The confirmation that the 21-bp region corresponds to the attP site was obtained by sequencing the DNA of the phage circular forms. The genome of ϕSpn_200 includes a total of 47 ORFs organized into five modules: the lysogeny, the

replication, the packaging, the structural, and the lytic modules (Figure 5A). Such modular organization, especially the presence of closely arranged lysogeny-related genes, resembled that of the Siphoviridae family infecting low-GC content Gram-positive bacteria [50]. The predicted ORFs were compared with sequences from protein Erismodegib in vitro databases and the regions of homology of the ϕSpn_200 genome are described in detail in the Additional file 4. Figure 5 Characterization of ϕSpn_200. A) Genomic organization of ϕSpn_200 prophage. The colors of the ORFs (arrows) of ϕSpn_200 are in accordance with their predicted function: violet refers to genes involved in lysogeny, yellow to genes involved in replication/immunity, fuchsia to genes involved in packaging, turquoise to genes involved in the structure and orange to genes involved in lysis. Some of the proteins indicated are described in the text. Blue arrows at both CP-690550 supplier ends of the prophage indicate the ORFs of the host chromosome. B) Detection of phage particles in the supernatant of

strain AP200 induced to lysis by mitomycin C. Electron micrographs show: several viral particles (left) and a single phage RG7112 concentration particle with a collar structure (arrow) and a slightly bent tail (right). The lysogeny module is located immediately

downstream of the left-end att site; it is composed of the integrase, belonging to the family of tyrosine recombinases, the Cro/CI-like transcriptional regulator and the repressor involved in suppression of the phage lytic cycle (Figure 5A). The second module carries genes with regulatory functions implicated in the replicative processes. The third module includes genes implicated in the packaging Mannose-binding protein-associated serine protease of the phage genome concatemers into the empty capsid shell, such as the large terminase gene. The structural region encodes the morphogenetic proteins involved in the head and tail assembly. Among these proteins, it is noteworthy the presence of PblB that corresponds to the phage tail fiber, involved in tail/host recognition. This protein is also considered a phage-encoded virulence factor [51]. In Streptococcus mitis, PblB is carried by the bacteriophage SM1 and together with PblA, a protein that is missing in ϕSpn_200, it can enhance binding of the microorganism to platelets [51, 52]. No other potential virulence factor was identified in ϕSpn_200, but it must be considered that no function was assigned to 28 out of 47 phage ORFs.