A large global study led by University of Cambridge researchers has identified a “hidden” group of gut bacteria, called CAG-170, that repeatedly appears at higher levels in healthy people than in people with a range of chronic diseases. The researchers say the finding could help scientists measure gut microbiome health and may eventually guide probiotics designed to support and maintain healthy levels of CAG-170.
CAG-170 stands out because most of these bacteria have not been grown in the lab and are mainly known from their genetic fingerprints, which has kept them largely out of traditional microbiome research. In the new work, the team searched for that genetic fingerprint across more than 11,000 gut microbiome samples collected from people in 39 countries.
What the study found
Across the dataset, CAG-170 levels were consistently higher in healthy participants than in people with diseases, including inflammatory bowel disease, obesity, and chronic fatigue syndrome. The research also included samples from people with 13 diseases, and the Cambridge report lists examples such as Crohn’s disease, colorectal cancer, Parkinson’s disease, and multiple sclerosis.
The researchers also examined people with dysbiosis, described as an imbalanced gut microbiome, and found that lower CAG-170 levels were linked with a higher likelihood of dysbiosis. The Cambridge report notes that dysbiosis is linked with many long-term conditions, including irritable bowel syndrome, rheumatoid arthritis, and anxiety and depression.
Why CAG-170 may matter
Genetic analysis suggests CAG-170 bacteria can produce high levels of vitamin B12 and carry enzymes that help break down a wide range of carbohydrates, sugars, and fibres in the gut. The researchers think the vitamin B12 produced by CAG-170 likely supports other gut bacteria rather than directly supporting the human host.
Dr. Alexandre Almeida of the University of Cambridge, who led the work, said CAG-170 bacteria appear to be key players in human health and may help digest major components of food while keeping the wider microbiome “running smoothly.” He also said the team repeatedly saw lower CAG-170 levels in people with diseases when they compared gut microbes across thousands of people in 39 countries and across 13 diseases.
How researchers studied “hidden” microbes
The study builds on earlier work led by Almeida to create a reference catalogue of genomes in the human gut microbiome called the Unified Human Gastrointestinal Genome (UHGG) catalogue, using metagenomics to analyse microbial DNA in gut samples and separate it into genomes of individual species. The Cambridge report says that effort identified over 4,600 bacterial species, including over 3,000 that had not previously been seen in the gut, highlighting the scale of the “hidden microbiome.”
In the new analysis, the team compared gut samples against the UHGG catalogue and found that, among hidden-microbiome groups, CAG-170 was most strongly linked with health in a way that held across countries. In another computational approach, they analysed the gut microbiomes of more than 6,000 healthy people to explore which species might help keep the gut ecosystem stable, and CAG-170 again showed up as most consistently associated with health among hidden-microbiome bacteria.
What this could mean for probiotics
The Cambridge report says the findings raise the possibility that CAG-170 could one day serve as an indicator of gut microbiome health and help guide new probiotics aimed at supporting and maintaining healthy levels of this bacterial group. Almeida also argued that the probiotics industry has largely relied on long-used species and has not “kept up” with newer microbiome research that is identifying additional microbes linked to potential health benefits.
Researchers and industry still face major technical hurdles, because most CAG-170 strains have not been grown in the lab, limiting the ability to test them directly and develop products from them. In an interview-style report, Almeida said only one strain has been successfully grown out of more than 300 strains identified to date, and he described challenges including low levels in the gut, sensitivity to oxygen damage, and possible special nutritional requirements.
That same report adds that CAG-170 lacks the ability to produce arginine, and suggests adding arginine to growth media may help support lab growth. Almeida also said that even with strong associations between CAG-170 and health, any commercial use would require reliable isolation methods, extensive safety testing, and confirmation that introduced CAG-170 can establish itself in the gut.
