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

Nakazawa, Masami, Andoh, Hiroko, Koyama, Keiichiro, Watanabe, Yomi, Nakai, Takeo, Ueda, Mitsuhiro, Sakamoto, Tatsuji, Inui, Hiroshi, Nakano, Yoshihisa, Miyatake, Kazutaka
Lipids 2015 v.50 no.5 pp. 483-492
Euglena gracilis, adenosine triphosphate, beta oxidation, biodiesel, carbon, databases, expressed sequence tags, fatty acids, fermentation, fluid mechanics, gene silencing, isozymes, melting point, mitochondria, oxidative stability
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.