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Inhibition of starch synthesis results in overproduction of lipids in Chlamydomonas reinhardtii

Authors

  • Yantao Li,

    1. Department of Applied Sciences and Mathematics, Arizona State University, Polytechnic Campus, 7001 E. Williams Field Road, Mesa, Arizona 85212; telephone: 480-727-1484; fax: 480-727-1475
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  • Danxiang Han,

    1. Department of Applied Sciences and Mathematics, Arizona State University, Polytechnic Campus, 7001 E. Williams Field Road, Mesa, Arizona 85212; telephone: 480-727-1484; fax: 480-727-1475
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  • Guangrong Hu,

    1. Department of Applied Sciences and Mathematics, Arizona State University, Polytechnic Campus, 7001 E. Williams Field Road, Mesa, Arizona 85212; telephone: 480-727-1484; fax: 480-727-1475
    2. Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Laoshan District, Qingdao, Shandong, China
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  • Milton Sommerfeld,

    1. Department of Applied Sciences and Mathematics, Arizona State University, Polytechnic Campus, 7001 E. Williams Field Road, Mesa, Arizona 85212; telephone: 480-727-1484; fax: 480-727-1475
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  • Qiang Hu

    Corresponding author
    1. Department of Applied Sciences and Mathematics, Arizona State University, Polytechnic Campus, 7001 E. Williams Field Road, Mesa, Arizona 85212; telephone: 480-727-1484; fax: 480-727-1475
    • Department of Applied Sciences and Mathematics, Arizona State University, Polytechnic Campus, 7001 E. Williams Field Road, Mesa, Arizona 85212; telephone: 480-727-1484; fax: 480-727-1475.
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Abstract

Starch and neutral lipids are two major carbon storage compounds in many microalgae and plants. Lipids are more energy rich and have often been used as food and fuel feedstocks. Genetic engineering of the lipid biosynthesis pathway to overproduce lipid has achieved only limited success. We hypothesize that through blocking the competing pathway to produce starch, overproduction of neutral lipid may be achieved. This hypothesis was tested using the green microalga Chlamydomonas reinhardtii and its low starch and starchless mutants. We discovered that a dramatic increase in neutral lipid content and the neutral lipid/total lipid ratio occurred among the mutants under high light and nitrogen starvation. BAFJ5, one of the mutants defective in the small subunit of ADP-glucose pyrophosphorylase, accumulated neutral and total lipid of up to 32.6% and 46.4% of dry weight (DW) or 8- and 3.5-fold higher, respectively, than the wild-type. These results confirmed the feasibility of increasing lipid production through redirecting photosynthetically assimilated carbon away from starch synthesis to neutral lipid synthesis. However, some growth impairment was observed in the low starch and starchless mutants, possibly due to altered energy partitioning in PSII, with more excitation energy dissipated as heat and less to photochemical conversion. This study demonstrated that biomass and lipid production by the selected mutants can be improved by physiological manipulation. Biotechnol. Bioeng. 2010;107: 258–268. © 2010 Wiley Periodicals, Inc.

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