Enhancement of photosynthetic capacity in Euglena gracilis by expression of cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase leads to increases in biomass and wax ester production

Takahisa Ogawa; Masahiro Tamoi; Ayako Kimura; Ayaka Mine; Harumi Sakuyama; Eriko Yoshida; Takanori Maruta; Kengo Suzuki; Takahiro Ishikawa; Shigeru Shigeoka

doi:10.1186/s13068-015-0264-5

Enhancement of photosynthetic capacity in Euglena gracilis by expression of cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase leads to increases in biomass and wax ester production

Biotechnol Biofuels. 2015 May 30:8:80. doi: 10.1186/s13068-015-0264-5. eCollection 2015.

Authors

Affiliations

¹ Department of Advanced Bioscience, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara, 631-8505 Japan ; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo, 102-0076 Japan.
² Department of Advanced Bioscience, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara, 631-8505 Japan.
³ Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo, 102-0076 Japan ; euglena Co., Ltd., 31F Iidabashi First Tower, 2-6-1 Koraku, Bunkyo-ku, Tokyo, 112-0004 Japan.
⁴ Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo, 102-0076 Japan ; Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane 690-8504 Japan.

Abstract

Background: Microalgae have recently been attracting attention as a potential platform for the production of biofuels. Euglena gracilis, a unicellular phytoflagellate, has been proposed as an attractive feedstock to produce biodiesel because it can produce large amounts of wax esters, consisting of medium-chain fatty acids and alcohols with 14:0 carbon chains. E. gracilis cells highly accumulate a storage polysaccharide, a β-1,3-glucan known as paramylon, under aerobic conditions. When grown aerobically and then transferred into anaerobic conditions, E. gracilis cells degrade paramylon to actively synthesize and accumulate wax esters. Thus, the enhanced accumulation of paramylon through the genetic engineering of photosynthesis should increase the capacity for wax ester production.

Results: We herein generated transgenic Euglena (EpFS) cells expressing the cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase (FBP/SBPase), which is involved in the Calvin cycle, to enhance its photosynthetic activity. FBP/SBPase was successfully expressed within Euglena chloroplasts. The cell volume of the EpFS4 cell line was significantly larger than that of wild-type cells under normal growth conditions. The photosynthetic activity of EpFS4 cells was significantly higher than that of wild type under high light and high CO2, resulting in enhanced biomass production, and the accumulation of paramylon was increased in transgenic cell lines than in wild-type cells. Furthermore, when EpFS cell lines grown under high light and high CO2 were placed on anaerobiosis, the productivity of wax esters was approximately 13- to 100-fold higher in EpFS cell lines than in wild-type cells.

Conclusion: Our results obtained here indicate that the efficiency of biomass production in E. gracilis can be improved by genetically modulating photosynthetic capacity, resulting in the enhanced production of wax esters. This is the first step toward the utilization of E. gracilis as a sustainable source for biofuel production under photoautotrophic cultivation.

Keywords: Biofuel; Biomass; Euglena gracilis; Fructose-1,6-/sedoheptulose-1,7-bisphosphatase; Paramylon; Photosynthesis; Wax ester.