The Structural Basis of T4 Phage Lysis Control: DNA as the Signal for Lysis Inhibition.

Optimal phage propagation depends on the regulation of the lysis of the infected host cell. In T4 phage infection, lysis occurs when the holin protein (T) forms lesions in the host membrane. However, the lethal function of T can be blocked by an antiholin (RI) during lysis inhibition (LIN). LIN sets if the infected cell undergoes superinfection, then the lysis is delayed until host/phage ratio becomes more favorable for the release of progeny. It has been thought that a signal derived from the superinfection is required to activate RI. Here we report structures that suggest a radically different model in which RI binds to T irrespective of superinfection, causing it to accumulate in a membrane as heterotetrameric 2RI-2T complex. Moreover, we show the complex binds non-specifically to DNA, suggesting that the gDNA from the superinfecting phage serves as the LIN signal and that stabilization of the complex by DNA binding is what defines LIN. Finally, we show that soluble domain of free RI crystallizes in a domain-swapped homotetramer, which likely works as a sink for RI molecules released from the RI-T complex to ensure efficient lysis. These results constitute the first structural basis and a new model not only for the historic LIN phenomenon but also for the temporal regulation of phage lysis in general.

Complete Genome Sequence of Staphylococcus aureus Siphophage Lorac.

Staphylococcus aureus is a leading cause of a wide range of clinical infections. Here, we announce the complete genome sequence of S. aureus siphophage Lorac, a phiETA-like temperate phage that is similar at the nucleotide level to the previously described S. aureus prophage phiNM2.

Complete Genome Sequences of Staphylococcus epidermidis Myophages Quidividi, Terranova, and Twillingate.

Staphylococcus epidermidis is an opportunistic pathogen that commonly colonizes human skin and mucous membranes. We report here the complete genome sequences of three S. epidermidis phages, Quidividi, Terranova, and Twillingate, which are members of the Twort-like group of large myophages infecting Gram-positive hosts.

Fluorescent nanodiamond-bacteriophage conjugates maintain host specificity.

Rapid identification of specific bacterial strains within clinical, environmental, and food samples can facilitate the prevention and treatment of disease. Fluorescent nanodiamonds (FNDs) are being developed as biomarkers in biology and medicine, due to their excellent imaging properties, ability to accept surface modifications, and lack of toxicity. Bacteriophages, the viruses of bacteria, can have exquisite specificity for certain hosts. We propose to exploit the properties of FNDs and phages to develop phages conjugated with FNDs as long-lived fluorescent diagnostic reagents. In this study, we develop a simple procedure to create such fluorescent probes by functionalizing the FNDs and phages with streptavidin and biotin, respectively. We find that the FND-phage conjugates retain the favorable characteristics of the individual components and can discern their proper host within a mixture. This technology may be further explored using different phage/bacteria systems, different FND color centers and alternate chemical labeling schemes for additional means of bacterial identification and new single-cell/virus studies.

Genomic and proteomic features of mycobacteriophage SWU1 isolated from China soil.

Mycobacteriophage SWU1 is a newly isolated phage from soil sample collected in Sichuan province, China using Mycobacterium smegmatis mc(2)155 as host. Plaque, phage morphology and one-step growth curve were characterized. The complete genomic sequence of phage SWU1 was determined by shotgun sequencing. The ends of SWU1 were determined. Structural proteins of SWU1 were analyzed by NanoLC-ESI-MS/MS. Seven ORFs were identified as structural protein encoded by SWU1 genome. The genetic basis underlying the SWU1 plaque was explored using comparative genomics. Prophages homologous to SWU1 were identified in two pathogens, Segniliparus rugosus ATCC BAA-974 and Mycobacterium rhodesiae JS60. Genus Segniliparus is a member of the order Corynebacteriales. To our knowledge, this is the first report of Mycobacterium prophages in different genera.

Efficacy of bacteriophage therapy in a model of Burkholderia cenocepacia pulmonary infection.

The therapeutic potential of bacteriophages (phages) in a mouse model of acute Burkholderia cenocepacia pulmonary infection was assessed. Phage treatment was administered by either intranasal inhalation or intraperitoneal injection. Bacterial density, macrophage inflammatory protein 2 (MIP-2), and tumor necrosis factor alpha (TNF-alpha) levels were significantly reduced in lungs of mice treated with intraperitoneal phages (P < .05). No significant differences in lung bacterial density or MIP-2 levels were found between untreated mice and mice treated with intranasal phages, intraperitoneal ultraviolet-inactivated phages, or intraperitoneal lambda phage control mice. Mock-infected mice treated with phage showed no significant increase in lung MIP-2 or TNF-alpha levels compared with mock-infected/mock-treated mice. We have demonstrated the efficacy of phage therapy in an acute B. cenocepacia lung infection model. Systemic phage administration was more effective than inhalational administration, suggesting that circulating phages have better access to bacteria in lungs than do topical phages.