly associated with food borne botulism outbreaks. In C. botulinum type E and C. butyricum type E strains the location of the bont/e gene cluster appears to be the result of insertion events that split a rarA, recombination-associated gene, independently at the same location in both species.ConclusionThe analysis of the genomic sequences representing different strains reveals the presence of insertion sequence (IS) elements and other transposon-associated proteins such as recombinases that could facilitate the horizontal transfer of the bonts; these events, in addition to recombination among the toxin complex genes, have led to the lineages observed today within the neurotoxin-producing clostridia.
Highlights
Clostridium botulinum is a taxonomic designation for at least four diverse species that are defined by the expression of one or two of seven different C. botulinum neurotoxins (BoNTs, A-G)
The evidence for the plasmid location of bont/bv b and bont/f is supported by the sequence homology of the four contigs to pCLJ and a detailed examination of the location of the bont/bv b and bont/f is described later. These results show that the Group I C. botulinum A, B and F strains share a similar chromosome organization to each other and to C. sporogenes but not to the Group II nonproteolytic B strain or serotype E strains, the Group VI BoNT/ E-producing C. butyricum or C. tetani
This study, which compares 15 clostridial genomic sequences, was undertaken in order to identify the underlying events that result in the genetic diversity within the C. botulinum species
Summary
Clostridium botulinum is a taxonomic designation for at least four diverse species that are defined by the expression of one (monovalent) or two (bivalent) of seven different C. botulinum neurotoxins (BoNTs, A-G). Clostridium botulinum is a taxonomic designation for at least four diverse groups of Gram positive spore-forming anaerobic bacteria that produce the most potent naturally occurring toxin known, botulinum neurotoxin (BoNT). Production of BoNT has been the single criterion for inclusion within the C. botulinum species and was adopted in order to prevent scientific and medical confusion regarding the intoxication known as botulism. This single criterion has resulted in a species designation that encompasses clades of strains that should be considered as four separate species. Further Group designations (V and VI) have been proposed for other clostridial species found to express BoNT, such as the BoNT/F-producing C. baratii strains and the BoNT/E-producing C. butyricum strains [4]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
