Enhancement of the productivity of free dihomo-γ-linolenic acid via co-overexpression of elongase and two desaturase genes in Aspergillus oryzae

• Published in: Journal of bioscience and bioengineering Vol. 130; no. 5; pp. 480 - 488
• Main Authors: Tamano, Koichi, Yasunaka, Yuta, Kamishima, Misaki, Itoh, Ayano, Miura, Ai, Kan, Eiichiro, Koyama, Yasuji, Tamura, Tomohiro
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2020
• Subjects: Aspergillus oryzae; Co-overexpression; Desaturase; Elongase; Free dihomo-γ-linolenic acid; Productivity enhancement; Elongase; Free dihomo-γ-linolenic acid; Productivity enhancement; Co-overexpression; Aspergillus oryzae; Desaturase
• ISSN: 1389-1723; 1347-4421
• DOI: 10.1016/j.jbiosc.2020.07.004

Free dihomo-γ-linolenic acid (DGLA), a polyunsaturated free fatty acid (FFA), is a precursor of the eicosanoid prostaglandin E1 and is expected to be a source material for artificial production. We previously constructed the Aspergillus oryzae mutant strain ARA1 that produced free DGLA from the disruptant of faaA, an acyl-CoA synthetase gene, where FFA productivity increased by 9.2-fold compared with that of the wild-type strain. Here, we aimed to achieve enhancement of free DGLA productivity. Because saturated FFAs, such as palmitic acid and stearic acid, accounted for about 45% and 25% of total FFAs produced by ARA1, respectively, we used a strategy to facilitate elongation and desaturation of these FFAs to oleic acid and linoleic acid by overexpressing genes encoding elongase, Δ9-desaturase, and Δ12-desaturase originally expressed in A. oryzae. Ten genes were predicted to encode desaturases, and their overexpression DNA constructs were introduced into ARA1. AO090001000224 and AO090011000488 facilitated Δ12-desaturation and Δ9-desaturation most, respectively, following overexpression. Next, ARA1 strain was modified to DGLA1cre strain for producing free DGLA as a final product, and co-overexpression of these two desaturase genes was then introduced to DGLA1cre. Moreover, single overexpression of two genes predicted to encode elongases was additionally introduced, and only AO090003000572 facilitated elongation. Consequently, in the co-overexpression mutant of AO090001000224, AO090011000488, and AO090003000572, free DGLA content ratio increased by 1.8-fold from ARA1 to 14.5%, and the productivity also increased by 1.8-fold to 0.086 mmol/g-dry-cell-weight. The yield was 284 mg/L. These findings provided insights into strategies for improving microbial production of polyunsaturated FFAs.