An international team of scientists who spent five years studying the stool of 647 Danish babies discovered something surprising.
The diaper samples contained 10 000 species of viruses – ten times the number of bacterial species in the same children. Most viruses have never been described before.
This may alarm many readers. Viruses haven’t exactly had a good reputation in recent years. But what many people don’t realize is that the overwhelming majority of viruses don’t make people sick and does not infect humans or animals.
The viruses in question are bacteriophages. They exclusively infect bacteria and make up a large part of the human microbiome. It is these bacteriophages that researchers have found so abundantly in babies’ poo. In fact, around 90% of the viruses found in Danish baby diapers were these bacteria killers.
The human gut microbiome is a complex collection of microorganisms, including bacteria, archaea, microbial eukaryotes, and viruses. The viral component of the gut microbiome, or virome, is primarily composed of bacteriophages that help maintain a healthy and diverse microbiome.
Atlas
The researchers in this new study – a collaborative team from Denmark, Canada and France – looked at how many of those 10,000 viruses were new and how best to describe all this new viral diversity in an accessible way.
Putting them all on one big table would be pretty boring reading. Instead, they created aatlas of infant gut DNA virus diversity”, where they grouped the viruses into new families and orders of viruses based on the similarity of the genomes to each other. They found 248 families of which only 16 were previously known.
The scientists named the remaining 232 newly identified virus families after children who participated in the study, such as Sylvesterviridae, Rigmorviridae, and Tristanviridae. An interactive version of the atlas is available online.
single viromas
What’s interesting about bacteriophages and other viruses in the gut is that each person has your own unique setalmost no overlap between two different people.
Although each intestinal virome is unique, it is also stable over time in adults, which means that each of us carries the same set of viruses with us as we age. But right after the birth of a baby, this virome is very different from that of an adult and only stabilizes after a few years.
By comparing the approximately 10,000 viruses in this new study to extensive collections of reference viromas from healthy adults, the scientists found that only about 800 of these viruses had been found before.
This means that when babies are born and have the first bacteriophages to colonize their gastrointestinal tract, these “baby bacteriophages” don’t all stay therebut are gradually replaced by “adult bacteriophages”.
This substitution may be partially linked to the bacterial hosts that these bacteriophages infect. For example, Bacteroides, Faecalibacterium and Bifidobacterium were the most prominent hosts predicted for baby bacteriophages.
Bifidobacterium species are very important for infant health, as they help with the digestion of breast milk and therefore are important early in life, but become less abundant as we age. So it makes sense that the viruses that infect Bifidobacterium are found more in babies and less in adults.
On the other hand, the most abundant group of adult intestinal bacteriophages, members of the order Crassvirales, was not as prevalent in baby poowhich means that children acquire these bacteriophages as they age.
With the addition of these 10,000 new virus species and many new families, from just a group of several hundred Danish babies, it’s clear that there’s more we don’t know about the virome. But the scientific community is working on it, one baby poo sample at a time.
