A compound that protects transparent fish eggs from the sun’s rays has been produced in the lab by genetically altering bacteria to create so-called microbial cell factories. Easier production of gadusol brings the chemical one step closer to use as a more eco-friendly, transparent sunscreen for humans.

Gadusol is found in the eggs of zebrafish, salmon and sturgeon, as well as coral, where it protects organisms from ultraviolet damage. But it’s only found in small quantities so extracting it from organisms for use as a sunscreen is impractical.

A team led by at Jiangnan University, China, inserted genes from zebrafish into the bacterium Escherichia coli to give it the enzymes needed to synthesise gadusol. Then, by using small RNA molecules to dial up gadusol production in the bacteria and tweaking their growing conditions, they increased the yield by nearly 93 times, from 45.2 milligrams per litre of liquid growth medium to 4.2 grams per litre.

In experiments, gadusol displayed antioxidant properties comparable to vitamin C, suggesting it may help neutralise free radicals that cause damage in cells. The researchers did not respond to a request for interview from żěè¶ĚĘÓƵ.

Gadusol is transparent, unlike melanin, and yet is perfectly tuned to block out harmful UV rays from the sun, which makes it ideal for organisms hiding from prey. “I think we haven’t necessarily given it the praise that it deserves,” says at the University of Utah, who was part of a team that discovered gadusol’s role as a sunscreen in fish embryos. “This is a great molecule.”

Gagnon says further testing is needed, but the compound is likely to be safe for humans and the environment because so many animals already use it. Thanks to its transparency, it might also avoid the milky residue that some current sunscreens leave on the skin.

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“Everyone wants to hint that this is going to be a great sunscreen for humans,” says Gagnon. But he warns that there are two hurdles to overcome before gadusol can be commercialised. One is finding a way to manufacture it economically, which this new paper has gone some way to solving, and the second is finding a mixture of chemicals that bind it into a solution that works as a long-lasting application.

“The active ingredient could be gadusol, but I guarantee 99 per cent of what’s in that bottle of sunscreen someday in the future is going be just stuff to hold the gadusol to your skin so it doesn’t wash off,” says Gagnon. “There’s still a lot of work required on the material science side.”