These roundworms have no eyes, yet can ‘sense’ blue colour and scamper from it

Scientists say findings about C. elegans, a type of roundworm, shows they forage using colour cues and avoid the colour blue.

C. elegans | Wikimedia Commons

Bengaluru: Scientists studying how the roundworm Caenorhabditis elegans can distinguish between toxic bacteria and ones that are safe to consume have discovered that these blind worms can actually detect blue pigment.

The transparent roundworm, a kind of nematode (a classification of worms), lacks not only eyes but also the genes required for proteins that perform colour detection.

However, the researchers found that in well-lit settings, the C. elegans was able to move away quickly from blue coloured pigment.

They tested the hypothesis by changing the pigment colour to beige and also performing the same experiment in the dark, and discovered that the worms moved away much slower in both conditions.

The study was led by Dr D. Dipon Ghosh and was published in the journal Science last week.

What the study found

Previous research has shown that the C. elegans has light detecting cells that is highly efficient in capturing light, although it does not have eyes.

The latest experiment confirmed this. When researchers turned off the lights, the worms moved much slower. But in the presence of light, they reacted faster, especially to move away from toxin-producing bacteria P. aeruginosa.

Studies have even shown that too much visible light and ultraviolet light reduces their lifespan. However, their detection of colour had not been studied or observed before.

When the researchers put the worms near a mutated strain of the P. aeruginosa bacteria that was beige in colour, even under light the worms moved rather slowly and did not move away faster. But when a blue pigment called pyocyanin was added to E. coli bacteria, one of the worm’s common sources of food, they scrambled to get away from the microbes under well-lit conditions.

Further follow up experiments showed that although the worms displayed discomfort or inhibition to bacteria with toxins but without colour, they moved the fastest to get away when the colour blue was visible.

The researchers tried to replicate the findings with other nematodes, and found that some were sensitive to the colour while some were not.

Genetic analysis revealed that two genes, jkk-1 and lec-3, affected the worms’ behaviour. They confirmed this by genetically mutating worms lacking these genes to include them, and observed the mutated worms avoiding blue pigment.

It is unclear how the worms with no vision can detect the blue pigment, but the authors state that the findings indicate that the worms could actually be foraging using colour cues.

About C. elegans

C. elegans is a model organism, or one that is studied extensively in the lab to understand biological phenomena. Other examples include E. coli bacterium and the Drosophila melanogaster or the fruit fly. C. elegans was the first multicellular organism to have its entire genome sequenced and to have a complete map of its connectome — the neural connections coming from the brain.

The worm lacks both a respiratory and a circulatory system, and does not have blood. It does however have a mouth and an intestine.

It is commonly found in nutrient-rich and bacteria-rich environments, such as the soil and other decaying organic matter. For laboratory studies, these worms are cultivated in compost.

Further research is expected to reveal this likely evolutionary response to a pigment of a colour that is not commonly found in nature.

(Edited by Manasa Mohan)