Bacteriophages, viruses that infect and replicate within bacteria, are being rebranded. Once tolerated as harmless inhabitants in the jungle of microorganisms that thrive in human mucous, bacteriophages are emerging in new research as the first responders of a healthy immune system. Forest Rohwer, professor of biology at San Diego State University, told a symposium at ASCB 2015 last December that bacteriophages help humans and many other organisms fight off invading bacteria by using mucosal surfaces as viral stalking grounds. Bacteriophages, Rohwer said, are terrific virus hunters.
“We’ve characterized a new immune system in everything that has a mucous layer, from humans to corals,” Rohwer said in an interview after his talk. Rohwer and SDSU colleagues first published their discovery in 2013 in PNAS that bacteriophages act as an innate immune system in eukaryotic organisms. Since then, the Rohwer lab has learned that phages that bind mucus have a characteristic hunting pattern that increases their chances of bagging bacteria. This supports the idea that phages on mucosal surfaces can act as an immune system.
“What’s happening is that the phages are sticking to mucous, and when the bacteria come in to attack the tissue layer, the phage kills them off. The phages have specific domains to hold onto the mucous,” Rohwer explained. His lab’s latest data show that there is an advantage for the phages sticking in mucous. The mucous-embedded phages come in contact with potential bacterial hosts more often than those that are free moving by Brownian motion, thus they become better “hunters.” This search strategy is particularly effective at the low bacterial concentrations found deep within mucous layers, Rohwer said.
Rohwer, an Idaho native, studied marine biology as an undergrad, switched to immunology for his PhD, and then went on to study coral microbes. For a scientist with these diverse interests, there could be no better place than San Diego. Now his 25-member lab pursues projects in coral microbial ecology, mucous-associated bacteria and phages, microbial and viral communities in cystic fibrosis, and cnidarian (e.g., jellyfish) immunity.
His ASCB talk was a fitting end to a big year for Rowher, since 2015 was the centennial of the discovery of bacteriophages. Rohwer pulled out all stops and even managed to get himself interviewed about phages by The New Yorker. To mark the centennial, Rowher and three colleagues self-published Life in a Phage World, a 404-page illustrated field guide to phages, now available for free download on his website. The beautiful monochrome watercolor illustrations alone make it worth reading. “It features stories of how they hunt, and do all of their functions. Because even though they’re one of the most diverse and abundant biologics, people don’t know much about them,” Rohwer said.
About the Author:
Christina Szalinski is a science writer with a PhD in Cell Biology from the University of Pittsburgh.