title: Developmentally-regulated excision of the SPβ prophage reconstitutes a gene required for spore envelope maturation in Bacillus subtilis.
abstract: Temperate phages infect bacteria by injecting their DNA into bacterial cells, where it becomes incorporated into the host genome as a prophage. In the genome of Bacillus subtilis 168, an active prophage, SPβ, is inserted into a polysaccharide synthesis gene, spsM. Here, we show that a rearrangement occurs during sporulation to reconstitute a functional composite spsM gene by precise excision of SPβ from the chromosome. SPβ excision requires a putative site-specific recombinase, SprA, and an accessory protein, SprB. A minimized SPβ, where all the SPβ genes were deleted, except sprA and sprB, retained the SPβ excision activity during sporulation, demonstrating that sprA and sprB are necessary and sufficient for the excision. While expression of sprA was observed during vegetative growth, sprB was induced during sporulation and upon mitomycin C treatment, which triggers the phage lytic cycle. We also demonstrated that overexpression of sprB (but not of sprA) resulted in SPβ prophage excision without triggering the lytic cycle. These results suggest that sprB is the factor that controls the timing of phage excision. Furthermore, we provide evidence that spsM is essential for the addition of polysaccharides to the spore envelope. The presence of polysaccharides on the spore surface renders the spore hydrophilic in water. This property may be beneficial in allowing spores to disperse in natural environments via water flow. A similar rearrangement occurs in Bacillus amyloliquefaciens FZB42, where a SPβ-like element is excised during sporulation to reconstitute a polysaccharide synthesis gene, suggesting that this type of gene rearrangement is common in spore-forming bacteria because it can be spread by phage infection.
authors.affiliation: Research Center of Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Kimihiro
authors.initials: K
authors.lastname: Abe
authors.affiliation: Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Kawano
authors.affiliation: Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Keito
authors.initials: K
authors.lastname: Iwamoto
authors.affiliation: Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Arai
authors.affiliation: Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Maruyama
authors.affiliation: Center for Genomics and Systems Biology, New York University, New York, New York, United States of America.
authors.forename: Patrick
authors.initials: P
authors.lastname: Eichenberger
authors.affiliation: Research Center of Micro-Nano Technology, Hosei University, Koganei, Tokyo, Japan; Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Sato
mesh_terms: D001407:Bacillus / Q000235:genetics; D017103:Bacillus Phages / Q000235:genetics*; D001412:Bacillus subtilis / Q000187:drug effects / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D015967:Gene Expression Regulation, Viral; D015321:Gene Rearrangement; D016685:Mitomycin / Q000494:pharmacology; D009154:Mutation; D039002:Prophages / Q000235:genetics*; D013171:Spores, Bacterial / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D016685:Mitomycin