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

Claudia Durall,Pia Lindberg,Peter Lindblad,Jianping Yu

doi:10.1186/s13068-020-1653-y

Claudia Durall, Pia Lindberg + Show 2 more

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https://doi.org/10.1186/s13068-020-1653-y

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Abstract

BackgroundCyanobacteria can be metabolically engineered to convert CO2 to fuels and chemicals such as ethylene. A major challenge in such efforts is to optimize carbon fixation and partition towards target molecules.ResultsThe efe gene encoding an ethylene-forming enzyme was introduced into a strain of the cyanobacterium Synechocystis 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−1 OD−1 day−1) compared to the control strain (6.4 ± 1.4 µg mL−1 OD−1 day−1). Interestingly, extra copies of the native pepc or the heterologous expression of PEPc from the cyanobacterium Synechococcus PCC 7002 (Synechococcus) in the CD-P, increased ethylene production (19.2 ± 1.3 and 18.3 ± 3.3 µg mL−1 OD−1 day−1, respectively) when the cells were treated with the acetyl-CoA carboxylase inhibitor, cycloxydim. A heterologous expression of phosphoenolpyruvate synthase (PPSA) from Synechococcus in the CD-P also increased ethylene production (16.77 ± 4.48 µg mL−1 OD−1 day−1) showing differences in the regulation of the native and the PPSA from Synechococcus in Synechocystis.ConclusionsThis work demonstrates that genetic rewiring of cyanobacterial central carbon metabolism can enhance carbon supply to the TCA cycle and thereby further increase ethylene production.

Highlights

Cyanobacteria can be metabolically engineered to convert CO2 to fuels and chemicals such as ethylene
Expression of efe and engineered strains The efe from Pseudomonas syringae expressed in our strains was stable and expressed when the promoter was induced with Ni2+
The CD-P strain was further engineered with another copy of the native pepc (4× pepc, CD-P1), one extra copy of the native ppsa (3× pepc, 2× ppsa, CD-P2) and an extra copy of the native pepc and ppsa (4× pepc, 2× ppsa, CD-P3)

Summary

Introduction

Cyanobacteria can be metabolically engineered to convert CO2 to fuels and chemicals such as ethylene. When RuBisCO performs the oxygenase reaction, where O 2 is produced as a secondary product of the photosynthesis reactions, the metabolite produced (glyoxylate) is toxic for the cells, leading to losing both carbon and energy. This process is called photorespiration [7]. The CCM consists in five different inorganic transporters (three for H CO3− and two Durall et al Biotechnol Biofuels (2020) 13:16 for CO2), the carboxysome and the carbonic anhydrase. Carbonic anhydrase converts bicarbonate into CO2 which can be used as substrate by RuBisCO. When the product 3-phosphoglycerate is formed, it can diffuse out of the carboxysome and be further metabolized in the cytoplasm [8] (Fig. 1)

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