Researchers from the University of Maryland Baltimore County (UMBC) have discovered that mobile genetic elements (MGEs), also known as virus-like entities, attach themselves to helper viruses during intracellular invasion. Until now, it was not known that MGEs could get so close to their helpers.

MGEs are fragments of genes and proteins that rely on the host organism’s cellular machinery to reproduce. They are like thieves that intrude on cellular heists, taking advantage of the hijacking to further their own interests while occasionally benefiting their hosts.

The study focused on a type of MGE called satellite nucleic acid. These sequences lack the codes to produce critical elements and need the presence of other viruses to manufacture their machinery. Enterobacteria phage P4 is an example of a helper virus that can either insert itself into a cell’s genome or exist as extranuclear DNA.

When Enterobacteria phage P4 shares the host with Enterobacteria phage P2, P2 coats P4 with proteins, encapsulating the satellite nucleic acid fragments. The cell eventually bursts, releasing the satellite phages to infect new territory.

In the study, the researchers discovered satellite phages attacking a species of Streptomyces bacterium. Unlike Enterobacteria phage P4s, this phage can produce its own coat but lacks a structure called “pants” needed to enter a host’s cell wall and membranes. Therefore, it requires its own helper.

Electron microscope images revealed that the satellite phages were using their tails to grab ahold of the larger helper phages. Approximately 40 out of the 50 helper phages observed had a satellite attached to them, while frayed remnants of fibers could be seen around the throats of the remaining 10 helper phages.

The researchers also found that the satellite phages lacked the ability to insert their genes into the host’s genome. This explains why they attach to the necks of helper viruses, ensuring their entry into the cell simultaneously.

The discovery of this phenomenon raises the possibility that there may be numerous other satellite-helper systems existing in the microscopic universe. The study was published in The ISME Journal.