Albany 2015:Book of Abstracts
June 9-13 2015
©Adenine Press (2012)
Metabolism of Biodiesel-derived Waste in the Yeast Yarrowia lipolytica – Producers of Citric- and Isocitric Acids
The biodiesel-derived waste (BDW) presents the two substrate pairs - 65% of glycerol and 20% of fatty acids. In this study, the metabolic pathways of BDW utilization in Yarrowia lipolytica yeast – producers of citric- and isocitric acids were studied by a comparison of growth dynamics, the consumption of glycerol and fatty acids, as well as by measuring the activity of the enzymes involved in the glycerol- and fatty acids metabolism. It was shown that the glycerol and fatty acids do not suppress the metabolism of each other and consumed simultaneously by Y. lipolytica. The key enzymes of glycerol metabolism - glycerol kinase (GK) and the glyoxylate cycle responsible for the metabolism of fatty acids - isocitrate lyase (IL) and malate synthase (MS) are induced at the beginning of the growth of Y. lipolytica and remain active during whole cultivation. The active functioning of the glyoxylate cycle upon the assimilation of BDW is confirmed by the high activities of citrate synthase (CS) and aconitate hydratase (AH), which operate both in the glyoxylate cycle and in the tricarboxylic acid cycle of yeast. For comparison, NAD- and NADP-dependent isocitrate dehydrogenases (NAD-ICDH and NADP-ICDH), which are not involved in the glyoxylate cycle were at low level (Table). It should be noted that the simultaneous utilization of two different substrates is not typical of microorganisms, which first assimilate one the two available substrates (commonly, a carbohydrate), whereas the assimilation of the other substrate starts only after the first substrate is fully consumed from the medium. In the literature there are data that the different sugars produce signals which modify the conformation of certain proteins that, in turn, directly or through a regulatory cascade affect the expression of the genes subject to catabolite repression. These genes are not all controlled by a single set of regulatory proteins (Cho et al. 2009). Based on the activities of enzymes involved of the tricarboxylic acid cycle and the glyoxylate cycle it will be explained the differences between the citric- and isocitric acids production by wild and mutant strains of Y. lipolytica yeasts.
This work was supported by the Russian Foundation for Basic Research (grant no. 13-08-00060).