Irvine, Calif., April 18, 2025 — In a world where gut health is increasingly linked to everything from mental well-being to chronic disease, scientists have just taken a leap forward in understanding one of the microbiome’s most elusive players: viruses that infect bacteria, known as phages. Researchers at the Charlie Dunlop School of Biological Sciences at UC Irvine have developed a powerful new tool, called Phollow, that lets scientists watch viral activity in the gut microbiome of living animals with unprecedented precision — down to a single viral particle.
Led by Assistant Professor Travis Wiles, the study was published in Nature Microbiology and offers a window into how these nanoscopic predators spread, replicate and shape the microbial ecosystems inside our bodies. Understanding how phages behave could one day lead to revolutionary ways to fine-tune the microbiome for better health.
For years, scientists have suspected that phages play a key role in keeping gut bacteria in balance — eliminating harmful microbes while enabling beneficial ones to thrive. But directly observing this process has been nearly impossible due to the small size and ephemeral activity of phages. The Phollow system changes that.
“With Phollow, we are able to watch phage outbreaks for the first time within the gut microbiome of a living animal,” said Wiles, the study’s senior author. “Directly observing how phages replicate and spread in microbial communities has the potential to yield clues to harnessing them for microbiome engineering and improving health.”
To make these invisible players visible, the team used zebrafish. By tagging phages with fluorescent markers, researchers tracked their every move. They found that antibiotics can trigger sudden “viral blooms,” where phages rapidly multiply and spread, dramatically altering a zebrafish’s gut microbial landscape in just hours.
“Illuminating phages with fluorescent proteins was somewhat straightforward but only the first step,” explained postdoctoral scholar Liz Ortiz, the study’s first author. “The nanoscopic size and dynamic nature of phages made it challenging to know where and when to find them within macroscopic animal hosts. We were able to overcome this challenge using zebrafish, which are small and transparent and thus made it possible to follow phage virions across the entire body.”
What they saw surprised them. In some cases, viral particles didn’t just stay in the gut — they appeared in the liver and even the brain, raising intriguing questions about how these microbial agents might interact with the body far beyond the digestive system.
The implications of this work go far beyond basic science. As scientists explore how to design personalized probiotics and develop phage therapies to combat drug-resistant bacteria, understanding how phages spread and interact with different hosts is essential. Phollow could become an essential tool for building that knowledge.
“The next major step is to understand how phage outbreaks shape health and disease,” said Wiles. “This will involve using Phollow to begin studying the immense diversity of uncharacterized phages that make up the intestinal virome.”
As the world begins to grapple with the promise and peril of manipulating the microbiome, tools like Phollow bring clarity to a once-invisible frontier. UC Irvine’s research points toward a future where targeted, phage-based therapies could enhance gut health, fight infections and perhaps even prevent disease — one viral particle at a time.
About the University of California, Irvine Charlie Dunlop School of Biological Sciences:
Recognized for its pioneering research and academic excellence, the Charlie Dunlop School of Biological Sciences plays a crucial role in the university’s status among the nation’s top 10 public universities, as ranked by U.S. News & World Report. It offers a broad spectrum of degree programs in the biological sciences, fostering innovation and preparing students for leadership in research, education, medicine and industry. Nestled in a globally acclaimed and economically vibrant community, the school contributes to the university’s impact as Orange County’s largest employer and a significant economic contributor. Through its commitment to exploring life’s complexities, the Dunlop School embodies the UC Irvine legacy of innovation and societal impact. For more on the Charlie Dunlop School of Biological Sciences, visit https://www.bio.uci.edu/.