title: YMC-2011, a Temperate Phage of Streptococcus salivarius 57.I.
abstract: Streptococcus salivariusis an abundant isolate of the oral cavity. The genome ofS. salivarius57.I consists of a 2-Mb chromosome and a 40,758-bp circular molecule, designated YMC-2011. Annotation of YMC-2011 revealed 55 open reading frames, most of them associated with phage production, although plaque formation is not observed inS. salivarius57.I after lytic induction using mitomycin C. Results from Southern hybridization and quantitative real-time PCR confirmed that YMC-2011 exists extrachromosomally, with an estimated copy number of 3 to 4. Phage particles were isolated from the supernatant of mitomycin C-treatedS. salivarius57.I cultures, and transmission electron microscopic examination indicated that YMC-2011 belongs to theSiphoviridaefamily. Phylogenetic analysis suggests that phage YMC-2011 and thecos-type phages ofStreptococcus thermophilusoriginated from a common ancestor. An extended -10 element (pL) and a σ70-like promoter (pR) were mapped 5' to Ssal_phage00013 (encoding a CI-like repressor) and Ssal_phage00014 (encoding a hypothetical protein), respectively, using 5' rapid amplification of cDNA ends, indicating that YMC-2011 transcribes at least two mRNAs in opposite orientations. Studies using promoter-chloramphenicol acetyltransferase reporter gene fusions revealed that pR, but not pL, was sensitive to mitomycin C induction, suggesting that the switch from lysogenic growth to lytic growth was controlled mainly by the activity of these two promoters. In conclusion, a lysogenic state is maintained inS. salivarius57.I, presumably by the repression of genes encoding proteins for lytic growth.IMPORTANCEThe movement of mobile genetic elements such as bacteriophages and the establishment of lysogens may have profound effects on the balance of microbial ecology where lysogenic bacteria reside. The discovery of phage YMC-2011 fromStreptococcus salivarius57.I suggests that YMC-2011 andStreptococcus thermophilus-infecting phages share an ancestor. AlthoughS. salivariusandS. thermophilusare close phylogenetically,S. salivariusis a natural inhabitant of the human mouth, whereasS. thermophilusis commonly found in the mammary mucosa of bovine species. Thus, the identification of YMC-2011 suggests that horizontal gene transfer via phage infection could take place between species from different ecological niches.
authors.affiliation: Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Wen-Chun
authors.initials: WC
authors.lastname: Chou
authors.affiliation: Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.
authors.forename: Szu-Chuan
authors.initials: SC
authors.lastname: Huang
authors.affiliation: Molecular Infectious Disease Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Cheng-Hsun
authors.initials: CH
authors.lastname: Chiu
authors.affiliation: Department of Microbiology and Immunology, College of Medicine, Chang Gung University, Taoyuan, Taiwan mchen@mail.cgu.edu.tw.|Graduate Institute of Biomedical Sciences, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Research Center for Pathogenic Bacteria, College of Medicine, Chang Gung University, Taoyuan, Taiwan.|Molecular Infectious Disease Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Yi-Ywan M
authors.initials: YM
authors.lastname: Chen
mesh_terms: D001483:Base Sequence; D004279:DNA, Viral / Q000235:genetics; D008242:Lysogeny / Q000187:drug effects / Q000235:genetics*; D016685:Mitomycin / Q000494:pharmacology*; D009055:Mouth / Q000382:microbiology; D011401:Promoter Regions, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D017108:Streptococcus Phages / Q000145:classification / Q000235:genetics*; D000070001:Streptococcus salivarius / Q000235:genetics / Q000302:isolation & purification / Q000821:virology*; D014775:Virus Activation / Q000187:drug effects*
chemical_list: D004279:DNA, Viral; D016685:Mitomycin
keywords: Siphoviridae family; Streptococcus salivarius; lysogeny; plasmid; temperate phage