An early microbial signal can change what adult fruit flies avoid eating, according to research described in a 2026 PLOS Biology article credited to Kyu-Chan Cho. The experiments were conducted by Milleville and colleagues. Their work traces a path from a bacterial molecule encountered by larvae to an adult feeding response, while leaving open how that early experience survives the dramatic changes of metamorphosis.
The reported effect is called developmental priming: an experience early in life changes a later response. In this case, larvae exposed to uracil, a molecule released by certain bacteria, later avoided food containing peptidoglycan, a common component of bacterial cell walls. Feeding larvae uracil alone was sufficient to produce the adult response; related molecules cytosine and thymine did not.
The researchers also tested strains of the fruit-fly-associated bacterium Erwinia carotovora, also known as Pectobacterium carotovorum. Larvae fed strains capable of releasing uracil developed the avoidance response, while larvae fed strains defective in uracil release did not. These results point to uracil as a cue that starts the process, rather than showing that adult flies simply avoid the same bacteria they encountered as larvae.
The proposed route runs through the gut and sensory system. Uracil caused a temporary rise in reactive oxygen species in the larval intestine, with hydrogen peroxide implicated as an important component. Suppressing this redox response prevented priming. The findings therefore suggest that larval sensory neurons respond to a signal generated by the fly, rather than detecting uracil directly.
The article describes evidence implicating TrpA1-B, an ion-channel form in larval Gr66a-positive sensory neurons near the mouth. Silencing these neurons prevented the later adult avoidance response, and restoring TrpA1-B in the cells rescued priming in animals lacking TrpA1. Calcium imaging also showed that hydrogen peroxide activates the neurons in a TrpA1-dependent way. Together, these results support a chain in which a bacterial molecule triggers a gut redox signal, which activates larval sensory neurons and establishes a change that is expressed later.
That later response depends on a different sensory population. Adult avoidance of peptidoglycan-containing food requires ppk23-positive neurons, while larval Gr66a-positive neurons are needed to establish priming but not to carry out the adult behavior. How information passes between those stages is unknown. The fly’s nervous system is extensively remodeled during metamorphosis, so the lasting effect could involve persistent changes in neural circuits or altered development of adult sensory neurons. The reported work does not resolve which explanation is correct.
The findings add a mechanistic example of how an encounter with a microbe during development can shape later behavior through host signaling and sensory neurons. Fruit flies offer researchers a tractable system for examining those links. The evidence does not establish that early microbial exposure has the same effect in other animals, or that the adult avoidance improves survival, resistance to infection, or reproductive success. Those potential benefits remain to be tested.