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Alteration of Wax Ester Content and Composition in Euglena gracilis with Gene Silencing of 3-ketoacyl-CoA Thiolase Isozymes

Abstract

Euglena gracilis produces wax ester under hypoxic and anaerobic culture conditions with a net synthesis of ATP. In wax ester fermentation, fatty acids are synthesized by reversing beta-oxidation in mitochondria. A major species of wax ester produced by E. gracilis is myristyl myristate (14:0-14:0Alc). Because of its shorter carbon chain length with saturated compounds, biodiesel produced from E. gracilis wax ester may have good cold flow properties with high oxidative stability. We reasoned that a slight metabolic modification would enable E. gracilis to produce a biofuel of ideal composition. In order to produce wax ester with shorter acyl chain length, we focused on isozymes of the enzyme 3-ketoacyl-CoA thiolase (KAT), a condensing enzyme of the mitochondrial fatty acid synthesis pathway in E. gracilis. We performed a gene silencing study of KAT isozymes in E. gracilis. Six KAT isozymes were identified in the E. gracilis EST database, and silencing any three of them (EgKAT1-3) altered the wax ester amount and composition. In particular, silencing EgKAT1 induced a significant compositional shift to shorter carbon chain lengths in wax ester. A model fuel mixture inferred from the composition of wax ester in EgKAT1-silenced cells showed a significant decrease in melting point compared to that of the control cells.

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Abbreviations

CoA:

Coenzyme A

DSC:

Differential scanning calorimetry

EST:

Expressed sequence tag

FA:

Fatty acid

FAlc:

Fatty alcohol

FAME:

Fatty acid methyl ester

FAS II:

Type-2 fatty acid synthase

KAT:

3-Ketoacyl-CoA thiolase

RT:

Reverse transcription

TAG:

Triacylglycerol

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Acknowledgments

This work was supported by the Japan Science and Technology Agency (JST), PRESTO program. The authors thank Dr. Joseph Rodrigue for critical reading of the manuscript.

Conflict of interest

The authors declare that they have no competing interests.

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Correspondence to Masami Nakazawa.

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Nakazawa, M., Andoh, H., Koyama, K. et al. Alteration of Wax Ester Content and Composition in Euglena gracilis with Gene Silencing of 3-ketoacyl-CoA Thiolase Isozymes. Lipids 50, 483–492 (2015). https://doi.org/10.1007/s11745-015-4010-3

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  • DOI: https://doi.org/10.1007/s11745-015-4010-3

Keywords

  • Euglena gracilis
  • Wax ester fermentation
  • 3-Ketoacyl-CoA thiolase
  • Mitochondrial fatty acid synthesis
  • Acyl chain length modification
  • Algal lipids