Symbiotic microbes adapt to colonize the newborn gut and shape early immune development

The newborn gut undergoes dramatic changes in nutrient availability and immune makeup as it develops after birth.

It has been unclear what mechanisms enable bacteria such as Bacteroides fragilis to become more abundant during this dynamic developmental period.

A new study led by Kyoo Heo, PhD, and supervised by Sungwhan Oh, PhD, both of Mass General Brigham, used genetic screening and mouse models to identify how B. fragilis exploit a membrane glycolipid called BfaGC to colonize the newborn gut.

BfaGC remodeled the cell membrane, allowing these bacteria — which normally live in environments without oxygen— to survive a brief window of oxygen exposure during early life.

The researchers found that this approach was unique to B. fragilis and that other, related gut bacteria relied on a different membrane lipid that supports persistence regardless of age.

In addition, BfaGC also regulated the development of natural killer T cells in the gut, suggesting that specialized microbial molecules can influence host immune maturation.

The same adaptation also supported the expansion of toxin-producing B. fragilis in adult mice, showing that a trait that helps bacteria colonize the gut can have different consequences for the host.

Together, the findings reveal how one microbial molecule connects bacterial survival with immune development and help explain how gut symbionts establish themselves in each new generation.

Published in Cell on September 1, 2026 | Read the paper: “Oxygen-responsive bacterial glycosphingolipid links symbiont fitness and immune development in neonatal host”

Summary reviewed by: Sungwhan Oh, PhD, senior author