A C. elegans worm (black wiggle) prefers a safe meal (E. coli, right) over a toxic one (Staphylococcus saprophyticus, left). Image credit: Yating Liu (CC BY 4.0).
Eating is essential for survival – but not all food is safe. Spoiled or toxic meals can cause illness, so animals must distinguish good food from harmful food. While the brain helps animals smell and taste, it is less clear how the nervous system communicates with the digestive system to prevent harm.
The tiny worm Caenorhabditis elegans (C. elegans) is a powerful model organism in biology because it has a simple nervous system and a transparent body. Living in soil and feeding on bacteria, the worm encounters both harmless and harmful species. One such bacterium, Staphylococcus saprophyticus, is toxic to C. elegans. Previous work showed that worms can avoid poor-quality food, but the mechanisms behind this behavior were unknown.
Liu et al. investigated how C. elegans detects and responds to dangerous food by exposing the worms to S. Saprophyticus for one to four days and by using a combination of genetic and imaging approaches to study the activity of neurons. With this approach, the team identified a pair of neurons in the worm’s head, called AWC neurons, as key “taste sentinels.”
A protein located in these neurons, NSY-1, enabled the worms to recognize S. saprophyticus as a threat. This detection triggered a neural circuit (the AWCOFF state), sending a body-wide signal that shut down the digestive system. Without this protective mechanism governed by the nsy-1 gene, worms continued to digest the toxic bacteria and had a shortened lifespan.
Further experiments revealed that these neural signals also regulated hormone-like peptides and gut-specific genes, fine-tuning digestive activity. Thus, NSY-1 functions as a molecular sensor that links the nervous system to the gut, forming a direct communication line that helps the animal avoid harm.
These findings reveal a fundamental survival mechanism that may represent an ancient system shared across animals, including humans. Understanding this brain–gut crosstalk in worms could provide insights into how the human nervous system defends against foodborne pathogens and toxins and may also illuminate the biological basis of some digestive disorders.
However, further research is needed to determine whether similar signaling pathways exist in mammals. Identifying equivalent molecules in humans could open new avenues for understanding and treating digestive disorders and food-related illnesses.
