Yeast is a loved fungus; it’s the reason we have bread and beer which have been staples in many communities for thousands of years. Science has revealed that there’s more to yeast than fermenting wheat and barley. Researchers are exploring yeast as a potential biofactory for producing cannabinoids such as tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA), delta-9-tetrahydrocannabinol (THC), and cannabidiol (CBD), among others.
Cannabigerolic acid (CBGA), considered to be the mother of all cannabinoids, is produced by the alkylation of olivetolic acid (OA) and geranyl pyrophosphate (GPP). [1] Olivetolic acid is created through the condensation of hexanoic acid with three molecules of malonic acid in the malonate pathway. THCA synthase catalyzes the reaction that converts CBGA into THCA, and hydrogen peroxide, produced alongside, has toxic effects on yeast cells.
The synthesis of THCA in yeast was achieved using heterologous genes from Cannabis sativa and Streptomyces spp that were cloned into the yeast Saccharomyces cerevisiae. [2] The researchers examined anabolic pathways leading to the production of phytocannabinoid precursors: olivetolic acid and CBGA. They also identified potential metabolic bottlenecks.
The researchers used a mathematical formula to create an in silico model for synthesizing THCA in S. cerevisiae, which has. The yeast used has industrial GRAS status and has been used in the production of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP).
This yeast has several beneficial physiological properties, well known genetics, and can easily be manipulated genetically. It does well in acidic conditions and its suitability for THCA production is of interest because S. cerevisiae produces high yields of terpenoids, IPP, and DMAPP; has a high biocatalytic activity rate (low concentration of misfolded proteins); and a reduced risk of self-toxification.
The researchers found that the production of hexanoic acid is a limiting step toward the production of THCA and other cannabinoids. It appears that yeast is slow, and therefore inefficient, in producing GPP and hexanoic acid. This is the major bottleneck since only 5% of hexanoic acid is converted into olivetolic acid, a precursor of CBGA.
This amount doesn’t satisfy the demand for olivetolic acid that’s needed for prenylation with GPP. Glycosylation or feeding with synthetic olivetolic acid are potential routes for dealing with this bottleneck that need further exploration.
All limitations considered, even though yeast can be used in THCA production, it cannot compete with natural cannabis which produces THCA concentrations exceeding 20%. That said, yeast remains an ideal platform for the smart bioengineering of minor cannabinoids that exist in cannabis in concentrations that may not exceed 0.5%. The researchers remarked that “the driving force in bioengineering 2.0 is to make kg and not mg to be competitive with plants.”
Image Source
https://commons.wikimedia.org/wiki/File:Yeast_culture_plate.JPG
References
[1] Blatt-Janmaat K, Qu Y. The biochemistry of phytocannabinoids and metabolic engineering of their production in heterologous systems. Int J Mol Sci. 2021;22(5):2454. [journal impact factor = 5.923; times cited = 10][2] Thomas F, Schmidt C, Kayser O. Bioengineering studies and pathway modeling of the heterologous biosynthesis of tetrahydrocannabinolic acid in yeast. Appl Microbiol Biotechnol. 2020;104(22):9551-9563. [journal impact factor = 5.560; times cited = 7]
