title: The genome sequence of Clostridium botulinum type C neurotoxin-converting phage and the molecular mechanisms of unstable lysogeny.
abstract: Botulinum neurotoxins (BoNTXs) produced by Clostridium botulinum are among the most poisonous substances known. Of the seven types of BoNTXs, genes for type C1 and D toxins (BoNTX/C1 and D) are carried by bacteriophages. The gene for exoenzyme C3 also resides on these phages. Here, we present the complete genome sequence of c-st, a representative of BoNTX/C1-converting phages. The genome is a linear double-stranded DNA of 185,682 bp with 404-bp terminal direct repeats, the largest known temperate phage genome. We identified 198 potential protein-coding regions, including the genes for production of BoNTX/C1 and exoenzyme C3. Very exceptionally, as a viable bacteriophage, a number of insertion sequences were found on the c-st genome. By analyzing the molecular structure of the c-st genome in lysogens, we also found that it exists as a circular plasmid prophage. These features account for the unstable lysogeny of BoNTX phages, which has historically been called "pseudolysogeny." The PCR scanning analysis of other BoNTX/C1 and D phages based on the c-st sequence further revealed that BoNTX phages comprise a divergent phage family, probably generated by exchanging genomic segments among BoNTX phages and their relatives.
authors.affiliation: Department of Bacteriology, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Sakaguchi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hayashi
authors.forename: Ken
authors.initials: K
authors.lastname: Kurokawa
authors.forename: Keisuke
authors.initials: K
authors.lastname: Nakayama
authors.forename: Kenshiro
authors.initials: K
authors.lastname: Oshima
authors.forename: Yukako
authors.initials: Y
authors.lastname: Fujinaga
authors.forename: Makoto
authors.initials: M
authors.lastname: Ohnishi
authors.forename: Eiichi
authors.initials: E
authors.lastname: Ohtsubo
authors.forename: Masahira
authors.initials: M
authors.lastname: Hattori
authors.forename: Keiji
authors.initials: K
authors.lastname: Oguma
mesh_terms: D001435:Bacteriophages / Q000235:genetics*; D001483:Base Sequence; D015139:Blotting, Southern; D001905:Botulinum Toxins / Q000235:genetics*; D003014:Clostridium botulinum / Q000378:metabolism / Q000821:virology; D040481:Genome Components / Q000235:genetics; D016679:Genome, Viral; D008242:Lysogeny / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D001905:Botulinum Toxins; C096324:botulinum toxin type C