Most viruses in the human gut are phages, or bacteriophages, viruses that infect bacteria. Photo by Dr. Graham Beards/Wikimedia Commons
Aug. 24 (UPI) -- Much of the research into the microbial contents of the human digestive tract has focused on bacteria, but there are viruses in the human gut, too.
The virome is the equivalent of the microbiome, and research published Monday in the journal Cell Host and Microbe suggests each human hosts a unique virome in their gut.
Scientists examined data from 32 studies of viruses in the guts of nearly 2,000 individuals from 16 different countries, including both healthy and sick people.
The survey, which relied on machine learning algorithms to identify previously known viruses, found 33,000 different viral populations.
"We were interested in how many types of viruses we could see in the gut, and we determined that by how many types of genomes we could see since we couldn't visually see the viruses," Ann Gregory, who conducted the research while a graduate student at Ohio State University, said in a news release.
The analysis failed to reveal a core community of gut viruses common to all humans, but scientists were able to identify a variety of trends.
In healthy individuals from the Western Hemisphere, virus diversity in the gut increases and decreases over the course of a person's lifespan. From childhood to adulthood, biodiversity increases, before decreasing after age 65. Gut microbiome diversity follows the same pattern.
However, scientists did find a difference between the virome and microbiome in the human gut. Whereas newborns and infants, with undeveloped immune systems, are short on bacterial diversity, the latest research suggests their guts are teeming with viruses.
Researchers found measurable differences in the virus diversity inside the guts of Western and non-Western individuals, as well as differences in the diversity of viruses in the guts of sick and health individuals.
"A general rule of thumb for ecology is that higher diversity leads to a healthier ecosystem," Gregory said. "We know that more diversity of viruses and microbes is usually associated with a healthier individual. And we saw that healthier individuals tend to have a higher diversity of viruses, indicating that these viruses may be potentially doing something positive and having a beneficial role."
The overwhelming majority of viruses found in the gut, 97.7 percent, were phages, the types of viruses that infect bacteria. Most viruses don't cause disease in humans.
Researchers suggest an improved understanding on the human virome could help medical researchers develop new strategies for fighting disease-causing bacteria.
"Phages are part of a vast interconnected network of organisms that live with us and on us, and when broad-spectrum antibiotics are used to fight against infection, they also harm our natural microbiome," said senior study author Matthew Sullivan, who leads a virus research lab at Ohio State. "We are building out a toolkit to scale our understanding and capabilities to use phages to tune disturbed microbiomes back toward a healthy state."
"Importantly, such a therapeutic should impact not only our human microbiome, but also that in other animals, plants and engineered systems to fight pathogens and superbugs," Sullivan said. "They could also provide a foundation for something we might have to consider in the world's oceans to combat climate change."