The Gut Virome and its Implications in Health

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It is no longer a secret that gut microbiota–the trillions of microorganisms residing within the digestive tract–are vital to human health in terms of cognition, digestion, and immunity. While bacteria are the most-studied microbes within this ecosystem, increasing evidence suggests that the viruses in the gut microbiome may be a “missing link” between gut bacteria and host health. These viruses make up the gut virome, and number anywhere from hundreds of millions to billions of viral particles per gram of stool.

“…significant differences in their function, structure, and interactions”

You may be wondering, what is the difference between bacteria and viruses? Both are microorganisms that can be beneficial or harmful to humans and other hosts, but they have significant differences in their function, structure, and interactions. In contrast to bacteria, which are single-celled living organisms, viruses are not considered living-entities because they cannot reproduce independently nor carry out metabolic processes (including growth and reproduction). Further, they are much smaller than bacteria, consisting of just genetic material (either DNA or RNA) enclosed by a protein coat called a capsid and/or an outer fatty membrane. In other words, viruses are simply pieces of DNA or RNA that cannot do anything on their own, so they need to hijack a living cell (such as a human cell or bacterial cell) in order to survive and reproduce. Once inside, viruses replicate by inserting their genetic material into the host cell’s DNA or RNA and hijacking cellular machinery. Subsequently, the phage can lyse (burst) the cell and release new phage particles into the environment, or the phage can remain dormant with its genetic material integrated into the bacterial genome. When lysis occurs in human cells, it causes symptoms that can manifest as COVID-19 or Influenza.

“…phages influence the gut microbiome by preying on specific bacterial species…preventing any single species from dominating the community.”

The human gut contains a vast array of viruses, but the most abundant are bacteriophages, which are viruses that infect bacterial host cells (rather than our human cells). These bacteriophages, or phages for short, make up 90% of the virome, playing a crucial role in modulating bacterial community structure and function in the gut microbiome. Specifically, phages shape the bacterial community through predation and horizontal gene transfer. In summary, phages influence the gut microbiome by preying on specific bacterial species, thereby regulating bacterial population dynamics and preventing any single species from dominating the community. This predation, done through bacterial cell lysis, helps maintain a balanced and diverse bacterial ecosystem, which is essential for gut health and overall well-being. Additionally, phages facilitate horizontal gene transfer by injecting genetic material into their bacterial hosts. This process can lead to the spread of beneficial genes, such as metabolic capabilities, but it can also lead to the spread of antibiotic resistance across different bacterial species. Horizontal gene transfer enhances bacterial adaptability and resilience, contributing to the functional diversity and stability of the gut microbiome.

“…bacteriophages play a vital role in maintaining the intricate balance of the gut ecosystem and promoting host health.”

Through these interactions, phages indirectly affect various aspects of human health, including digestion, immune function, and protection against pathogenic bacteria. By modulating the composition and functionality of the gut microbiota, bacteriophages play a vital role in maintaining the intricate balance of the gut ecosystem and promoting host health.

Due to their ability to influence the balance and activity of bacteria in the gut, phages are being explored as potential treatments for disease states in which gut bacteria are known to play a role. One of the main advantages of using phages as treatment is that they specifically target bacteria and do not affect human cells, which helps reduce side effects. As research continues to uncover the complexities of the gut virome, phage therapy may become a cornerstone in the treatment of bacterial infections and the maintenance of gut health, paving the way for innovative approaches to improving human health.

Madelaine Leitman Madelaine is an undergraduate student at UCLA, with a major in Computational and Systems Biology. Her passion for her ongoing research at the Goodman-Luskin Microbiome Center is fueled by her strong belief that the brain gut microbiome system plays a crucial role in overall wellbeing and health.

This article was reviewed and approved by Emeran Mayer, MD