title: Functional overexpression of genes involved in erythritol synthesis in the yeastYarrowia lipolytica.
abstract: BACKGROUND
  Erythritol, a four-carbon polyol synthesized by microorganisms as an osmoprotectant, is a natural sweetener produced on an industrial scale for decades. Despite the fact that the yeastYarrowia lipolyticahas been reported since the 1970s as an erythritol producer, the metabolic pathway of this polyol has never been characterized. It was shown that erythritol synthesis in yeast occurs via the pentose phosphate pathway (PPP). The oleaginous yeastY. lipolyticais a good host for converting inexpensive glycerol into a value-added product such as erythritol. Glycerol is a renewable feedstock which is produced on a large scale as a waste product by many branches of industry.
  
  
  RESULTS
  In this study, we functionally overexpressed four genes involved in the pentose phosphate pathway (PPP): geneYALI0E06479g encoding transketolase (TKL1), geneYALI0F15587g encoding transaldolase (TAL1), geneYALI0E22649g encoding glucose-6-phosphate dehydrogenase (ZWF1), and geneYALI0B15598g encoding 6-phosphogluconate dehydrogenase (GND1). Here, we show that the crucial gene for erythritol synthesis inY. lipolyticais transketolase. Overexpression of this gene results in a twofold improvement in erythritol synthesis during a shake-flask experiment (58 g/L). Moreover, overexpression ofTKL1allows for efficient production of erythritol independently from the supplied dissolved oxygen. Fermentation conducted in a 5-L bioreactor at low agitation results in almost 70% higher titer of erythritol over the control strain.
  
  
  CONCLUSIONS
  This work presents the importance of the PPP in erythritol synthesis and the feasibility for economic production of erythritol from glycerol by the yeastY. lipolytica.
authors.affiliation: Department of Biotechnology and Food Microbiology, Wroclaw University of Environmental and Life Sciences, Chełmońskiego 37, 51-630 Wrocław, Poland.
authors.forename: Aleksandra M
authors.identifier: 0000-0003-1604-1635
authors.initials: AM
authors.lastname: Mirończuk
authors.affiliation: Department of Biotechnology and Food Microbiology, Wroclaw University of Environmental and Life Sciences, Chełmońskiego 37, 51-630 Wrocław, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Biegalska
authors.affiliation: Department of Biotechnology and Food Microbiology, Wroclaw University of Environmental and Life Sciences, Chełmońskiego 37, 51-630 Wrocław, Poland.
authors.forename: Adam
authors.initials: A
authors.lastname: Dobrowolski
keywords: Erythritol; Glycerol; Pentose phosphate pathway; Transketolase; Yarrowia lipolytica