For centuries, we’ve relied on a tiny fungus called brewer’s yeast to help us produce a rather essential trio: bread, beer, and wine. Now, scientists have genetically engineered it to produce Tetrahydrocannabinol (THC) and cannabidiol (CBD) – the key ingredients of marijuana.

Publishing their findings in Nature, the team modified yeast so that it contained a number of genes normally found in the marijuana plant. They engineered two different sets of yeast – one that could produce a substance called THCA and another that made CBDA. When these are heated, you get THC and CBD.    

In recent years, scientific research has shown marijuana to have a number of potential medical uses, from easing anxiety and PTSD to reducing epileptic seizures. Although we still have a lot to learn about its effects on the body, research suggests it is safer to use than alcohol and tobacco, so it’s perhaps not all that surprising that cannabis, its extracts, and THC-containing medicines are now legal in various countries and US states.

THC, the psychoactive compound in cannabis, is currently approved by the US Food and Drug Administration (FDA) to treat nausea experienced by patients undergoing chemotherapy and to increase the appetite of those suffering from AIDS. Meanwhile, CBD, which affects the brain without causing a high, is approved for the treatment of epileptic seizures in children.    

An obstacle for scientists trying to unlock the marijuana plant’s full potential is that the chemicals within it occur in very small quantities and are therefore difficult to extract. But yeast are little powerhouses that can churn out the substances for scientists to study and consumers to use.

“For the consumer, the benefits are high-quality, low-cost CBD and THC: you get exactly what you want from yeast,” said Jay Keasling, a University of California, Berkeley professor of chemical and biomolecular engineering and of bioengineering, in a statement. “It is a safer, more environmentally friendly way to produce cannabinoids.”

Growing marijuana plants damages the environment as outdoor farms pollute water with pesticides and fertilizers, while indoor growing arrangements use a great deal of energy to maintain artificial lighting and ventilation. Using yeast could massively reduce marijuana’s impact on the environment.

Intriguingly, the GM yeast also produces its own cannabinoids that aren’t made by the plant. According to Keasling, there is “the possibility of new therapies based on novel cannabinoids: the rare ones that are nearly impossible to get from the plant, or the unnatural ones, which are impossible to get from the plant.

“When you read about cases of patients who have seizures and are helped by CBD, especially children, you realize there is some value in these molecules, and that producing cannabinoids in yeast could really be great.”