The human intestine is normally home to not only bacteria (the microbiome) but also viruses (the virome), primarily bacteriophages. But how they interact with bacteria remains unclear.

Scientists currently know little about the gut microbiome, but even less about the virome. To learn more, researchers from the University of Cork (Ireland) studied* the gut virome of nine people for a year and one person for two years. They found that the human gut is home to many types of bacteriophages, and their composition varies from person to person.

The study resulted in the creation of a database of intestinal bacteriophages, which could significantly advance our understanding of how phages influence human health. The findings demonstrate that, unlike the microbiome, whose composition is largely consistent across individuals, the virome varies significantly. This means that the same bacteria host different bacteriophages in different individuals.

In the study*, stool samples were collected from 10 people—4 men and 6 women—monthly for a year. One woman also received samples at the 19th, 20th, and 26th months of observation. Viral particles were isolated from the samples, and the viral genome sequence was determined. Since 99% of enteric viruses are unknown to science, it is currently impossible to identify them. Therefore, the scientists searched for coding sequences of viral DNA and analyzed the proteins they may encode, as well as their matches to proteins in existing databases. The scientists discovered that the virome contains many virulent bacteriophages—those that require the destruction of the host bacteria to reproduce.

Microbiologists currently know very little about the interactions between bacteriophages and human intestinal bacteria, but studies of the microbiome in health and disease undoubtedly require the virome as well. It would be useful to understand the virome of a healthy person and how it varies depending on lifestyle, location, ethnicity, and so on. Understanding what constitutes normal microbiomes will help us better understand pathological conditions associated with changes in the viral composition of the gut.

* Shkoporov A., Clooney AG, Sutton TDS et al. The human gut virome is highly diverse, stable, and individual specific // Cell Host & Microbe, 2019, 26 (4): P527-541.E5. DOI: https://doi.org/10.1016/j.chom.2019.09.009