Metabolic Engineering for Efficient Ketocarotenoid Accumulation in the Green Microalga Chlamydomonas reinhardtii

Sofia Amendola, Jacob S. Kneip, Florian Meyer, Federico Perozeni, Stefano Cazzaniga, Kyle J. Lauersen, Matteo Ballottari, Thomas Baier

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Astaxanthin is a valuable ketocarotenoid with various pharmaceutical and nutraceutical applications. Green microalgae harbor natural capacities for pigment accumulation due to their 2-C-methyl-d-erythritol 4-phosphate (MEP) pathway. Recently, a redesigned ß-carotene ketolase (BKT) was found to enable ketocarotenoid accumulation in the model microalga Chlamydomonas reinhardtii, and transformants exhibited reduced photoinhibition under high-light. Here, a systematic screening by synthetic transgene design of carotenoid pathway enzymes and overexpression from the nuclear genome identified phytoene synthase (PSY/crtB) as a bottleneck for carotenoid accumulation in C. reinhardtii. Increased ß-carotene hydroxylase (CHYB) activity was found to be essential for engineered astaxanthin accumulation. A combined BKT, crtB, and CHYB expression strategy resulted in a volumetric astaxanthin production of 9.5 ± 0.3 mg L–1 (4.5 ± 0.1 mg g–1 CDW) in mixotrophic and 23.5 mg L–1 (1.09 mg L–1 h–1) in high cell density conditions, a 4-fold increase compared to previous reports in C. reinhardtii. This work presents a systematic investigation of bottlenecks in astaxanthin accumulation in C. reinhardtii and the phototrophic green cell factory design for competitive use in industrial biotechnology.
Original languageEnglish (US)
JournalACS Synthetic Biology
StatePublished - Feb 23 2023

Bibliographical note

KAUST Repository Item: Exported on 2023-02-27
Acknowledgements: This research was supported by the ERC Starting Grant SOLENALGAE (679814) and the University of Verona grant no. JPVR2018BALLOTTARI to M.B. Funding to K.J.L. was provided by the King Abdullah University of Science and Technology (KAUST) baseline research funding. F.M. acknowledges funding by BMBF project KaroTec (grant number: 03VP09460). The authors would like to express their thanks to Prof. Dr. Ralph Bock for providing strain UVM4 and to Tim Prausner for performing TLC.

ASJC Scopus subject areas

  • Biomedical Engineering
  • Biochemistry, Genetics and Molecular Biology (miscellaneous)


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