Impact of Carbon Fixation, Distribution and Storage on the Production of Farnesene and Limonene in PCC 6803 and PCC 7002.

Terpenes are high-value chemicals which can be produced by engineered cyanobacteria from sustainable resources, solar energy, water and CO. We previously reported that the euryhaline unicellular cyanobacteria sp. PCC 6803 (S.6803) and sp. PCC 7002 (S.7002) produce farnesene and limonene, respectively, more efficiently than other terpenes. In the present study, we attempted to enhance farnesene production in S.6803 and limonene production in S.7002. Practically, we tested the influence of key cyanobacterial enzymes acting in carbon fixation (RubisCO, PRK, CcmK3 and CcmK4), utilization (CrtE, CrtR and CruF) and storage (PhaA and PhaB) on terpene production in S.6803, and we compared some of the findings with the data obtained in S.7002. We report that the overproduction of RubisCO from S.7002 and PRK from sp. PCC 7425 increased farnesene production in S.6803, but not limonene production in S.7002. The overexpression of the genes (synthesis of terpene precursors) from S.6803 or S.7002 did not increase farnesene production in S.6803. In contrast, the overexpression of the gene from S.6803, but not S.7002, increased farnesene production in S.7002, emphasizing the physiological difference between these two model cyanobacteria. Furthermore, the deletion of the and genes (carotenoid synthesis) and genes (carbon storage) did not increase the production of farnesene in S.6803. Finally, as a containment strategy of genetically modified strains of S.6803, we report that the deletion of the genes (carboxysome for CO fixation) did not affect the production of limonene, but decreased the production of farnesene in S.6803.