No eyes? No problem. Worms still avoid the blues

Worms don’t like the blues. At least not the blue-tinged toxic bacteria that are common in the environments where they live. But how does a bacteria-foraging worm — without eyes, photoreceptors, or the opsin genes that help animals perceive color — know to avoid the toxic, blue-reflecting bacterium known as Pseudomonas aeruginosa?

Until recently, Yale’s Michael Nitabach thought worms must recognize distinct chemosensory odors emitted by this bacterium. D. Dipon Ghosh, a former graduate student in Nitabach’s lab, had a different hypothesis. He wondered if worms could also have the capacity to somehow sense colors.

Image credit: ThisIsEngineering (Source:

I told him he was being ridiculous,” said Nitabach, professor of cellular and molecular physiology, of genetics and of neuroscience.

But, it turns out, Ghosh was right. In the March 5 issue of the journal Science, Nitabach and Ghosh describe how worms manage to detect color despite compltely lacking a basic visual system.

Their discovery expands our current ideas about the possible range of sensitivities to light that cells and organisms — even those that lack the proteins required for vision — might have .

In a series of experiments, the research team exposed different strains of the worm Caenorhabditis elegans to either the colorful P. aeruginosa bacteria in white light or to colorless E. coli bacteria in light of varying color spectra. They found that some family members require both a chemical indicator and a specific color in order to avoid the toxic bacterIa, while other family members avoid the bacteria based on the color alone. In all cases, the worm’s decision about whether to avoid the bacteria was influenced by the color of light in its environment.

The lab also identified two genes in the worms that are associated with the ability to peceive color. In mammals, these same genes help regulate the response to stress and can be activated by exposure to ultraviolet light.

What the worm is doing is something very smart,” Nitabach said. “[It is] trying to generate a more accurate picture of external reality by employing multiple senses at same time.”

By Bill Hathaway

*Source: Yale University

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