Overexpression of the genes PDC1 and ADH1 activates glycerol conversion to ethanol in the thermotolerant yeast Ogataea (Hansenula) polymorpha

Conversion of byproduct from biodiesel production glycerol to high-value compounds is of great importance. Ethanol is considered a promising product of glycerol bioconversion. The methylotrophic thermotolerant yeast Ogataea (Hansenula) polymorpha is of great interest for this purpose as the glycerol byproduct contains methanol and heavy metals as contaminants, and this yeast utilizes methanol and is relatively resistant to heavy metals. Besides, O. polymorpha shows robust growth on glycerol and produces ethanol from various carbon sources. The thermotolerance of this yeast is an additional advantage, allowing increased fermentation temperature to 45-48 degrees C, leading to increased rate of the fermentation process and a fall in the cost of distillation. The wild-type strain of O. polymorpha produces insignificant amounts of ethanol from glycerol (0.8g/l). Overexpression of PDC1 coding for pyruvate decarboxylase enhanced ethanol production up to 3.1g/l, whereas simultaneous overexpression of PDC1 and ADH1 (coding for alcohol dehydrogenase) led to further increase in ethanol production from glycerol. Moreover, the increased temperature of fermentation up to 45 degrees C stimulated the production of ethanol from glycerol used as the only carbon source up to 5.0g/l, which exceeds the data obtained by methylotrophic yeast strains reported so far. Copyright (c) 2016 John Wiley & Sons, Ltd.