Light/dark cycling causes delayed lipid accumulation and increased photoperiod-based biomass yield by altering metabolic flux in oleaginous Chlamydomonas sp

Yuichi Kato; Yusuke Fujihara; Christopher J Vavricka; Jo-Shu Chang; Tomohisa Hasunuma; Akihiko Kondo

doi:10.1186/s13068-019-1380-4

Light/dark cycling causes delayed lipid accumulation and increased photoperiod-based biomass yield by altering metabolic flux in oleaginous Chlamydomonas sp

Biotechnol Biofuels. 2019 Feb 21:12:39. doi: 10.1186/s13068-019-1380-4. eCollection 2019.

Authors

Yuichi Kato¹, Yusuke Fujihara², Christopher J Vavricka², Jo-Shu Chang^{3

4}, Tomohisa Hasunuma^{1

2}, Akihiko Kondo^{1

2

5}

Affiliations

¹ 1Engineering Biology Research Center, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.
² 2Graduate School of Science, Technology and Innovation, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.
³ 3Department of Chemical Engineering, National Cheng Kung University, Tainan, 701 Taiwan.
⁴ 4Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, 701 Taiwan.
⁵ 5Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe, 657-8501 Japan.

Abstract

Background: Light/dark cycling is an inevitable outdoor culture condition for microalgal biofuel production; however, the influence of this cycling on cellular lipid production has not been clearly established. The general aim of this study was to determine the influence of light/dark cycling on microalgal biomass production and lipid accumulation. To achieve this goal, specific causative mechanisms were investigated using a metabolomics approach. Laboratory scale photoautotrophic cultivations of the oleaginous green microalga Chlamydomonas sp. JSC4 were performed under continuous light (LL) and light/dark (LD) conditions.

Results: Lipid accumulation and carbohydrate degradation were delayed under the LD condition compared with that under the LL condition. Metabolomic analysis revealed accumulation of phosphoenolpyruvate and decrease of glycerol 3-phosphate under the LD condition, suggesting that the imbalance of these metabolites is a source of delayed lipid accumulation. When accounting for light dosage, biomass yield under the LD condition was significantly higher than that under the LL condition. Dynamic metabolic profiling showed higher levels of lipid/carbohydrate anabolism (including production of 3-phosphoglycerate, fructose 6-phosphate, glucose 6-phosphate, phosphoenolpyruvate and acetyl-CoA) from CO₂ under the LD condition, indicating higher CO₂ fixation than that of the LL condition.

Conclusions: Photoperiods define lipid accumulation and biomass production, and light/dark cycling was determined as a critical obstacle for lipid production in JSC4. Conversions of phosphoenolpyruvate to pyruvate and 3-phosphoglycerate to glycerol 3-phosphate are the candidate rate-limiting steps responsible for delayed lipid accumulation. The accumulation of substrates including ribulose 5-phosphate could be explained by the close relationship of increased biomass yield with enhanced CO₂ fixation. The present study investigated the influence of light/dark cycling on lipid production by direct comparison with continuous illumination for the first time, and revealed underlying metabolic mechanisms and candidate metabolic rate-limiting steps during light/dark cycling. These findings suggest promising targets to metabolically engineer improved lipid production.

Keywords: Biofuel; Biomass; Carbohydrate; Chlamydomonas; Light/dark cycling; Lipid; Metabolic profiling; Microalgae; Photoperiod.