Enantiocomplementary Yarrowia lipolytica Oxidoreductases: Alcohol Dehydrogenase 2 and Short Chain Dehydrogenase/Reductase

Validated Growth Rate-Dependent Regulation of Lipid Metabolism in Yarrowia lipolytica

Given the strong potential of Yarrowia lipolytica to produce lipids for use as renewable fuels and oleochemicals, it is important to gain in-depth understanding of the molecular mechanism underlying its lipid accumulation. As cellular growth rate affects biomass lipid content, we performed a comparative proteomic analysis of Y. lipolytica grown in nitrogen-limited chemostat cultures at different dilution rates. After confirming the correlation between growth rate and lipid accumulation, we were able to identify various cellular functions and biological mechanisms involved in oleaginousness. Inspection of significantly up- and downregulated proteins revealed nonintuitive processes associated with lipid accumulation in this yeast. This included proteins related to endoplasmic reticulum (ER) stress, ER–plasma membrane tether proteins, and arginase. Genetic engineering of selected targets validated that some genes indeed affected lipid accumulation. They were able to increase lipid content and were complementary to other genetic engineering strategies to optimize lipid yield.

Enantioselective synthesis of enantiopure chiral alcohols using carbonyl reductases screened from Yarrowia lipolytica

AIMS

We aimed to explore Yarrowia lipolytica carbonyl reductases as effective biocatalysts and to develop efficient asymmetric reduction systems for chiral alcohol synthesis.

METHODS AND RESULTS

Yarrowia lipolytica carbonyl reductase genes were obtained via homologous sequence amplification strategy. Two carbonyl reductases, YaCRI and YaCRII, were identified and characterized, and used to catalyse the conversion of 2-hydroxyacetophenone (2-HAP) to optically pure (S)-1-phenyl-1,2-ethanediol. Enzymatic assays revealed that YaCRI and YaCRII exhibited specific activities of 6·96 U mg^-1 (99·8% e.e.) and 7·85 U mg^-1 (99·9% e.e.), respectively, and showed moderate heat resistance at 40-50°C and acid tolerance at pH 5·0-6·0. An efficient whole-cell two-phase system was established using reductase-expressing recombinant Escherichia coli. The conversion of 2-HAP (20·0 g l^-1 ) conversion with the solvent of dibutyl phthalate was approximately 70-fold higher than in water. Furthermore, the two recombinant E. coli displayed biocatalyst activity and enantioselectivity towards several different carbonyl compounds, and E. coli BL21 (DE3)/pET-28a-yacrII showed a broad substrate spectrum.

CONCLUSIONS

A new whole-cell recombinant E. coli-based bioreduction system for enantiopure alcohol synthesis with high enantioselectivity at high substrate concentrations was developed.

SIGNIFICANCE AND IMPACT OF THE STUDY

We proposed a promising approach for the efficient preparation of enantiopure chiral alcohols.

Three alcohol dehydrogenase genes and one acetyl-CoA synthetase gene are responsible for ethanol utilization in Yarrowia lipolytica

The non-conventional yeast Yarrowia lipolytica is able to utilize a wide range of different substrates like glucose, glycerol, ethanol, acetate, proteins and various hydrophobic molecules. Although most metabolic pathways for the utilization of these substrates have been clarified by now, it was not clear whether ethanol is oxidized by alcohol dehydrogenases or by an alternative oxidation system inside the cell. In order to detect the genes that are required for ethanol utilization in Y. lipolytica, eight alcohol dehydrogenase (ADH) genes and one alcohol oxidase gene (FAO1) have been identified and respective deletion strains were tested for their ability to metabolize ethanol. As a result of this, we found that the availability of ADH1, ADH2 or ADH3 is required for ethanol utilization in Y. lipolytica. A strain with deletions in all three genes is lacking the ability to utilize ethanol as sole carbon source. Although Adh2p showed by far the highest enzyme activity in an in vitro assay, the availability of any of the three genes was sufficient to enable a decent growth. In addition to ADH1, ADH2 and ADH3, an acetyl-CoA synthetase encoding gene (ACS1) was found to be essential for ethanol utilization. As Y. lipolytica is a non-fermenting yeast, it is neither able to grow under anaerobic conditions nor to produce ethanol. To investigate whether Y. lipolytica may produce ethanol, the key genes of alcoholic fermentation in S. cerevisiae, ScADH1 and ScPDC1, were overexpressed in an ADH and an ACS1 deletion strain. However, instead of producing ethanol, the respective strains regained the ability to use ethanol as single carbon source and were still not able to grow under anaerobic conditions.