Researchers from the University of Massachusetts Chan Medical School have recently discovered a unique bacteriophage, P74-26, nicknamed as the Rapunzel bacteriophage. This bacteriophage preys on one of the toughest bacteria on the planet, Thermus thermophilus and is naturally found in inhospitable hot springs. The unique morphology of this phage was that it had an extremely long tail, in comparison to those already known.
P74-26 phage the Rapunzel bacteriophage
The P74-26 phage belongs to the family of Siphoviridae, double-stranded DNA phages, with flexible tail-like structure that allows them to attach to and penetrate bacterial cells, and belong to the Caudovirales order. Morphologically, it has a tail nearly 1 micrometre in length, which is x10 times longer than most bacteriophages.
The mechanism by which the Rapunzel bacteriophage kills bacteria was investigated. They found that the virus produces a protein called endolysin that causes the bacterial cell membrane to break down, leading to the death of the cell. The endolysin protein has a unique shape that differs from other known endolysins, which could potentially make the Rapunzel bacteriophage more effective at killing bacteria than other phages.
“Each phage tail is made up of many small building blocks that come together to form a long tube,” said Emily Agnello, a graduate student at the University of Massachusetts Chan Medical School. “Our research finds that these building blocks can change shape, or conformation, as they come together. This shape-changing behaviour is important in allowing the building blocks to fit together and form the correct structure of the tail tube.”
Using the cryo-electron microscopy, the team where able to capture the bacteriophage’s tail tubes and study how the building block fit together. The researchers were than able to identify that the Rapunzel bacteriophage used a ‘ball and socket’ mechanism to sturdy itself. Additionally, they were able to see that the phage’s tail is formed vertically, by stacking rings of molecules, creating a hollow canal.
“I like to think about these phage building blocks as kind of like Legos. The Lego has studs on one side and the holes or sockets on the other,” said Dr. Brian Kelch, a researcher at the University of Massachusetts Chan Medical School. “Imagine a Lego where the sockets start off closed. But as you start to build with the Legos, the sockets begin to open up to allow the studs on other Legos to build a larger assembly. This movement is an important way that these phage building blocks self-regulate their assembly.”
In comparison with most bacteriophages, the Rapunzel bacteriophage utilizes half the number of building blocks to form stacking rings that make up the tail. “We think what has happened is that some ancient virus fused its building blocks into one protein. Imagine two small Lego bricks are fused into one large brick with no seams. This long tail is built with larger, sturdier building blocks, and we think that could be stabilizing the tail at high temperatures” Dr. Kelch said.
The findings on the P74-26 bacteriophage’s structure have important implications for the field of phage therapy, which aims to use bacteriophages to treat bacterial infections. Understanding the structure and mechanism of phages can help researchers develop more effective and efficient phage therapies against resistant bacterial infections. The unique features of the Rapunzel bacteriophage make it an interesting subject for further research into the potential applications of bacteriophages in medicine and biotechnology.