Biotechnology and Bioprocess Engineering 2023; 28(2): 274-280  
Metabolic Engineering for Redirecting Carbon to Enhance the Fatty Acid Content of Synechocystis sp. PCC6803
Danbee Yoo, Seong-Joo Hong, Seonghoon Yun, Mi-Jin Kang, Byung-Kwan Cho, Hookeun Lee, Hyung-Kyoon Choi, Dong-Myung Kim, and Choul-Gyun Lee
Danbee Yoo, Seong-Joo Hong, Seonghoon Yun, Mi-Jin Kang, Choul-Gyun Lee*
Department of Biological Engineering, Inha University, Incheon 22212, Korea
Tel: +82-32-860-8997; Fax: +82-32-872-4046
E-mail: leecg@inha.ac.kr
Seong-Joo Hong, Seonghoon Yun, Choul-Gyun Lee
Industry-Academia Interactive R&E Center for Bioprocess Innovation, Inha University, Incheon 22212, Korea
Byung-Kwan Cho
Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Daejeon 34051, Korea
Hookeun Lee
College of Pharmacy, Gachon University, Incheon 21936, Korea
Hyung-Kyoon Choi
College of Pharmacy, Chung-Ang University, Seoul 06974, Korea
Dong-Myung Kim
Department of Fine Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 34134, Korea
Received: December 14, 2020; Revised: March 31, 2023; Accepted: April 4, 2023; Published online: April 30, 2023.
© The Korean Society for Biotechnology and Bioengineering. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Biofuels produced by photosynthetic microorganisms are considered a renewable, sustainable, and eco-friendly alternative to fossil fuels that cause a negative environmental impact. Microalgae can accumulate the end-products and precursors required for biodiesel production with higher productivity and better sustainability than conventional energy crops. High lipid content, a metabolic rate faster than that of higher plants, and an ability to grow under poor conditions are the desirable characteristics of microalgae that make them an efficient feedstock for the economical production of biodiesel. In this study, we attempted to improve the lipid content of microalgae by metabolically redirecting the carbon flux from carbohydrate or cyanophycin synthesis to lipid synthesis. Synechocystis sp. PCC6803, a model microalga for genetic modification studies, was used to study the effect of deletion of specific metabolic genes and the introduction of an exogenous gene. In Synechocystis, glycogen and cyanophycin primarily store carbon, and are accumulated in the absence of nitrogen sources. The genes encoding the enzymes ADP-glucose pyrophosphorylase (glgC: slr1176) and cyanophycin synthase (cphA: slr2002), which are involved in glycogen and cyanophycin synthesis, respectively, were knocked out to block cyanophycin or glycogen synthesis and increase the carbon pool for lipid synthesis. Blocking glycogen synthesis decreased the carbohydrate content by up to 71% and increased the fatty acid content by up to 24% compared with the wild-type strain cultivated under nitrate-deficient conditions. Blocking cyanophycin synthesis did not affect the fatty acid content. Our results could be used to construct genetically engineered Synechocystis for the large-scale production of fatty acids.
Keywords: cyanobacteria, fatty acids, biodiesel, Synechocystis

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