.png)
Recent News 43 : How scientists spy on bacteriophages inside your belly
How scientists spy on bacteriophages inside your belly
Just like humans can catch viruses and get sick, bacteria can also get sick from viruses called phages (short for bacteriophages). These phages infect only bacteria, turning them into virus factories. In the end, the phages burst the bacteria open from the inside, releasing more viruses into the environment and killing their bacterial host.
Because they naturally hunt down and destroy bacteria, phages are being explored as treatments for infections (See article about phage therapy), especially those caused by antibiotic-resistant bacteria that can send us to the hospital. Another exciting area of research is using phages to engineer the gut microbiome, which is the community of microorganisms, mostly bacteria, living in our large intestine. A healthy gut microbiome supports a strong immune system and has even been linked to mental well-being. On the flip side, a disrupted microbiome has been connected to diseases, such as obesity and colon cancer. Because phages are specific to certain bacteria, they could become a powerful tool to precisely remove unwanted bacteria from the gut microbiome without harming beneficial ones. However, studying how phages multiply and spread within microbial communities is difficult with current methods, especially in a complex environment. To help solve this problem, scientists developed a new fluorescence-based method called Phollow. This innovative approach enables the researchers to watch phages in real time, inside living animals, to see how they spread and replicate.
Making phages glow to follow their path
To track these tiny viruses, the researchers came up with an ingenious strategy to make the phages glow in different colors. They modified the phage capsid, which is the shell protecting the viral DNA, to carry a small tag called SpyTag. Meanwhile, the bacteria were engineered to produce a matching protein called SpyCatcher, fused to a fluorescent protein.
When the phage produces its capsid inside the infected bacterium, the SpyCatcher protein binds to the tag and makes the virus glow with a specific color. When the bacterial cell bursts, the glowing phages are released into their surroundings. Even more impressive, the scientists gave different SpyCatcher-fluorescent protein combinations to different bacteria. This means that phages changed color after infecting a new bacterium. By following these color shifts through microscopy, scientists could track how phages moved from one bacterium to another, thus showing exactly where they had travelled.
Phollow was then used to observe how P2 phages replicate inside Escherichia coli. P2 phages are prophages, meaning they stay hidden inside the bacterial genome until they are triggered to become active in a process called induction. After induction, the phage begins to make new viruses inside the bacterium. Thanks to Phollow, researchers were able to capture every step of this cycle, from induction to the assembly of new viruses, the bursting of the bacterial cell, and the dispersal of phages into the environment. Interestingly, the study revealed novel features of P2 phages, that tend to form large clusters inside the bacterium, which then break apart into single viruses when the bacterium is killed.
Watching viral outbreaks in transparent fish
To monitor how phages replicate and spread inside a living vertebrate (a more complex living organism than bacteria), the researchers turned to zebrafish. Zebrafish are widely used in medical research because they share many genetic similarities with humans. Even more helpful for this kind of study, zebrafish larvae are naturally transparent, which makes it possible for scientists to directly observe their organs in real time.
In this experiment, germ-free zebrafish were colonized with Phollow-tagged bacteria, either E. coli or Plesiomonas. These bacteria carried engineered P2 prophages so that phage replication could be tracked with Phollow. After the prophages were induced and started making new viruses, researchers observed rapid and short-lived phage outbreaks all along the gut, with the viruses being expelled into the surrounding water.
Interestingly, while phages from E. coli stayed mostly inside the gut, phages from Plesiomonas were seen spreading beyond the gut into other organs, including the liver and brain. The live imaging showed not only the bursting of bacteria to release the phages but also secondary infections, where phages infected new bacterial hosts in the gut. They also observed that the infection and bursting of bacteria by phages could reorganize the whole bacterial community in the gut.
To sum up, this study shows how Phollow, a fluorescent tagging system, makes it possible to track phages in real time inside living animals. By revealing how phages spread and interact with gut bacteria, this work opens new possibilities for microbiome engineering and the use of phages to fight harmful bacteria.
Comments
Post a Comment