The growth of Yarrowia lipolytica on glycerol was studied in bioreactor repeated batch cultures and three distinct phases, namely biomass production phase, lipogenic phase and citric acid production phase were identified during growth cycle. In each phase, yeast cells were characterised by specific morphological and biochemical features. Though high activity of NAD(+) dependent iso-citric dehydrogenase (NAD(+)-ICDH) was detected during biomass production phase, this activity was significantly decreased afterwards inducing lipogenesis. A further drop in NAD(+)-ICDH activity to minimal levels and a decrease in glycerol kinase activity were observed during the citric acid production phase. Surprisingly, citric acid production was accompanied by storage (neutral) lipid turnover, along with remarkable biosynthesis of glycolipids, sphingolipids and phospholipids. Oleic acid was the major fatty acid in all lipid fractions and phosphatidylcholine was the main phospholipid. This study allows concluding that Y. lipolytica successfully converts glycerol via phosphorylation pathway into valuable biotechnological products, such as single cell oil and citric acid.
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