Disrupting a phospholipase A2 gene increasing lipid accumulation in the oleaginous yeast Yarrowia lipolytica.

AIMS: Phospholipase A2 (PLA2 ) is a diverse superfamily that hydrolyzes fatty acyl ester bonds at the sn-2 position of phospholipids. The correlation between phospholipid metabolism and the anabolism of neutral lipids remains unclear in yeasts. This study aims to explore the effects of PLA2 on lipid accumulation in the oleaginous yeast Yarrowia lipolytica. METHODS AND RESULTS: This study identified an actively expressed phospholipase A2 gene (PLA2-3, YAIL0_E16060g) in Y. lipolytica by quantitative PCR analysis. The gene PLA2-3 was disrupted in the strain po1gΔKu70 by homologous recombination and in the strain po1g-G3 by a CRISPR-Cas9 system, which caused an increase in stress sensitivity while the cell growth was not altered under fermentative conditions. Lipid production was performed in both flasks and bioreactors. The results showed that the lipid titre and lipid content were improved over 25% and 8-30%, respectively, in PLA2-3 disrupted strains compared to the controls. CONCLUSIONS: Disruption of the phospholipase PLA2-3 gene could effectively improve lipid production in Y. lipolytica. SIGNIFICANCE AND IMPACT OF THE STUDY: This study presented a strategy on improving the lipid production of oleaginous yeasts and a similar strategy might be used in other oleaginous microbes.

TiO2-modified CNx nanowires as a Pt electrocatalyst support with high activity and durability for the oxygen reduction reaction.

A Pt/TiO2-modified carbon nitride nanofiber (Pt/TiO2-CNx) catalyst has been synthesized by a chemical method for the oxygen reduction reaction (ORR). The material characteristics confirmed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) have indicated that the TiO2-CNx nanowires have a diameter of about 35-85 nm, the TiO2 nanoparticles are embedded in CNx nanowires and Pt nanoparticles are about 2.21 nm in size. The X-ray photoelectron spectra (XPS) show that Ti has a shift in the binding energy of Ti 2p, implying suboxide formation. Pt/0.2 g TiO2-CNx has about 3% loss in the (electrochemical surface area) ESA after 1000 cycles, however, the Pt/C catalyst has about 50.8% loss in the ESA. Pt/0.2 g TiO2-CNx has much better activity than Pt/C, which is proposed to be due to the high total surface area of Pt. The durability test shows that the Pt/0.2 g TiO2-CNx catalyst has no loss of activity after 5000 cycles. After 5000 cycles, the average size of Pt nanoparticles and the peaks of Pt 4f almost remain unchanged. The high durability of Pt/0.2 g TiO2-CNx is attributed to the corrosion-resistance of 0.2 g TiO2-CNx nanowires support and the good interaction between the 0.2 g TiO2-CNx support and the Pt nanoparticles.