The gut microbiome is typically associated with bacteria, but did you know it also contains a wide variety of viruses? These viruses play crucial roles in the digestive system microbiome and are significant in both health and disease.

The Gut Microbiota

The gut microbiota is a diverse ecosystem housing bacteria, fungi, archaea, and viruses, all of which have important physiological and health effects. The microbiome is so vital that scientists consider it a functional ‘organ.’ While most research has focused on the bacterial component (the bacteriome), our gut also hosts approximately 108-1010 virus-like particles per gram of intestinal content[1], making up a significant portion of the microbial population.

Our viral community consists mostly of prokaryotic viruses that infect bacteria (bacteriophages) and, to a lesser extent, viruses that infect other microorganisms and human cells, such as eukaryotic viruses, archaeal viruses, and plant viruses[2].

The Gut Virome from Birth to Adulthood

The gut virome, like the bacteriome, changes over time. The initial period of microbial acquisition is thought to be crucial for healthy development. When babies are born, early stools contain very few, if any, detectable viral-like particles. Phages are the first viruses to appear, and as the baby grows, the composition of the phage community changes, possibly in response to shifts in the gut bacteriome[3].

Diet influences which viruses are present in our gut. For instance, studies have shown that breastfed infants have fewer eukaryotic viruses compared to formula-fed infants in their gut; this is likely due to protective immune factors passed from the mother to the infant during feeding. The mode of birth, whether vaginal delivery or Caesarean section, might also impact the development of the virome[3][4].

As we age, our viral community stabilises but remains unique to everyone. Factors such as age, diet, sex, geographic location, ethnicity, and stress levels can influence virome structure[5].

The Gut Virome in Heath and Disease

The scientific community has established the symbiotic contribution of gut bacteria; however, the role of gut viruses is still unclear. Scientists have learned that these viruses play a significant role in regulating the development and responses of the immune system. For instance, a study on antibiotic-treated mice with a single eukaryotic virus demonstrated that the virus protected the mice against intestinal injury and bacterial infection. This highlights the ability of eukaryotic viruses to shape mucosal immunity and support intestinal homeostasis[6].

The gut virome can regulate the immune system both directly and indirectly. Phages, for instance, can travel the intestinal lining to interact directly with immune cells. Additionally, they influence the release of immunomodulatory compounds (such as bile salts), by altering the gut bacteriome composition and metabolic output[7].

The virome community goes beyond the metabolic and immune system roles. A recent study found that people with higher concentrations of Caudovirales phages in their guts (a diverse and abundant group of gut phages) performed better in executive processing and verbal memory than those with higher levels of Microviridae (another common group of gut phages). The researchers suggest that the ratio of these two phages could alter host bacterial metabolism and influence cognitive function through the gut-brain axis[8].

Alternatively, perturbations in the intestinal virome could lead to the development of several diseases, such as inflammatory bowel disease (IBD), type 1 and 2 diabetes, obesity, and colorectal cancer. The hypothesis is that perturbations in the gut virome lead to altered interactions with the immune system, further contributing to inflammation and pathogenesis[9].

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Please note that BioLabTests does not test human, animal or food samples and we do not test for viruses.