Intracellular expression of Vitreoscilla haemoglobin improves lipid production in Yarrowia lipolytica

Genetic modification by overexpressing Vitreoscilla haemoglobin (VHb) is an efficient and economic method for improving O-2 utilization for microbial fermentation. In this study, VHb was expressed in oleaginous yeast, Yarrowia lipolytica, and its effect on lipid accumulation was analysed. During fermentation, the dissolved oxygen (DO) concentration was controlled at 5, 10, 20 and 30 of full O-2 saturation and also uncontrolled by varying the stirring speed and aeration rate. Yarrowia lipolytica harbouring the VHb gene (VHb(+) strain) displayed more pseudomycelium than the control strain (VHb(-) strain), and VHb expression also enhanced the cell density. When DO level was controlled at 30%, the biomass of VHb(+) strains reached about 19 g l(-1) and increased by 27% compared to VHb(-) strains. Total fatty acid contents, although, were higher in VHb(+) strains than in VHb(-) strains under all DO levels, and maximally increased by c. 40% (from 10 center dot 5 to 14 center dot 5% of the biomass) when the DO concentration was controlled at 30%. VHb overexpression, however, markedly suppressed citrate secretion. In addition, expression of VHb also induced significant changes in fatty acid composition and increased the oleic acid content.