Could gut microbiota be taking the limelight from viruses in digestive health research? A new international study looking into the stools of 1-year-old babies threats to do so. Or at least, to make them share the role. For five years, a team of scientists has analyzed diaper samples of 647 healthy Danish children as part of a long-term asthma and chronic inflammatory disease project. Unexpectedly, they found 10,000 virus species, 10 times the number of bacterial species in the same children, most of them yet unknown and undescribed, that could act as true allies in adult health.

Of the viruses discovered, 90% are bacteriophages, i.e., they do not infect human cells or cause diseases in children, but attack gut bacteria. In this sense, the main hypothesis for the time being is that in doing so they help shaping bacteria’s competitive abilities and balance populations within the gut microbiome. That is why scientists think that those viruses could play an important role in protecting children from chronic diseases.

“From early childhood, healthy children tumble around with a vast diversity of gut viruses, which probably have a major impact on whether they develop various diseases later on in life”, stated in a press release University of Copenhagen professor Dennis Sandris Nielsen of the Department of Food Science, senior author of the research paper published in Nature Microbiology.

Human gut is home to a myriad of microorganisms, such as bacteria, or viruses, and there is solid scientific evidence on the role those microbes play in physical and mental health. In the last decade, a growing number of studies have unveiled how crucial it is for all those microorganisms, and especially bacteria, to establish and develop well in children’s intestines during early life, and its impact on health later on in life.

Nevertheless, the findings of this new study point out that viruses also play a role on health and disease. “Viruses and bacteria and the immune system most likely interact and affect each other in some type of balance,” pointed out Nielsen who highlighted “Any imbalance in this relationship most likely increases the risk of chronic disease.”

 

A changing virome throughout life

In the same way that the composition of gut microbiota is unique for each of us, so is the gut virome, the set of viruses living in our colon. Also, it is stable over time in adults, which means that we will carry the same combination of viruses as we age. That is not applicable to children, scientists have discovered that an early virome is quite different from an adult virome, and it needs about 2 years to stabilize.

So, babies are born with a kit of bacteriophages that do not persist over time but these get replaced by adult bacteriophages. The families of viruses in infant and adult guts are linked to the bacteria they infect. For instance, viruses that attack Bifidobacterium species, a type of microorganism that is crucial for infant health, are found in early life, but decrease in number and eventually disappear as we age.

On the other hand, the most common viruses in adult guts are not present in babies, which means the infants acquire them as they age. A story similar to that of bacteria.

Scientists think that those bacteriophages are allies. According to Nielsen, “some can provide their host bacteria with properties that make it more competitive by integrating its own genome into the genome of the bacteria.” In doing so, a bacteriophage can, for instance, increase bacterial ability to absorb carbohydrates and metabolize more things. Also, viruses keep bacterial populations in check, a bit like “lion and gazelle populations in the savannah.”

The authors of the research defend that their findings have shed light to learn more about the role of bacteria and viruses in a well-trained immune system. “It can hopefully lead us to being able to prevent many of the chronic diseases that affect so many people today,” said Shiraz Shah, first author of the paper.

 

 

Reference:

Shah S.A., Deng L., et al. Expanding known viral diversity in the healthy infant gut. Nat Microbiol 2023 doi:10.1038/s41564-023-01345-7