Humans discovered the ability of yeast to produce psychoactive materials (or in less scientific terms: alcohol) thousands of years ago. One theory goes as far as saying the discovery of how to prepare beer from a mixture of grain, yeast and water is what encouraged humans to begin domesticating plants – and led to the first Agricultural Revolution in Neolithic times, over 12,000 years ago.
Now, scientists from the University of California, Berkeley have been able to make these same yeasts produce a different type of mind-altering materials: The active ingredients found in marijuana, the cannabinoids tetrahydrocannabinol and cannabidiol – better known as THC and CBD.
This method of genetic engineering, as published in the scientific journal Nature at the end of February, causes brewer’s yeast (Saccharomyces cerevisiae) – which is used in making both beer and bread – to turn a sugar called galactose into THC, the main compound that causes the typical marijuana high. The genetically engineered yeast also produces CBD, another psychoactive ingredient in marijuana, but one that has the potential ability to relieve pain and reduce anxiety. CBD has drawn a huge amount of interest and investment in recent years for its supposed medicinal benefits.
The Berkeley scientists hope their new fermentation process will enable the easy, quick, cheap and more precision manufacture of THC, CBD and other active ingredients in marijuana, which are found in very small amounts in cannabis plants. Previous research showed how it is possible to introduce parts of the cannabinoid production process into the yeast, but the new study is the first that succeeded in reproducing the entire process.
Brewer’s yeast is one of the most-studied organisms. Scientists have already used it to produce commercial drugs against malaria, and have shown in the lab that yeasts can also manufacture opiates.
The cannabinoid production method is still far from commercial use. Cannabis financial analyst David Kideckel told the Nature website that “it will be another 18-24 months before synthetic cannabinoids are cost-effective enough to sell to either pharmaceutical companies or the general public.”
In order to make brewer’s yeast produce THC, the biologists, led by Jay Keasling, a professor of chemical and biomolecular engineering at Berkeley, edited the genome of the unicellular organism and added genes from five types of bacteria and genes from the marijuana plant. The yeast underwent 16 genetic changes to enable it to turn galactose into inactive forms of THC or CBD. Heating the cannabinoids then switches them into their active forms. The team produced roughly 8 milligrams per liter of THC and lower levels of CBD, reported Nature.
But these yields would have to increase by 100 times for the process to be commercially viable. Demetrix, a company founded by Keasling in 2015, is working on making the process more efficient and so far has increased the yield by several orders of magnitude, CEO Jeff Ubersax told Nature. The method could be used with not only yeasts, but with bacteria and algae, too. Others are trying to modify the marijuana plants themselves to increase purity and yields.
The scientists were also able to engineer the yeast to produce new cannabinoids that don’t exist in nature. The goal is to screen these compounds for potential medicinal properties – because they can then be patented, unlike already identified natural products – and drug companies are expected to take up this part of the challenge, because for legal reasons they have avoided researching cannabis products.
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