Sandrine Ceurstemont, editor, New Scientist TV
In an attack from above, a virus swoops down on a bacterium and pierces it with a mini drill. The tip of the spike then detaches, allowing genetic material to seep in so it can reproduce inside its victim.
The overall process depicted in this animation is well known, but many details still remain a mystery. Now Petr Leiman from the Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland, and his team are filling in pieces of the puzzle by measuring the tiny weapon and uncovering its structure.
By analysing the membrane-drilling spike in a synchrotron, the team found that its tip is a single nanometer in diameter and also contains an iron atom. "Iron-containing proteins have colour, but these spikes were colourless," says Leiman. "We weren't expecting to find that so we took time to make sure."
According to Leiman, iron is likely to help stabilise the protrusion so that it doesn't fall apart. But the discovery opens up new questions about what happens to the weapon during an attack. For example, bacteria like salmonella and Escherichia coli, which the virus targets, have both an outer and inner membrane but whether it penetrates both of them is unknown. "The protein is the plug so it has to come off so that DNA enters the cell," says Leiman. "But we don't know when it comes off."
The team plans to follow up by investigating the rigidity of the spikes and how they work. They will also probe other similar viruses to compare the structure of their weapons.
If you enjoyed this post, you might like to watch bacteria get guided by a magnetic field or see how viruses can hop over infected cells to target healthy ones.