Effects of Medium Components on Isocitric Acid Production by Yarrowia lipolytica Yeast

The microbiological production of isocitric acid (ICA) is more preferable for its application in medicine and food, because the resulting product contains only the natural isomer—threo-DS. The aim of the present work was to study ICA production by yeast using sunflower oil as carbon source. 30 taxonomically different yeast strains were assessed for their capability for ICA production, and Y. lipolytica VKM Y-2373 was selected as a promising producer. It was found that ICA production required: the limitation of Y. lipolytica growth by nitrogen, phosphorus, sulfur or magnesium, and an addition of iron, activating aconitate hydratase, a key enzyme of isocitrate synthesis. Another regulatory approach capable to shift acid formation to a predominant ICA synthesis is the use of inhibitors (itaconic and oxalic acids), which blocks the conversion of isocitrate at the level of isocitrate lyase. It is recommended to cultivate Y. lipolytica VKM Y-2373 under nitrogen deficiency conditions with addition of 1.5 mg/L iron and 30 mM itaconic acid. Such optimized nutrition medium provides 70.6 g/L ICA with a ratio between ICA and citric acid (CA) equal 4:1, a mass yield (YICA) of 1.25 g/g and volume productivity (QICA) of 1.19 g/L·h.