Scientists say they have come across a surprising discovery showing how a specific virus that attacks Escherichia coli bacteria delivers its DNA during the infection process. This is according to a study published in the journal Nature.

Researchers from Purdue University, the University of Arizona and the University of Texas at Austin say the newly discovered process occurs in the virus phiX174 - a bacteriophage that attacks E. Coli bacteria.

The phiX174 bacteriophage is part of a group of viruses that have no distinct tail sections to enable transfer of their DNA to host cells, the investigators explain. But they were surprised to find that phiX174 seems to produce its own temporary tail for this process.

"It doesn't carry its tail around with it, but when it is about to infect the host it makes a tail," says Michael Rossmann, of Purdue University and one of the study authors.

The investigators say that another bacteriophage called T7 possesses a short tail, and this becomes longer as it infects host cells. But they note that the process found in the phiX174 virus has never been seen before.

They explain that the tail is very fast in its work, and it is likely to have gone undiscovered because it quickly emerges and disappears just as fast.

Explaining the findings to Medical News Today, Rossman said:

"Most bacterial viruses assemble a tail that forms part of the infectious viral particle. Apparently phiX 174 is no different, except the tail is assembled only at the time of infection, not at the time of head capsid infection.

Thus the evolution of viruses on Earth has probably gone through a common process that involved the formation of tails. Life as we know it today could not have happened without the assistance of viruses to mix and match genes."

The investigators mutated the phiX174 virus, preventing it from creating the tail. After this, it could no longer infect host cells.

How the tail is created

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The H protein of the phiX174 virus produces a temporary tail (in red), which delivers its DNA to the E. Coli cells (purple) during the infection process.
Image credit: Lei Sun, Purdue University.

Explaining their findings in detail, the researchers say the capsid of the virus - its outer shell - consists of four proteins - H, J, F and G. The structures of the H protein had not been determined previously, although structures of all other proteins had.

Findings from this study revealed that it is the H protein that creates the tail, also referred to as a "tube-shaped structure."

Using an imaging method called cryo-electron tomography, it was found that the structure has two ends, both of which infect the E. Coli cells by attaching themselves to the cell's inner and outer membranes.

Further analysis revealed that the H-protein tube is made up of 10 "alpha-helical" molecules that wrap around each other.

Additionally, a lining of amino acids was discovered in the tube, which the researchers say is perfect for the transfer of DNA into the E. Coli cells.

Rossman says:

"This may be a general property found in viral-DNA conduits and could be critical for efficient genome translocation into the host."

Rossman told Medical News Today that the next steps from this research will involve determining when and where the phiX174 tail assembles.

Medical News Today recently reported on the discovery of bacteriophages that target Clostridium difficile - an infectious hospital bug.