A metabolic engineering strategy for producing conjugated linoleic acids using the oleaginous yeast Yarrowia lipolytica
Résumé
Conjugated linoleic acids (CLAs) have been found to have beneficial effects on human health when used as dietary supplements. However, their availability is limited because pure, chemistry-based production is expensive, and biology-based fermentation methods can only create small quantities. In an effort to enhance microbial production of CLAs, four genetically modified strains of the oleaginous yeast Yarrowia lipolytica were generated. These mutants presented various genetic modifications, including the elimination of beta-oxidation (pox1-6a dagger), the inability to store lipids as triglycerides (dga1a dagger dga2a dagger are1a dagger lro1a dagger), and the overexpression of the Y. lipolytica a dagger 12-desaturase gene (YlFAD2) under the control of the constitutive pTEF promoter. All strains received two copies of the pTEF-oPAI or pPOX-oPAI expression cassettes; PAI encodes linoleic acid isomerase in Propionibacterium acnes. The strains were cultured in neosynthesis or bioconversion medium in flasks or a bioreactor. The strain combining the three modifications mentioned above showed the best results: when it was grown in neosynthesis medium in a flask, CLAs represented 6.5% of total fatty acids and in bioconversion medium in a bioreactor, and CLA content reached 302 mg/L. In a previous study, a CLA degradation rate of 117 mg/L/h was observed in bioconversion medium. Here, by eliminating beta-oxidation, we achieved a much lower rate of 1.8 mg/L/h.