Engineered Terpenoid Production in Synechocystis sp. PCC 6803 Under Different Growth Conditions

ABSTRACTTerpenoids are the largest class of natural products and have applications in a wide variety of industries. Many terpenoids can be chemically synthesized or extracted from plants, but this is often uneconomical or unsustainable. An alternative production method relies on the heterologous expression of terpene synthase enzymes in cyanobacteria, producing the desired compounds directly from carbon dioxide. In this work, a patchoulol synthase enzyme from Pogostemon cablin (patchouli) was expressed in the cyanobacterium Synechocystis sp. PCC 6803 under four different growth conditions. Final yields of patchoulol from each growth condition were as follows: 249 μg L−1, photoautotrophic growth; 6.5 μg L−1, mixotrophic growth; 27.6 μg L−1, bicarbonate low light; 31.7 μg L−1, bicarbonate high light. By comparing patchoulol production across growth conditions, we identified a significant positive correlation between the production of photopigments (chlorophyll and carotenoids) and the production of patchoulol. Importantly, this relationship was found to be stronger than the correlation between cell density and patchoulol production across growth conditions, which was not statistically significant. The relationship between photopigments and patchoulol should be generalizable to the production of other terpenoids that rely on expression of the endogenous methylerythritol phosphate (MEP) pathway in cyanobacteria. Based on the results of this work, we propose a strategy for maximizing terpenoid production in cyanobacteria by optimizing growth conditions for photopigment production, resulting in increased flux through the MEP pathway. This strategy has the advantage of facile photopigment quantification using simple spectroscopic methods, and optimized growth conditions can be utilized in partnership with conventional terpenoid production strategies to further improve yields.