Regulation and release of VSH-1, a prophage and gene transfer agent of Brachyspira hyodysenteriae
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Brachyspira hyodysenteriae is an anaerobic spirochete and an important pathogen of swine. B. hyodysenteriae cells harbor VSH-1, a mitomycin C-inducible prophage that mediates generalized transduction between B. hyodysenteriae strains. VSH-1 virions package random fragments of B. hyodysenteriae chromosomal DNA rather than a viral genome, which has complicated genetic investigations. N-terminal amino acid sequences generated for proteins from purified VSH-1 whole virions and tailless heads facilitated the identification of VSH-1 structural genes and allowed their assignment as head or tail associated. It remained uncertain however, as to whether or not additional genes important to virion production existed within the prophage sequence. While mitomycin C-induction of the VSH-1 prophage resulted in cell lysis pointed to bacteriophage genes for lytic growth, the identity of these genes was unknown. The ability of VSH-1 virions to mediate horizontal gene transfer in B. hyodysenteriae populations coupled with the recent observation that VSH-1 was common among Brachyspira strains suggested that VSH-1 might play an important role in Brachyspira ecology.;This dissertation is a continuation of research on VSH-1 to understand the biology of this bacteriophage. In the following studies, additional VSH-1 genes were identified including an endolysin involved in VSH-1 escape from B. hyodysenteriae cells. The organization of genes for head and tail structures and lytic functions was found to be similar to other bacteriophage operons. Characteristics of VSH-1 transcription were investigated, leading to the identification of an alternative to mitomycin C as VSH-1 inducing agent.