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Recombination and Insertion Events Involving the Botulinum Neurotoxin Complex Genes in Clostridium botulinum Types A, B, E and F and Clostridium butyricum Type E Strains

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Background. C. 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 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. Results. Chromosome 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. Comparison of sequences from a Bf strain revealed homology to the plasmid pCLJ with similar locations for the bontbv b genes but with the bonta4 gene replaced by the bontf gene. 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 bonta1 gene into the serotype toxin B ha cluster, resulting in a successful lineage commonly associated with foodborne botulism outbreaks. In C. botulinum type E and C. butyricum type E strains the location of the bonte 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.

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  • Genetic Engineering and Molecular Biology
  • Medicine and Medical Research

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