Submitted to: Journal of Bacteriology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/10/2004
Publication Date: 2/1/2005
Citation: Frye, J.G., Porwollik, S., Blackmer, F., Cheng, P., Mcclelland, M. 2005. Host gene expression changes and dna amplification during temperate phage induction. Journal of Bacteriology. 187(4):1485-1492. Interpretive Summary: Phage are viruses that infect bacteria either killing them or integrating into their chromosome. Phage integrated into the host chromosome can also be induced to replicate and kill the host bacteria. Because they kill bacteria, phage have been used to prevent or cure bacterial infections. Before phage can be developed into reliable probiotics, their behavior during induction, replication and killing must be better characterized. To investigate this, DNA microarrays were used to measure phage and host gene expression and gene content during phage induction. Phage gene amplification was detected and several phage were also shown to amplify host genes flanking their integration site, a phenomenon termed “escape replication”. Further experiments found that deleting certain phage genes could induce escape replication in other phage. These findings improve the understanding of phage physiology and have impact on the development of phage as safe and reliable probiotics for the control of pathogenic bacteria.
Technical Abstract: Salmonella enterica serovar Typhimurium LT2 harbors four temperate prophage. The lytic cycle of these phage was induced with hydrogen peroxide or mitomycin C. Microarray analysis was used to monitor the increase in phage genome copy number and the changes in RNA expression. Phage gene transcription was classified temporally, and host genes that responded to hydrogen peroxide, mitomycin C, or phage induction were also identified. A region of the Typhimurium LT2 host genome encompassing hundreds of genes, flanking the Fels-1 lambdoid prophage, was amplified many-fold during lytic induction, presumably due to Fels-1 run-off replication prior to excision, a phenomenon termed “escape replication”. An excisionase (xis) mutant of Fels-1 also induced escape replication, but does not get packaged presumably because it does not excise from the host genome. Gifsy-1, a lambdoid prophage that does not normally produce escape replication, did so after the deletion of either its integrase or excisionase genes. Escape replication is probably widespread: large regions of host genome amplification were also observed after phage induction in Typhimurium strains SL1344 and 14028s, at the suspected integration site of prophage genomes.