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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.

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.

The effects of stimulation of Saccharomyces cerevisiae cells in an aqueous suspension by pulsed electric field (PEF) with electric field strength E = 20–2,000 V cm⁻¹ and effective PEF treatment time t PEF = 10⁻⁵–1 s were investigated. At relatively high electric field strengths (E > 1,000 V cm⁻¹) and moderate times of PEF treatment (t PEF > 100 μs), the extraction of ionic components from yeast was observed, which can be related to electroporation of cell membranes. Petri dishes counting revealed dependency of the colony sizes on the time of preliminary fermentation t f and power consumption W. The “logarithmic” and “saturated” types of electrostimulation were distinguished. At “logarithmic” electrostimulation (10⁻⁷ J mL⁻¹ < W < 10⁻¹ J mL⁻¹), the viability of yeast cells increased with the increase of power consumption and was higher for longer fermentation (t f = 24 h). However, at “saturated” electrostimulation (10⁻¹ J mL⁻¹ < W < 10¹ J mL⁻¹), the viability of yeast cells was noticeably higher for t f = 1 h than for t f = 24 h. The impact of preliminary fermentation time and PEF protocol on biological activity of cells and consumption of nutrients was also discussed.

This paper presents a rapid less than 2 min and low-cost method involving the use of alkali solution to capture the acidic gasses from a biogas, thereby providing an estimate of the percentage of non-acidic gasses. Such a method was mentioned in the literature but never fully described or optimized. After sampling an aliquot of gas from bioprocess, gas was injected in a sealed flask with a 3 M NaOH solution, and after equilibrium was obtained, the non-acidic gas volume was measured. The method was first calibrated with certified gasses with an accuracy observed between 98 and 105 %. Regarding the validation step, certified standard gas mixtures and nine biogas-laboratory batch reactors were used, the overall accuracy reported was 103 + 3 %. This rapid and low-cost method may either be used in laboratory conditions as a quick and low cost alternative to standard analysis equipment or in addition as a routine field control method used on full-scale plants.