a. Structural comparisons of the PVL phages. Structures of phi7401PVL and phiSa2mw are illustrated based on the nucleotide sequences deposited in databases DDBJ/EMBL/GenBank under accession nos. BA000033 for phiSa2mw and AP012341 for phi7401PVL. Red arrowhead indicates the location of attP. Black bars indicate the locus of amplified DNA fragments using 5 sets of primers. Green bars indicate the locus of amplified DNA fragment identifying the carriage of gene linkages in phi7401PVL. ORFs are colored as follows: orange, ORFs related to lysogeny; red, a ORF in DNA replication/recombination region with assigned functions; bright green, ORFs related to capsid formation; yellowish orange, ORFs related to head formation; yellowish green, ORFs related to tail formation; blue, ORFs related to cell lysis; black, lukS-PV and lukF-PV. The locations of the primers are indicated in lines flanked by arrow heads. Nucleotide sequences of the primers are listed in Additional file 2: Table S2. b. Comparisons of the two phage genomes with a dot plot analysis. The genome sequence of phi7401PVL was compared to those of phiPVL (group 1 cos-site Siphoviridae), phiSa2mw (group 2 cos-site Siphoviridae), and phiN315 (group 3 cos-site Siphoviridae) using a specialized BLAST at NIBI (http://blast.ncbi.nlm.nih.gov/Blast.cgi). Ordinate indicates the genome phi7401PVL. Abscissa indicates the genomes of three phages, phiPVL, phiSa2mw, and phiN315, in dot plots A, B, and C, respectively.