Increased ethylene production by overexpressing phosphoenolpyruvate carboxylase in the cyanobacterium PCC 6803.

BACKGROUND

Cyanobacteria can be metabolically engineered to convert CO to fuels and chemicals such as ethylene. A major challenge in such efforts is to optimize carbon fixation and partition towards target molecules.

RESULTS

The gene encoding an ethylene-forming enzyme was introduced into a strain of the cyanobacterium PCC 6803 with increased phosphoenolpyruvate carboxylase (PEPc) levels. The resulting engineered strain (CD-P) showed significantly increased ethylene production (10.5 ± 3.1 µg mL OD day) compared to the control strain (6.4 ± 1.4 µg mL OD day). Interestingly, extra copies of the native or the heterologous expression of PEPc from the cyanobacterium PCC 7002 () in the CD-P, increased ethylene production (19.2 ± 1.3 and 18.3 ± 3.3 µg mL OD day, respectively) when the cells were treated with the acetyl-CoA carboxylase inhibitor, cycloxydim. A heterologous expression of phosphoenolpyruvate synthase (PPSA) from in the CD-P also increased ethylene production (16.77 ± 4.48 µg mL OD day) showing differences in the regulation of the native and the PPSA from in .

CONCLUSIONS

This work demonstrates that genetic rewiring of cyanobacterial central carbon metabolism can enhance carbon supply to the TCA cycle and thereby further increase ethylene production.