The latest from the online journal mBio brings you the genomes of 11 viruses that infect the acne-causing bacterium Propionibacterium acnes and pulls back the curtain on some of the microscopic predator-prey struggles that play out on the surface of human skin. The authors say the results could help pave the way for therapies that use viruses or virus products to treat that vexing teenage skin condition.
Ongoing studies of the human microbiome reveal the human body as complex ecosystem much like plant and animal ecosystems, complete with habitats (the various parts of your body), mutually-beneficial commensal interactions (the bacteria in our gut are essential for nutrient absorption), and predators (microbes that make you sick or those that attack one another). A group of scientists interested in learning more about how these ecosystems work zeroed in on two members of the human microbiome: Propionibacterium acnes, a bacterium that can cause acne; and the viruses that infect those bacteria. Viruses that infect bacteria are called “bacteriophages”, or “phages” for short.
Co-author Graham Hatfull of the University of Pittsburgh says scientists estimate there are about 10^31 phages on the planet, an abundance that presents some tantalizing questions for biologists. “The question arises, what is their diversity? How many different types are there? How do they differ and what evolutionary mechanisms give rise to such diversity?” says Hatfull. Answering these questions can help scientists predict where new viruses will come from and how they emerge to impact human health, issues that have a direct bearing on public health.
In the study in mBio, Hatfull and his colleagues isolated phages and P. acnes bacteria from the clogged pores of human volunteers, then sequenced the phages’ genomes. What they found in those genomes surprised Hatfull, he says. The phages were all remarkably similar, sharing more than 85% of their nucleotide bases (the building blocks of DNA), an unheard of level of similarity among viruses, which usually exhibit a great deal of diversity. Using an electron microscope, the researchers found they all look alike as well: each virus has an isometric head about 50 nm wide and a long flexible tail that’s about 150 nm long, making them look a bit like a lollipop.
“There are two fairly obvious potential directions that could exploit this kind of research,” says Hatfull. “The first is the possibility of using the phages directly as a therapy for acne. Knowing what we now know about these phages and a little about the hosts that they infect helps to provide some of that critical background information for going ahead with that approach,” he continues.
“The second is the opportunity to use phage-derived components for their activities,” Hatfull says. All of the phages carry a gene that makes a protein called endolysin, for instance, an enzyme that is thought to break down bacterial cell wall and pop the cell open to allow the phages replicating inside to escape. Enzymes like this are used in other applications, says Hatfull, raising the question of whether endolysin from these phages might eventually be useful as an anti-acne therapeutic. “This work has given us very useful information about the diversity of that set of enzymes and helps pave the way for thinking about potential applications,” he says.
From here, Hatfull says research with these phages will explore how they might be used therapeutically, but phages like these can also provide useful “tools”, like genes and enzymes, that can be used to manipulate and understand the bacteria they infect. “The information derived from these phages helps contribute toward those kinds of genetic tools,” says Hatfull.