Characterization of High Ethanol Producing Properties of Recombinant Saccharomyces Cerevisiae ETS3 Transformed with a Mutated SPT15 Gene

Osmotic stress caused by high sugar and ethanol concentrations is one of the major reasons for reduction of bioethanol productivity during yeast fermentation. To overcome this hurdle, global transcription machinery engineering (gTME) by introducing SPT15 variants encoding S. cerevisiae TATA-binding proteins was applied and S. cerevisiae ETS3 was selected to possess enhanced ethanol producing ability under high osmotic pressure. In this study, its fermentation properties were evaluated in batch and fed-batch cultures using various glucose concentration under different aeration conditions. A batch culture of ETS3 with 300 g/L glucose at oxygen-limited condition resulted in 22.2 g/L dry cell mass, 98.1 g/L ethanol concentration and 1.82 g/L-h ethanol productivity which were about 13–16% increases relative to those of the S. cerevisiae BY4741 host strain. A micro-aerobic condition elevated ethanol productivity to 2.49 g/L-h without significant changes of other fermentation parameters. In a fed-batch fermentation with 400 g/L glucose, ETS3 produced up to 151.7 g/L ethanol with a maximum ethanol yield of 0.402 g/g and showed a 23% increase in dry cell mass and 16% increases in ethanol concentration and productivity in comparison to the host strain. Considering the enhanced ethanol production performances of ETS3 regardless of oxygen content, it is obvious that gTME is an effective tool to gain a robust S. cerevisiae strain against high osmotic pressure.