Breast Milk Has Hidden Sugars. Now We Know Who Can Open Them.
Breast milk doesn't just feed babies. It also feeds the microbes moving into their newborn guts, including Bifidobacterium species that help shape the gut community a child starts life with.
Some of those sugars are easy to reach. Others are locked away, attached to fragments of protein — food sealed in packaging.
A study published November 2, 2026, in Nature Communications has found an unexpected tool these bacteria use to cut that packaging open.
Meet PNGaseA: The Enzyme Nobody Expected
The molecular scissors have a name: PNGaseA.
Enzymes in this family are normally found doing housekeeping inside the cells of plants, fungi and animals — recycling components, not gathering food. Nobody had linked them to how gut bacteria eat.
A team led by Dr. Lucy Crouch at the University of Birmingham found that a strain of Bifidobacterium bifidum — a species common in breastfed infants' guts, originally isolated from a human infant — carries a PNGaseA of its own.
The enzyme snips sugar chains called N-glycans off short protein fragments, freeing the sugars so the bacteria can feed on them. It strongly prefers these small protein fragments over whole, intact proteins.
The team also captured the first-ever structure of a PNGase enzyme holding one of these sugar-carrying fragments. The images show a flap-like structure the researchers call a "cradle" that closes over the fragment, letting the enzyme read both the sugar and the protein piece it is attached to — which helps explain its pickiness.
Dr. Crouch says the team was surprised to find this enzyme being used by gut bacteria to access milk-derived nutrients. It appears to have been picked up by this bacterial lineage at some point in its history, rather than inherited as standard equipment.
The Catch: Three Facts You Shouldn't Forget
This is where the story needs its feet kept firmly on the ground:
- This was laboratory biochemistry, not a baby study. The team produced the enzyme in the lab, tested it on protein substrates in dishes, and mapped its structure. No infants were involved, and no health outcome was measured.
- The enzyme is rare. Screening B. bifidum genomes, the researchers found this gene in just two strains, in a stretch of DNA that varies a lot between strains. It is not a universal feature of infant gut bacteria.
- Nothing here changes feeding advice. The study explains one small mechanism of how certain bacteria may forage in the infant gut. It does not show the enzyme improves babies' health, and it points to no supplement, product or formula change.
What it does do is fill in a blank space in a basic map: how the first bacteria in a baby's gut find food in the complex chemistry of milk. Basic maps like this are what later, applied research is built on — years later, and only if it holds up.
The Twikup Take
Breast milk turns out to be even more intricately matched to the microbes it feeds than scientists thought — right down to bacteria carrying borrowed molecular scissors for its hardest-to-open sugars.
It's a beautiful piece of basic science. Just remember it's a mechanism found on a lab bench, not a health claim about any baby.
Image: AI-generated illustration.