Color-dependent foraging in C. elegans integrates chromoprotein photosensitization with bacterial metabolic cues

Animals utilize color cues to navigate complex environments, but how color perception guides food selection in organisms without eyes is not well understood. This study demonstrates that Caenorhabditis elegans, an eyeless organism, prefers to consume red bacteria while avoiding blue chromoprotein-producing bacteria across different bacterial backgrounds and wild isolates.

This color-dependent foraging remains consistent even in darkness and is not reliant on photoreceptor cells, suggesting an alternative mechanism beyond traditional photoreception.

The researchers found that purified chromoproteins and bacterial metabolite fractions alone can elicit the same preference, indicating that there are both chromatic and post-ingestive metabolic cues involved. Blue chromoproteins are responsible for generating singlet oxygen, which causes oxidative stress and alters bacterial tryptophan and pterin metabolism.

In contrast, red food leads to an increase in serotonin production and feeding-associated neuropeptide signaling. Disrupting serotonin biosynthesis or neuropeptide processing removes the color preference in the C. elegans.

In conclusion, this study reveals a novel sensory strategy in C. elegans, where wavelength-selective pigment photochemistry converts microbial color into metabolic information. This information is then integrated through gut-brain neuroendocrine signaling to guide foraging behavior in an organism without eyes.