Enhancement of docosahexaenoic acid production by overexpression of ATP-citrate lyase and acetyl-CoA carboxylase in Schizochytrium sp

Xiao Han; Zhunan Zhao; Ying Wen; Zhi Chen

doi:10.1186/s13068-020-01767-z

Enhancement of docosahexaenoic acid production by overexpression of ATP-citrate lyase and acetyl-CoA carboxylase in Schizochytrium sp

Biotechnol Biofuels. 2020 Jul 21:13:131. doi: 10.1186/s13068-020-01767-z. eCollection 2020.

Authors

Xiao Han¹, Zhunan Zhao¹, Ying Wen¹, Zhi Chen¹

Affiliation

¹ State Key Laboratory of Agrobiotechnology and Key Laboratory of Soil Microbiology, Ministry of Agriculture, College of Biological Sciences, China Agricultural University, Beijing, 100193 China.

Abstract

Background: Docosahexaenoic acid (DHA) is an important omega-3 long-chain polyunsaturated fatty acid that has a variety of physiological functions for infant development and human health. Although metabolic engineering was previously demonstrated to be a highly efficient way to rapidly increase lipid production, metabolic engineering has seldom been previously used to increase DHA accumulation in Schizochytrium spp.

Results: Here, a sensitive β-galactosidase reporter system was established to screen for strong promoters in Schizochytrium sp. Four constitutive promoters (EF-1α _p , TEF-1 _p , ccg1 _p , and ubiquitin _p ) and one methanol-induced AOX1 promoter were characterized by the reporter system with the promoter activity ccg1 _p > TEF-1 _p > AOX1 _p (induced) > EF-1α _p > ubiquitin _p . With the strong constitutive promoter ccg1 _p , Schizochytrium ATP-citrate lyase (ACL) and acetyl-CoA carboxylase (ACC) were overexpressed in Schizochytrium sp. ATCC 20888. The cells were cultivated at 28 °C and 250 rpm for 120 h with glucose as the carbon source. Shake-flask fermentation results showed that the overexpression strains exhibited growth curves and biomass similar to those of the wild-type strain. The lipid contents of the wild-type strain and of the OACL, OACC, and OACL-ACC strains were 53.8, 68.8, 69.8, and 73.0%, respectively, and the lipid yields of the overexpression strains were increased by 21.9, 30.5, and 38.3%, respectively. DHA yields of the wild-type strain and of the corresponding overexpression strains were 4.3, 5.3, 6.1, and 6.4 g/L, i.e., DHA yields of the overexpression strains were increased by 23.3, 41.9, and 48.8%, respectively.

Conclusions: Acetyl-CoA and malonyl-CoA are precursors for fatty acid synthesis. ACL catalyzes the conversion of citrate in the cytoplasm into acetyl-CoA, and ACC catalyzes the synthesis of malonyl-CoA from acetyl-CoA. The results demonstrate that overexpression of ACL and ACC enhances lipid accumulation and DHA production in Schizochytrium sp.

Keywords: ATP-citrate lyase; Acetyl-CoA carboxylase; Constitutive promoter; Docosahexaenoic acid; Schizochytrium sp.; β-Galactosidase reporter system.