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Genes from the cannabis plant have been added to yeast strains to enable them to make cannabinoids, key chemicals from the plant that have therapeutic value.

The “cannayeasts” should make it possible to turn sugar into pure forms of many different cannabinoids, and to do so more cheaply and with less environmental damage than farming.

“It gives us access to all these rare cannabinoids that might even be better therapeutics,” says Jay Keasling at the University of California, Berkeley, who led the team behind the work.

Our bodies produce cannabinoids to help regulate everything from memory to appetite. Marijuana plants make more than 100 chemicals that can also bind to the cannabinoid receptors in our nervous system.

The main cannabinoid in cannabis is tetrahydrocannabinol (THC), which is what makes people feel “stoned” when they take cannabis. The next most abundant is cannabidiol (CBD). This helps reduce the symptoms of some forms of epilepsy, and may be useful for treating a few other conditions too. Various forms of CBD, such as e-spliffs, have become fashionable lately, and are claimed to have all kinds of benefits. (CBD is legal in many countries where cannabis remains illegal.)

But extracting pure CBD or THC from plants, or making it from scratch, is difficult and expensive. Keasling says the genetically modified yeasts will produce pure cannabinoids more cheaply.

“We can beat the economics of growing it on farms,” he says. “In part, it’s because there is a lot of manual labour in clipping the buds and all the things you have to do to grow cannabis.”

What’s more, producing chemicals in yeast is less environmentally damaging than growing large amounts of a plant just to extract a chemical that is present in tiny quantities, he says.

Accidental discovery

He and his team discovered by accident that they can produce previously unknown cannabinoids by changing what the yeasts are fed. So by making it possible to produce and study rare and formerly unknown cannabinoids, the cannayeasts might lead to new treatments for a range of disorders.

“There may be a market for this,” says Peter Reynolds of the CLEAR Cannabis Law Reform group, which campaigns to legalise cannabis in the UK. “Frankly, I don’t understand why. It’s not a difficult plant to grow. It’s called weed for a reason.”

Reynolds is also sceptical about the need for pure cannabinoids. He says the beneficial effects of cannabis depend on a combination of these chemicals, an idea known as the entourage effect.

“To my knowledge, there’s no scientific evidence that this is the case,” responds Keasling. And even if the entourage effect does exist, pharma companies want pure molecules so they can do pure science, he says.

Keasling and his team have formed a company called to commercialise the cannayeasts. At least two other companies, in California and Hyasynth in Canada, have said they are also working on making cannabinoids in yeast, but they have yet to publish any results.

Another company, , is developing yeasts that can produce opioids. But if these strains were ever stolen and got into the hands of illegal producers, they could transform the black market.

A growing range of food ingredients such as vanilla and saffron can also be brewed in this way. And Keasling’s team is best known for creating a yeast that produces the antimalarial drug artemisinin.