The hidden bacteria you can’t grow in a lab – and why they may matter most for gut health
By Alena Pribyl, Lead Scientist at Microba
More than 60% of the bacterial species in the human gut remain “uncultured” — identified through DNA sequencing but never grown in a laboratory. A large new study published in Cell Host & Microbe (March 2026) asked whether these elusive microbes matter for health. A team from the University of Cambridge analysed over 11,000 stool metagenomes from 39 countries, spanning healthy individuals and patients with 13 non-communicable diseases including inflammatory bowel disease, colorectal cancer, obesity, and Parkinson’s disease.
Although uncultured bacteria accounted for only about 12% of total microbial abundance per sample, they carried nearly as much diagnostic information as the cultured species making up the other 88%. One genus stood out above all others: CAG-170, a little-known member of the Oscillospiraceae family. Across multiple diseases and geographies, CAG-170 was consistently more abundant in healthy people, was the most interconnected genus in ecological networks of healthy microbiomes worldwide, and remained stable over a year-long follow-up period. Functionally, its genome showed an enriched capacity for vitamin B12 production and evidence of cross-feeding — producing metabolites that neighbouring species depend on.
This is observational research, so the link between CAG-170 and health does not yet prove causation, and factors like diet and medication were not consistently controlled for. Still, the scale and global breadth of this analysis make the findings compelling. As culturing techniques advance, genera like CAG-170 are well worth watching — they suggest some of the gut’s most clinically relevant residents may be hiding in the portions we cannot yet grow in a dish.
