There are estimated to be on the order of 1010 phage per liter of sea water and roughly 1024 phage infections per second. Despite the frequency of phage infection and its ecological importance, relatively little is known about the molecular mechanics of the infection process. Questions such as what provides the driving force for genome exit from the capsid, what signals the conduit to open to allow exit and how the nucleic acid enters the host cell during infection remain unanswered. However, advances in electron microscopy and image analysis are allowing us to capture a glimpse of this remarkable process. The T7-like podovirus P-SSP7 infects Prochlorococcus marinus, the most abundant photosynthetic microorganism. A recent cryo-electron microscopy study provides insight into the molecular details of the P-SSP7 infection process, and given the similarity between P-SSP7 and other podoviruses is likely to provide a paradigm for understanding the process of phage infection.
Mind the Gap: How Some Viruses Infect Their Hosts. (2010) Viruses 2(11): 2536-2540; doi:10.3390/v2112536
Cryo-electron microscopy (Cryo-EM) and cryo-electron tomography (Cryo-ET) provide structural insights into complex biological processes. The podoviridae are dsDNA containing phage with short, non-contractile tails which nevertheless translocate their DNA into the cytoplasm of their host cells. Liu et al.  used a combination of cryo-EM and cryo-ET to study the structural changes accompanying infection of P. marinus by the phage P-SSP7 and thereby provide unique molecular insight into the process by which the DNA transits from phage to host during infection.