Metabolic engineering of Synechocystis sp. PCC 6803 for improved bisabolene production

• Published in: Metabolic engineering communications Vol. 12; p. e00159
• Main Authors: Rodrigues, João S., Lindberg, Pia
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2021; Elsevier
• Subjects: biochemical pathways; biofuels; Bisabolene; carbon sinks; Escherichia coli; feedstocks; green chemistry; heterologous gene expression; High cell density; isomerases; MEP pathway; Metabolic engineering; metabolism; Special issue on Engineering Cyanobacteria edited by Peter Lindblad and Jens Krömer; Synechocystis; terpenoids; Metabolic engineering; Synechocystis; MEP pathway; Bisabolene; High cell density
• ISSN: 2214-0301; 2214-0301
• DOI: 10.1016/j.mec.2020.e00159

[Display omitted] Terpenoids are a wide class of organic compounds with industrial relevance. The natural ability of cyanobacteria to produce terpenoids via the methylerythritol 4-phosphate (MEP) pathway makes these organisms appealing candidates for the generation of light-driven cell factories for green chemistry. Here we address the improvement of the production of (E)-α-bisabolene, a valuable biofuel feedstock, in Synechocystis sp. PCC 6803 via sequential heterologous expression of bottleneck enzymes of the native pathway. Expression of the bisabolene synthase is sufficient to complete the biosynthetic pathway of bisabolene. Expression of a farnesyl-pyrophosphate synthase from Escherichia coli did not influence production of bisabolene, while enhancement of the MEP pathway via additional overexpression of 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and IPP/DMAPP isomerase (IDI) significantly increased production per cell. However, in the absence of a carbon sink, the overexpression of DXS and IDI leads to significant growth impairment. The final engineered strain reached a volumetric titre of 9 ​mg ​L−1 culture of bisabolene after growing for 12 days. When the cultures were grown in a high cell density (HCD) system, we observed an increase in the volumetric titres by one order of magnitude for all producing-strains. The strain with improved MEP pathway presented an increase twice as much as the remaining engineered strains, yielding more than 180 ​mg ​L−1 culture after 10 days of cultivation. Furthermore, the overexpression of these two MEP enzymes prevented the previously reported decrease in the bisabolene specific titres when grown in HCD conditions, where primary metabolism is usually favoured. We conclude that fine-tuning of the cyanobacterial terpenoid pathway is crucial for the generation of microbial platforms for terpenoid production on industrial-scale. •Overexpressing two bottleneck enzymes from MEP pathway doubles bisabolene titres.•Enhancing MEP pathway in the absence of a proper carbon sink compromised growth.•Growth of bisabolene-producing strains in HDC system increased titres by 10-fold.•Improving MEP pathway prevents decrease in specific titres of cells grown in HDC.•The best producing strain reached 180 ​mg ​L−1 bisabolene after 10 days growth in HDC.