Improved Xylose Consumption through Saccharomyces cerevisiae Strain Evolution

Lignocellulose hydrolyzates are difficult substrates for ethanol production due to its high resistance to inhibitors during pretreatment and hydrolysis. In addition, efficient utilization of hexose and pentose sugars poses difficulty for the development of Saccharomyces cerevisiae strains for biomass-to-ethanol processes. Metabolic engineering and laboratory evolution have been utilized to produce desired strain properties.

Two descendants, strains IBB10A02 and IBB10B05, were evolved from S. cerevisiae strain BP10001. The strains were obtained by a two-step laboratory evolution. The IBB10A02 strain was selected for fast xylose fermentation with anaerobic growth before adaption while the IBB10B05 strain was selected for fast xylose fermentation with anaerobic growth after adaption. Enzymatic hydrolyzates were prepared from up to 15% dry mass pretreated wheat straw. In all strains, yield coefficients based on total sugar consumed were high for ethanol and notably low for fermentation by-products. The xylose consumption rate was also enhanced , compared to the non-evolved strain BP10001. Under the conditions used, IBB10B05 was also capable of slow anaerobic growth.

Laboratory evolution of strain BP10001 resulted in enhanced xylose at almost complete retention of the fermentation capabilities previously acquired through metabolic engineering. The new strain IBB10B05 is a good candidate for intensification of lignocellulose-to-bioethanol processes.