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Chapter 13 : Clostridium botulinum
Category: Applied and Industrial Microbiology; Food Microbiology
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Genetic analysis focused on BoNT genes and flanking genes, which elucidated the botulinum locus encompassing the genes encoding BoNT, associated nontoxic proteins, and the regulator Bot/R, and provided evidence of its variation among the different toxinotypes. Whole genomes sequencing is now available for eight Clostridium botulinum strains and is in progress for several other strains. These sequence data will allow us to get deeper insights into the lifestyle of C. botulinum—in particular, its survival in the environment and in food products, as well as its regulation of toxin production and also permit us to better understand its relationship with related nontoxigenic clostridia and the modes of transfer of toxin genes. The neurotoxin and ANTP genes are clustered in close vicinity and constitute the botulinum locus. Indeed, two main types of botulinum locus can be distinguished, the HA locus containing ntnh and ha genes and the OrfX locus containing orf X, p47, and ntnh genes in addition to the bont gene. The upstream regions of the botulinum locus are identical in the genome of the three C. botulinum A1 strains and contain a flagellin gene. Bacteriophages mediate the neurotoxin gene transfer in group III of C. botulinum. In vitro transcription, transcripts were observed when BotR/A-Core was incubated only with DNA templates containing ntnh-bont/A and ha35 promoters. Thus, BotR/A is an alternative sigma factor required for specifc expression of the botulinum locus operons.
Key Concept Ranking
- Multiple-Locus Variable-Number Tandem-Repeat Analysis
- Transcription Start Site
The number of putative orthologous genes in Clostridium botulinum and other clostridia. The number of putative orthologous genes between C. botulinum type A strain Hall, C. tetani strain E88, C. perfringens strain 13, C. difficile strain 630, and C. acetobutylicum is shown, according to reference 106 .
Genome comparison of eight C. botulinum strains. A bidirectional blast (blastP) was performed, comparing all protein sequences of the C. botulinum F strain to the seven other C. botulinum genomes. Outer circle: all predicted open reading frames of strain Langeland, plotted according to DNA strand location. The next seven circles represent, from outside to inside, the genomes of the A strains ATCC19397, Hall, ATCC3502, the A3 strain Loch Maree, the B1 strain Okra, the B strain Eklund 17B, and the E3 strain Alaska E43, respectively. Light grey: shared “backbone” (protein identity >90%). Dark grey: absent genes (protein identity of <10%). Medium grey: divergence (between 10 and 90% protein identity).
Different gene organization of botulinum loci in C. botulinum type A strains.
Gene organization of botulinum loci in C. botulinum type B to G strains.
Flanking regions of botulinum loci in C. botulinum type A and B strains.
Homologies at amino acid sequence level and mosaic structures of NTNH from HA and OrfX loci indicating that the ntnh gene might be a hot spot for recombination events. Percentage values are amino acid sequence identities. Black boxes show high homology levels, and grey boxes lower homology levels.
Phylogenetic tree of BoNT types according to their amino acid sequence relatedness and the UPGMA method. (A) Main BoNT types: BoNT/A1 (strain Hall); BoNT/B2 (strain ATCC7949); BoNT/Bnp (strain Eklund17B); BoNT/C (strain 468); BoNT/D (strain 1873); BoNT/CD (strain 6813); BoNT/E1 (strain Beluga); BuNT/E4 (strain ATCC43755); BoNT/F (strain Langeland); BoNT/Fnp (strain 202F); BoNT/G (strain NCFB3012). (B) BoNT/A subtypes: BoNT/A1 (strain Hall); BoNT/A2 (strain Kyoto F); BoNT/A3 (strain Loch Maree); BoNT/A4 (strain 657); BoNT/A5 (strain HO 4402 065). (C) Main BoNT/B subtypes: BoNT/B1 (strain NCTC7273); BoNT/B2 (strain ATCC7949); BoNT/B3 (strain CDC795); BoNT/Bnp (strain Eklund17B), bivalent BoNT/B (strain Ba657).
Groups of botulinum neurotoxin-producing clostridia, produced toxins, and main properties
Main characteristics of C. botulinum genomes a
Main characteristics of plasmids from six C. botulinum strains a
Main characteristics of C. botulinum C phage
Number of genes putatively acquired by horizontal gene transfer (HGT) in C. botulinum genomes a
Putative proteases from C. botulinum strain Hall ( 117 )