Researchers use army of organoids to detect distinct mutational signature.

A toxin produced by bacteria found in some probiotics – over-the-counter supplements used to treat conditions including irritable bowel and diarrhoea – has been linked to the development of bowel cancer.

Writing in the journal Nature, researchers led by Hans Clevers at the Hubrecht Institute in Utrecht, The Netherlands, report that a strain of the common gut bacteria E.Coli causes DNA mutations that establish it as a probable cause of the cancer.

The team created a small army of “organoids”, mini-intestines grown from cells that line the colon and rectum, and injected them with two strains of E.Coli.

One strain made colibactin, known as a “genotoxin” for its ability to damage cell DNA. The other was engineered so it couldn’t make colibactin.

The team then analysed the genomes of each mini-intestine, looking for a “signature” mutation in the DNA, a fingerprint similar to the changes that UV light produces in skin cells to cause cancer.

They found it in the form of a handful of alterations to adenine, one of the four bases or “letters” in the genetic code.

“I remember the excitement when the first signatures appeared on the computer screen,” says co-author Axel Rosendahl Huber.

“[T]he patterns were more striking than any signature we had analysed before.”

Read the full story in Cosmos magazine here