Submitted to: Ph D Dissertation
Publication Type: Other
Publication Acceptance Date: 11/1/2004
Publication Date: 12/1/2004
Citation: Matson, E. 2004. Regulation and release of vsh-1, a prophage and gene transfer agent of brachyspira hyodysenteriae [Ph D Dissertation]. Ames, IA: Iowa State University. 127 p. Interpretive Summary: Swine dysentery can cause extensive damage to herds. The bacteria that cause this disease have unusual properties, and there is evidence that they are capable of extensive sharing of genetic material. This ability to transfer genetic material may alter the potential of these bacteria to cause disease or to resist antibiotic treatment. The studies described in this work characterize the basic genetic structure and organization of a gene transfer system, and provides new information on the gene transfer process.
Technical Abstract: Brachyspira hyodysenteriae is an anaerobic spirochete and an important pathogen of swine. B. hyodysenteriae cells harbor VSH-1, a mitomycin C-inducible prophage that packages random 7.5 kb fragments of host chromosomal DNA rather than a viral genome and mediates generalized transduction between B. hyodysenteriae strains in vitro. Amino acid sequences of proteins from purified VSH-1 particles were used to identify VSH-1 genes. The region of the B. hyodysenteriae chromosome containing the VSH-1 prophage encodes 16.3 kb of DNA associated with VSH-1 function and is organized in gene clusters for head and tail morphogenesis and host cell lysis. Genes responsible for VSH-1 regulation were not identified, however an analysis of VSH-1 transcription revealed that production of a VSH-1 polycistronic mRNA increased during a 3.5 hour period after B. hyodysenteriae cells were exposed to either mitomycin C or hydrogen peroxide. Chemically induced production of VSH-1 mRNA corresponded with a decrease in transcription of a B. hyodysenteriae housekeeping gene (flaA1) and both effects were dependent on de novo protein synthesis. Similar to other bacteriophage systems, our results are consistent with a shift from bacterial to viral transcription that occurs during VSH-1 induction. Although VSH-1 is defective in self-replication, it appears that an as- yet unidentified genetic switch that senses bacterial stress (possibly at the site of infection) is intact and initiates VSH-1 production leading to horizontal gene transfer between B. hyodysenteriae cells.