Cyanobacteria metabolic engineering for photosynthetic terpene production ; Ingénierie métabolique de cyanobactéries pour la production photosynthétique de terpènes

Cyanobacteria can produce compounds of industrial interest, from solar energy, water (even polluted) and CO₂. In the laboratory we are interested in terpenes because they are volatile (easy to harvest), have good smells ("cosmetic interest") and a high energy density ("biofuel interest").Our approach takes advantage of the physiological diversity of cyanobacteria and the chemical diversity of terpenes with the future objective of generating economically viable production. Thus, I worked with two different model cyanobacteria, Synechocystis PCC 6803 (S.6803) and Synechococcus PCC 7002 (S.7002), which are capable of growing in salt water (more abundant than fresh water). We have constructed genetically stable terpene producing strains. We have shown, for the first time, that S.6803 can produce farnesene, and also santalene (never produced by a cyanobacterium before (Blanc-Garin et al., 2022), and that S.7002 can produce farnesene (Chenebault et al., 2023). In these two cyanobacteria, the production of terpenes increases in parallel with the expression of genes (ts) coding for terpene synthases (Blanc-Garin et al., 2022; Chenebault et al., 2023). The production of terpenes in S.6803 cultivated in nitrate (the classic nitrogen source) or in urea (less expensive) is equivalent. On the other hand, in S.7002, the production of terpenes is better with urea (Blanc-Garin et al., 2022; Chenebault et al., 2023).As S.6803 produces farnesene better than other terpenes (and better than S.7002), and S.7002 produces limonene better than S.6803 (Chenebault et al., 2023), we worked to improve these producers. I analyzed the influence of carbon fixation, distribution and/or storage on terpene production. Overexpression of the genes encoding RuBisCO and phosphoribulokinase increased the production of farnesene in S.6803, but not limonene in S.7002 (manuscript in preparation). On the other hand, farnesene production in S.6803 does not increase when trying to save carbon, by interrupting the synthesis of polyhydroxybutyrates or by ...