We have performed the first comparative analysis of the potential of two physiologically-diverse model cyanobacteria, Synechococcus PCC 7002 (S.7002) and Synechococcus PCC 7942 (S.7942), for the photosynthetic production of four chemically-different high-value terpenes: two monoterpenes limonene and pinene, and two sesquiterpenes bisabolene and farnesene. We showed, for the first time, that S.7002 and S.7942 can produce farnesene and bisabolene, respectively. Both cyanobac-teria produced farnesene (S.7942 better than S.7002) more efficiently than the other tested terpenes (especially pinene the weakest produced terpene). S.7002 produced limonene better than bisabo-lene, whereas S.7942 produced bisabolene better than limonene. These findings suggest that S.7942 is better suited to produce sesquiterpenes than monoterpenes. Also interestingly, higher levels of terpenes were produced by S.7942 and S.7002 expressing a terpene-synthase gene from both a RSF1010-derived replicating plasmid and a neutral chromosomal site, as compared to ei-ther the plasmid alone or the chromosome alone. These results suggest that in both cyanobacteria the production of terpenes is more limited by the activity of terpene synthases than the abondance of terpene precursors. Finally, higher levels of terpenes were produced by S.7002 growing on urea (a frequent pollutant) as compared to nitrate (or ammonium) the standard nitrogen sources for cyanobacteria (more expensive than urea).

Terpenes are high-value chemicals which can be produced by engineered cyanobacteria from sustainable resources, solar energy, water and CO2. We previously reported that the euryhaline unicellular cyanobacteria Synechocystis PCC 6803 (S.6803) and Synechococcus PCC 7002 (S.7002) produce farnesene and limonene, respectively, more efficiently than other terpenes. In the present study, we attempted at enhancing 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 Cyanothece PCC 7425 increased farnesene production in S.6803, but not limonene production in S.7002. The overexpression of the crtE genes (synthesis or terpene precursors) from S.6803 or S.7002 did not increased farnesene production in S.6803. In contrast, the overexpression of the crtE 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 crtR and cruF genes (carotenoid synthesis) and phaAB genes (carbon storage) did not increase the production of farnesene in S.6803. Finally, as a containment strategy of genetically modified (GMO) strains of S.6803 we report that the deletion of the ccmK3K4 genes (carboxysome for CO2 fixation) did not affect the production of limonene but decreased the production of farnesene in S.6803.