Gut bacteria don’t just live in the intestine — they help run it from birth
The importance of gut bacteria in early life is well established. But how the microbial residents of the intestine contribute to gut movement itself — the muscular contractions that push food through…
Scientists publishing in Science found that a signaling molecule called IL-22 — a cytokine typically associated with immune defense and gut wall protection — plays a key role in early gut development. IL-22 is secreted by enteroendocrine cells, specialized cells in the gut lining that can release both hormones and immune signals. In zebrafish larvae, this IL-22 stimulates gut motility — the rhythmic contractions of the intestinal wall — but only when the right bacteria are present.
Zebrafish larvae are a well-established model for studying early gut development because their transparent bodies allow direct microscopic observation in a living animal. The researchers compared larvae with a normal gut microbiota to germ-free larvae — animals raised without any bacteria at all. In the germ-free group, normal gut motility was impaired even when IL-22 was available. The microbiota turned out to be necessary for IL-22 to exert its effect on the intestinal muscle.
A newly discovered three-way axis
Enteroendocrine cells have become a focus of intense research in recent years. Long considered simply as producers of digestive hormones — substances that signal satiety or stimulate the pancreas — they have more recently been shown to communicate directly with the nervous system. This study adds another layer: they also use immune signals to regulate gut movement, and that regulation depends on the microbial environment.
The finding points to a hormone-immune-microbiome axis that is established very early in life. That has implications for understanding gut problems in premature infants, in children whose microbiome has been disrupted by antibiotics, and potentially in adults with functional gut disorders like irritable bowel syndrome — a condition that, notably, is often reported to follow gut infections or antibiotic treatment.
A thread that connects to aging
There is a direct thread to longevity here. The gut microbiome shifts substantially with age, and impaired gut motility is among the most common complaints in older adults. If IL-22 and the microbiota cooperate to regulate intestinal movement, the documented decline in certain bacterial species in older age could be contributing to reduced motility in ways not previously understood. Whether this mechanism operates similarly in humans remains to be studied — and it is a question worth asking.