Abstract
At least 40 toxin subtypes of botulinum neurotoxins (BoNTs), a heterogenous group of bacterial proteins, are produced by seven different clostridial species. A key factor that drives the diversity of neurotoxigenic clostridia is the association of bont gene clusters with various genomic locations including plasmids, phages and the chromosome. Analysis of Clostridium sporogenes BoNT/B1 strain CDC 1632, C. argentinense BoNT/G strain CDC 2741, and Clostridium parabotulinum BoNT/B1 strain DFPST0006 genomes revealed bont gene clusters within plasmid-like sequences within the chromosome or nested in large contigs, with no evidence of extrachromosomal elements. A nucleotide sequence (255,474 bp) identified in CDC 1632 shared 99.5% identity (88% coverage) with bont/B1-containing plasmid pNPD7 of C. sporogenes CDC 67071; CDC 2741 contig AYSO01000020 (1.1 MB) contained a ~140 kb region which shared 99.99% identity (100% coverage) with plasmid pRSJ17_1 of C. argentinense BoNT/G strain 89G; and DFPST0006 contig JACBDK0100002 (573 kb) contained a region that shared 100% identity (99%) coverage with the bont/B1-containing plasmid pCLD of C. parabotulinum Okra. This is the first report of full-length plasmid DNA-carrying complete neurotoxin gene clusters integrated in three distinct neurotoxigenic species: C. parabotulinum, C. sporogenes and C. argentinense.
Highlights
Botulinum neurotoxins (BoNTs) are extremely potent bacterial proteins produced in a variety of clostridial species
This study describes the rare integration of entire plasmid sequences of ~150–250 kb within the chromosomes of bacteria from three clostridial species (C. sporogenes, C. argentinense, and C. parabotulinum) using homologous recombination processes that are similar to those responsible for bont gene cluster integrations
24 C. sporogenes strains have been identified in the National Center for Biotechnology Information (NCBI) database that carry bont/B genes [20,23,24,25]
Summary
Botulinum neurotoxins (BoNTs) are extremely potent bacterial proteins produced in a variety of clostridial species. While the mechanism of activity of the toxins and the clinical presentation of botulism is consistent, the proteins themselves differ by as much as 70% in amino acid sequence. Seven serotypes and over 40 toxin subtypes have been described [1]. Botulinum neurotoxin (bont) genes have been identified within seven distinct clostridial species [2]. Clostridium parabotulinum, a previously used species designation for proteolytic clostridia that produce BoNT/A, BoNT/B, or BoNT/F, is used here to describe that particular genospecies. This species is sometimes listed as C. botulinum group I. The six additional genospecies are Clostridium botulinum (or C. botulinum group II), Clostridium novyi sensu lato (or C. botulinum group III), Clostridium argentinense, Clostridium baratii, Clostridium butyricum, and Clostridium sporogenes
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