Bacteriophages may influence the capacity to learn and remember information.

The gut microbiome plays many roles in human physiology, including aspects of brain and neurological health. Because the overall microbial makeup of the microbiome stabilizes around the age of three years, reconfiguring an unfavorable balance with dietary measures or via fecal microbial transplantation has shown limited success. In recent years, scientists have turned to bacteriophages as a possible means of restoring imbalances. Interestingly, bacteriophages may serve other purposes, as demonstrated in findings from a recent study showing that bacteriophages may influence an animal’s ability to learn and remember information.

Bacteriophages (often referred to simply as “phages”) are viruses that infect bacteria. They are abundant in the human gut and exert disparate effects on human health, as seen in their potential roles in resolving bacterial infections and in the pathogenesis of Parkinson’s disease. Bacteriophages are species-specific and typically only infect a single bacterial species or even specific strains within a species. The dominant bacteriophages in the human gut are those of the Caudovirales and Microviridae families.

The study involved more than 1,000 adult participants enrolled in the Ageing Imagenoma Project, an ongoing study of aging patterns among healthy adults (50 years and older) living in Girona, Italy. Participants completed food questionnaires and underwent a battery of cognitive tests, with special emphasis on executive function, one of the key domains of cognitive function.

Investigators collected fecal samples from the participants and measured the viral species present. Interestingly, participants who consumed higher quantities of dairy products tended to have more Caudovirales bacteriophages in their guts. The researchers transplanted fecal samples from the participants into the guts of mice and performed cognitive tests on the mice. Mice that received fecal transplants from participants with more Caudovirales viruses performed better on the cognitive tests than mice that received transplants with fewer Caudovirales.

Next, they fed fruit flies either ordinary whey powder (a dairy product that contains bacteriophages) or sterilized, virus-free whey powder. Then they duplicated the experiment using isolated bacteriophages. In both scenarios, production of genes in the flies' brains that are associated with memory increased.

These findings suggest that bacteriophages, especially those of the Caudovirales family, influence aspects of cognitive function and underscore the potential for capitalizing on the beneficial roles of viral species in the human gut. Learn more about bacteriophages in this interview featuring gut microbiome expert Dr. Eran Elinav.

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