Scientists have identified a previously uncultured microbe that is present in the guts of healthy people across the globe.
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Does the gut microbiome still hold secrets?
The simple answer is yes, even though it might feel like scientists know all there is to know about the magnificent ecosystem that lines the gastrointestinal tract. The critical answer is they don’t. We know it is a bustling ecosystem of trillions of microorganisms that influence everything from digestion to immunity and even mental health [1]. Still, researchers are only just scratching the surface of what really lives inside us and what goes on.
A new global study, analyzing 11,115 gut microbiome samples, has uncovered something remarkable. A previously unknown group of bacteria that consistently appears in healthy individuals worldwide has been discovered, and, what's more, it’s never been grown in a lab.
The discovery sheds more light on what scientists are calling the “uncultured microbiome” and could reshape how we think about gut health, nutrition, and future therapies.
What is the “uncultured gut microbiome”?
The uncultured microbiome represents the 60% of the species in the gut which have not yet been cultured and analysed [2]. These include archaea, bacteria, and fungi that cannot be grown in the lab using standard techniques.
Why can’t many gut bacteria be studied in the lab?
Many species in the gut, approximately 50%, cannot be studied in the lab because they are highly specialized to the unique, anaerobic colonic environment, making them difficult or practically impossible to culture using standard techniques [3].
These microbes may rely on highly specific environmental conditions or interactions with other bacteria that are difficult to replicate outside the human gut. As a result, they have remained largely invisible to researchers.
These microbes may rely on highly specific environmental conditions or interactions with other bacteria that are difficult to replicate outside the human gut. As a result, they have remained largely invisible to researchers.
How scientists study hidden microbes
To overcome this challenge and delve deeper into what’s really going on inside the human gut, scientists are employing a technique called metagenomics.
Rather than trying to grow microbes on a petri dish, metagenomics enables scientists to study the genetic material from environmental or clinical samples [4]. In this case, they study the DNA/RNA extracted from human faeces to unlock the secrets of the gut microbiome.
Metagenomics essentially enables researchers to identify microbes by their DNA and create a “genetic fingerprint” of the gut microbiome, allowing the detection of previously unknown organisms and exploration of their associations with health and disease [5].
Inside the study: Analyzing over 11,000 global gut microbiomes
The study by da Silva and colleagues, published in Cell Host & Microbe on 11 March 2026 analyzed 11,115 gut microbiome samples from individuals across 39 countries, primarily in Europe, Asia, and North America. The large-scale dataset allowed researchers to capture a diverse picture of the human microbiome across different populations, diets, and lifestyles.
Figure 1. The study analyzed 11,115 gut metagenomes and identified 4,612 bacterial species, of which 3,067 are uncultured. The CAG-170 group were shown to have the strongest association with a healthy gut microbiome.
Comparing healthy vs diseased microbiomes
One of the key factors in this study was the inclusion of both healthy and diseased microbiomes. The study included people with 13 different non-communicable diseases, including:
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Multiple sclerosis
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Colorectal cancer
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Crohn’s disease
By comparing the composition of “healthy” gut microbiomes with those of people living with chronic conditions, the scientists aimed to identify distinct microbial patterns, also known as “signatures,” linked to health.
The study identified 317 microbial species associated with either health or disease. Notably, many of the bacteria linked to positive health outcomes belonged to the uncultured microbiome.
This suggests that some of the most important players in gut health may have been overlooked simply because they cannot yet be grown in the lab.
Meet CAG-170: The Mysterious Bacteria Linked to Good Health
Among all the microbes identified in the study, one group stood out: CAG-170. This little-known group of bacteria was consistently identified in healthy people throughout the world. The interesting thing about CAG-170 is that researchers know it only by its genetic signature because it’s never been successfully grown in a lab and has evaded significant study, meaning we know very little about it.
Back in 2021, one of the researchers involved in this study, Alexandre Almeida, published a work that created a comprehensive reference catalogue of the genomes of the human gut microbiome, called the “Unified Human Gastrointestinal Genome catalogue.” Included were 4600 bacterial species, including more than 3000 that had not been identified in the gut before - the uncultured microbiome. The catalogue provided ‘reference genomes’ that scientists could use as a basis for research on other gut microbiome samples. CAG-170 was included in this catalogue [6].
What does the presence of CAG-170 in the gut mean?
When comparing the 11,115 samples collected with the Unified Human Gastrointestinal Genome catalogue, CAG-170 was consistently found in the guts of healthy people worldwide. This is similar to other studies in which CAG-170 has been found in non-obese individuals [7] and is associated with better cardiometabolic health [8].
Further analysis of over 6,000 healthy people demonstrated that the CAG-170 group was most consistently linked to a healthy gut microbiome. While a separate third analysis showed that reduced levels of CAG-170 were linked with a higher chance of dysbiosis or an imbalanced gut microbiome.
Figure 2. Higher levels of CAG-170 are linked to a healthier gut. (A) This graph shows that as gut imbalance (also known as dysbiosis) increases, CAG-170 levels decrease. In other words, people with a more disrupted gut microbiome tend to have lower amounts of this bacterium. The blue line represents the overall trend, and the shaded area indicates the confidence level for this result.
(B) This box plot compares people with low dysbiosis (healthier gut) and high dysbiosis (more imbalance). Those with a healthier gut had noticeably higher levels of CAG-170. The middle line in each box shows the average value, while the boxes and lines illustrate how much the values vary between individuals.
Note: Samples where CAG-170 was completely absent were not included in these visualisations.
This is important because dysbiosis is associated with numerous chronic conditions [9], including many included in this study. Dysbiosis triggers low-grade inflammation, weakens the intestinal barrier, leading to a phenomenon called leaky gut, and disrupts metabolic functions. Characterized by a loss of beneficial microbes and an increased abundance of pathogens, dysbiosis drives illnesses, such as:
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obesity
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diabetes
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heart disease
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autoimmune conditions [10]
What does CAG-170 do in the gut?
The researchers found that CAG-170 appears to have some useful functions within the gut, including stabilizing the ecosystem and producing vitamins.
Supporting the gut ecosystem
Although researchers have not yet cultured CAG-170, genomic analysis provides clues about its function.
It appears to play a role in maintaining balance within the gut ecosystem, potentially acting as a “keystone species” or a microbe that supports the stability and diversity of the wider microbiome.
This may involve interactions with other bacteria, including cross-feeding mechanisms where microbes share nutrients and metabolic byproducts.
CAG-170 and vitamin B12
A key biological feature of CAG-170 unveiled in this study was its enrichment of genes linked to vitamin B12 synthesis. Vitamin B12 is important for the production of short-chain fatty acids [11] and amino acid metabolism. This discovery led the researchers to conclude that CAG-170’s increased capacity to produce vitamin B12 could be the key to its health benefits. It’s likely that the vitamin B12 produced by CAG-170 benefits many other gut species rather than supporting the host directly.
What does this study mean for the future?
It’s estimated that more than 5,000 different microbial species are present in the human gut [12], and yet many of us still take the same probiotics, usually belonging to the Bifidobacteria or Lactobacillus genera (and maybe a couple of others like Akkermansia, etc.). With the discovery of new bacterial groups, such as CAG-170, identifying and developing probiotics that support these groups could offer a wide range of benefits.
For example, we’ve learned from this study that CAG-170 is far less abundant in diseased microbiomes than in healthy ones, so in the future, probiotics could be a promising therapeutic approach to “correcting” unhealthy microbiomes.
There’s also potential for these newly discovered groups to serve as biomarkers for health, particularly in relation to the gut. In the future, microbiome testing could measure the presence or abundance of specific microbial groups to provide deeper insights into the host's health status and disease risk.
For now, though, scientists need to work out how to grow and culture these groups to fully harness their therapeutic potential.
Take the next step to support your gut health
Discoveries like CAG-170 highlight that there’s still much to learn about the human gut microbiome, but in the meantime, it’s clear that supporting beneficial bacteria is key to good health. To do that, we must feed them wisely.
A good place to start is a diet that’s rich in a diverse range of fibers that can help nourish and sustain the bacteria that are associated with better health outcomes. Human milk oligosaccharides (HMOs) act as prebiotics, feeding and diversifying your gut microbiota and supporting a more balanced environment. Take a proactive approach to gut health and explore our range of PureHMO® products.
Author details
Written by: Leanne Edermaniger, M.Sc. Leanne is a professional science writer who specializes in human health and enjoys writing about all things related to the gut microbiome. She has written extensively on inflammatory bowel disease, prebiotics, and microbiome research.
Her work focuses on translating complex medical science into evidence-based, practical health guidance.
