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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 β-oxidation (pox1-6∆), the inability to store lipids as triglycerides (dga1∆ dga2∆ are1∆ lro1∆), and the overexpression of the Y. lipolytica ∆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 β-oxidation, we achieved a much lower rate of 1.8 mg/L/h.

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A bioreactor using membrane technologies was used to demonstrate the feasibility of in-situ bio-methanation coupled to industrial wastewater treatment for biogas upgrading. High biogas productivity (1.7 Nm 3 Biogas/m 3 Bioreactor/day) with high CH4 content (97.9%) was reached. In-situ bio-methanation did not affect the COD removal efficiency of anerobic digestion (>94%). Process resilience has been tested for both substrate overload and H2 intermittence injection. Recovery of high CH4 content after 7 days without H2 injection occurred within few hours. Influence of microbial community has been studied showing that both hydrogenotrophic and homoacetogenic-acetoclastic pathways were involved.

Past research has sought to improve the production of cyclopropane fatty acids by the oleaginous yeast Yarrowia lipolytica by heterologously expressing the E. coli fatty acid synthase gene and improving cultivation processes. Cyclopropane fatty acids display properties that hold promise for biofuel applications. The E. coli fatty acid synthase gene was introduced into several genetic backgrounds of the yeast Y. lipolytica to optimize lipid synthesis; the mean cyclopropane fatty acid productivity was 43 mg L−1 h−1 on glucose, and the production rate reached its maximum (3.06 g L−1) after 72 h of cultivation in a bioreactor. The best strain (JMY6851) overexpressed simultaneously the E. coli cyclopropane fatty acid synthase gene under a hybrid promoter (hp8d) and Y. lipolytica LRO1 gene. In fed-batch process using crude glycerol as carbon source, JMY6851 strain displayed high lipid accumulation (78% of dry cell weight) and high biomass production (56 g L−1). After 165 h of cultivation, cyclopropane fatty acids represented 22% of the lipids produced; cyclopropane fatty acid productivity (103.3 mg L−1 h−1) was maximal at 72.5 h of cultivation.

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Cyclopropane fatty acids, which can be simply converted to methylated fatty acids, are good unusual fatty acid candidates for long‐term resistance to oxidization and low‐temperature fluidity useful for oleochemistry and biofuels. Cyclopropane fatty acids are present in low amounts in plants or bacteria. In order to develop a process for large‐scale biolipid production, we expressed 10 cyclopropane fatty acid synthases from various organisms in the oleaginous yeast Yarrowia lipolytica, a model yeast for lipid metabolism and naturally capable of producing large amounts of lipids. The Escherichia coli cyclopropane fatty acid synthase expression in Y. lipolytica allows the production of two classes of cyclopropane fatty acids, a C17:0 cyclopropanated form and a C19:0 cyclopropanated form, whereas others produce only the C17:0 form. Expression optimization and fed‐batch fermentation set‐up enable us to reach a specific productivity of 0.032 g·L−1·hr−1 with a genetically modified strain containing cyclopropane fatty acid up to 45% of the total lipid content corresponding to a titre of 2.3 ± 0.2 g/L and a yield of 56.2 ± 4.4 mg/g.

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