Summary: When fruit flies are missing essential amino acids, their brains reprogram olfactory genes to sharpen the sense of smell and locate food sources that restore those nutrients. Researchers found two key receptors—Or92a and Ir76a—become more active, increasing sensitivity to odors produced by yeast and bacteria that supply or help produce essential amino acids.
Flies deprived of single essential amino acids were attracted to live yeast and certain bacteria, following odor cues such as diacetyl and phenylethylamine (PEA). These cues point to protein-rich or microbe-rich foods capable of correcting nutritional shortfalls. The work reveals a molecular pathway by which internal nutrient needs reshape sensory perception and drive targeted foraging behavior.
Key Facts
- Genetic reprogramming: Deprivation of essential amino acids triggers transcriptional changes that increase expression of specific olfactory receptors tuned to fermented and bacterial odors.
- Microbial attraction: Hungry flies use smell to find live bacteria that improve nutrient uptake and reproductive fitness.
- Adaptive sensing: Internal nutritional state alters sensory wiring, converting physiological need into precise behavioral search strategies.
Source: Champalimaud Centre for the Unknown
To a fruit fly lacking essential nutrients, smells from fermented foods carry crucial information. Removing a single essential amino acid from a fly’s diet triggers a shift in feeding preferences: the insect begins seeking yeast and bacteria that can supply or help generate the missing amino acids. The new study from the Behaviour and Metabolism Lab at the Champalimaud Centre explains how those internal needs are translated into sensory-driven behavior.
Animals cannot synthesize every amino acid they need; essential amino acids must be obtained from food. Even the loss of a single essential amino acid reshapes metabolism and behavior, increasing drive for protein-rich sources. To understand the neural and molecular basis of this change, researchers analyzed gene expression in fly heads after diets lacking each of the ten essential amino acids, compared with a balanced control.
Although each deprivation produced a distinct transcriptional fingerprint, a shared set of changes emerged. Most notably, two olfactory receptor genes—Or92a and Ir76a—were consistently upregulated, pointing to a common sensory adaptation across different nutrient deficits.
A tale of two receptors
Or92a is sensitive to diacetyl, a volatile compound generated by yeast during fermentation that contributes buttery, popcornt-like aromas in food and drink. Yeast is a primary protein source for flies, containing many essential amino acids, so increased Or92a expression makes biological sense. Flies lacking Or92a could still find yeast but fed on it less, suggesting that this receptor contributes to the perceived palatability—or flavor—of protein sources rather than simple localization.
When the team used a yeast strain that does not produce diacetyl, flies showed reduced feeding, mirroring the effect of removing Or92a. The result underscores the role of smell in shaping food evaluation and feeding decisions.
Detecting bacteria: the role of Ir76a
The second receptor, Ir76a, responds to phenylethylamine (PEA), a compound found in some fermented foods like chocolate and certain cheeses. Rather than being attracted to chocolate itself, the researchers discovered flies were detecting the bacteria—Lactobacillus and Acetobacter—that ferment those foods and produce PEA. These same bacteria are common in the fly microbiome.
Live, metabolically active bacteria activated Ir76a neurons strongly and increased feeding behavior in amino-acid-deprived flies. Heat-killed or otherwise inactivated bacteria failed to trigger the response, indicating flies seek bacteria for their active metabolic contribution. Knocking out Ir76a abolished this attraction, showing that upregulation of the receptor is necessary for bacterial-directed feeding under amino acid scarcity.
Previous studies link feeding on specific bacteria to improved egg production and enhanced amino acid availability in nutrient-limited flies. The current findings add a mechanistic layer: the fly brain increases expression of bacterial-sensing receptors to guide behavior toward microbial allies that can mitigate amino acid deficits.
Broader implications
This work illustrates a general biological principle: internal physiological states can reconfigure sensory systems to improve survival. While hunger and appetite have long been known to influence perception, the study demonstrates transcriptional reprogramming of sensory receptors as a direct route from metabolic need to changed behavior.
The parallels to humans are suggestive. Many traditional diets rely on fermented foods that preserve nutrients and host beneficial microbes. The appeal of these foods may reflect ancient sensory strategies that helped animals locate microbial partners and nutrient-rich resources when dietary building blocks were scarce.
Overall, the research from the Ribeiro Lab connects metabolism, the microbiome, and sensory neuroscience: when essential amino acids are lacking, flies alter gene expression in olfactory systems to detect yeast and live bacteria that help restore nutritional balance.
Key Questions Answered:
A: They increase expression of smell receptors that detect odors from fermented foods and bacteria that supply or help produce essential amino acids.
A: Flies seek live, metabolically active bacteria that can enhance nutrient absorption and reproductive success when essential amino acids are scarce.
A: It reveals how internal nutritional needs can transcriptionally reprogram sensory systems, linking metabolism, behavior, and the microbiome in adaptive feeding strategies.
About this research
Author: Hedi Young
Source: Champalimaud Centre for the Unknown
Contact: Hedi Young – Champalimaud Centre for the Unknown
Image: Image credit: Neuroscience News
Original Research: Open access. “Lack of single amino acids transcriptionally tunes sensory systems to enhance microbiota intake” by Carlos Ribeiro et al., Current Biology
Abstract
Lack of single amino acids transcriptionally tunes sensory systems to enhance microbiota intake
Adequate intake of dietary essential amino acids (eAAs) is required for protein synthesis and normal metabolism. Deprivation of a single eAA is sufficient to increase protein intake in Drosophila melanogaster. How such nutritional needs are translated into behavioral drives is not fully understood. Transcriptome analysis of fly heads deprived of individual eAAs reveals both unique and shared transcriptional responses. Notably, Or92a is upregulated and contributes to yeast exploitation, while Ir76a is upregulated and is critical for feeding on commensal bacteria that improve the fitness of eAA-deprived flies. These findings uncover mechanisms by which transcriptional changes in sensory systems help animals adapt behaviorally and physiologically to amino acid challenges.