IBD: the role of gut microbiota viruses
The decrease in bacterial abundance and diversity caused by inflammatory bowel diseases is associated with a significant change in content of bacteria-killing viruses called bacteriophages. Little studied until now, these viruses may play a major role in the development of IBD.
IBDs or chronic inflammatory bowel diseases, particularly Crohn's disease and ulcerative colitis, are a group of chronic illnesses with alternating phases of flares and remission. They are linked to changes in the gut microbiota, combining a decrease in bacterial diversity with a reduction in the abundance of certain species. However, more and more studies support the idea of a simultaneous change in the virus population which is also found in the gut, in the form of an overall change in their diversity and a specific increase in harmful viruses.
Abundance of “killer” viruses
To identify the viruses involved in IBDs, an international team studied the gut microbiota of patients with Crohn's disease or ulcerative colitis during both outbreaks and remission, as well as the microbiota of control subjects. The results show that 70% of control subjects share two major groups of viruses that form a “viral core” which is absent during illness. In its place are a multitude of temperate bacteriophages, fearsome viruses that destroy good bacteria, which may explain the lower bacterial diversity observed in the gut microbiota of patients. The authors also found differences between the two diseases. For example, changes in the viral and bacterial composition of the intestinal microbiota are greater in patients with Crohn's disease; in patients with ulcerative colitis, there are very few changes between flares and remission phases, with no clear explanation as to why this is so.
The joint analysis of bacteria and viruses in the gut microbiota helps us understand the changes associated with inflammatory bowel diseases. This approach may eventually lead to the development of biomarkers that are useful for diagnosis and of new therapeutic strategies.
Clooney A.G. et al. Whole-virome analysis sheds light on viral dark matter in inflammatory bowel disease. Cell Host & Microbe. 2019 ; https://doi.org/10.1016/j.chom.2019.10.009