Paolo Rossi Castelli 4 March 2021 5 min read

140,000 different types of viruses in our gut

Surprising study published in the journal Cell. Many of these viruses infect gut bacteria. The majority, however, do not create problems for the body.


There are at least 140,000 different types of viruses in the gut, more than half of which have just been discovered and that are a mystery to us.

This is the surprising result of a study published in the scientific journal Cell by researchers from the UK’s Wellcome Sanger Institute and the European Molecular Biology Research Laboratory (EMBL) in Heidelberg (Germany).

The researchers used a special technique to “read” the genetic code, called metagenomics. They thoroughly analysed the content of over 28,000 gut microbiomes, collected from different parts of the world. The microbiome, as we recall, is the set of genetic heritage possessed by microbiota, i.e. by all the microorganisms – bacteria, viruses and others – that live in our gut without damaging it.

The result was the discovery of over 140,000 different gut viruses, the vast majority of which are DNA viruses (and not RNA viruses, such as coronaviruses or Zika). The researchers also identified 280 specific groups of viruses from geographical areas across five continents. New studies will now be needed to understand how these viruses affect human health.

Normally, microbiota live in harmony with our bodies and perform important functions. In certain cases, though, imbalances occur, which can contribute to the onset of diseases and other complex conditions, such as inflammatory bowel disease, allergies and obesity.

Bacteriophages Gut Viruses: what they are

However, relatively little is known about these mechanisms. In particular, the effects of viruses called bacteriophages (or, more simply, phages) that infect bacteria in the gut are not well understood. Bacteriophages are actually very numerous and make up the majority of the 140,000 viruses that scientists have catalogued. The function of other viruses, on the other hand, still needs to be deciphered. But, since the samples examined in the study came mainly from healthy people, it is likely that they are harmless “housemates” of the human body, which have reached an advantageous compromise with their host.

“It’s important to remember that not all viruses are harmful, but represent an integral component of the gut ecosystem,” explains Alexandre Almeida, co-author of the study.

We must also consider that bacteriophage viruses contribute significantly to the natural selection (evolution) of bacteria living in our gut.

Within the 140,000 viruses, the scientists also identified a new clade, i.e. a group of bacteriophage viruses that share a common ancestor. It has been named Gubaphage and is the second most prevalent virus clade in the human gut, following another clade discovered in 2014, and named crAssphage, with functions that are still unknown.

The viral sequences identified by the researchers (thanks also to artificial intelligence) have been entered in a large archive called The Gut Phage Database. It is expected to become very useful in the coming years, in order to avoid the duplication of the results of research undertaken at international level and to compare what is to be discovered in further investigations. In addition to increasing fundamental knowledge that is clearly only in its infancy, the study of these viruses could also lead to the discovery of therapies to rebalance our microbiota, if necessary.


Paolo Rossi Castelli

Journalist since 1983, Paolo has been dealing with scientific divulgation for years, especially in the fields of medicine and biology. He is the creator of Sportello Cancro, the site created by on oncology in collaboration with the Umberto Veronesi Foundation. He collaborated with the pages of the Science of Corriere della Sera for several years. He is the founder and director of PRC-Comunicare la scienza.