| Cellulosic ethanol catches more and more attention in recent years.Much research have been done to improve glucose and xylose utilization efficiency in lignocellulosic hydrolysate,especially the ability of xylose-utilizing and the simultaneous utilization of xylose and glucose in Saccharomyces cerevisiae.Preliminary simultaneous utilization of xylose and glucose was realized by RPE1 deletion in our previous research.But due to the limitation of the pentose phosphate pathway metabolic flow,the ratio of the simultaneous utilized xylose was too low to meet the requirements of industrial production of cellulosic ethanol.This study focused on the regulation of glucose metabolism.By means of molecular biology,we regulated the key enzymes in EMP and PP pathways.By overexpression of ZWF1 with plasmid vector to enhance pentose phosphate pathway,and EMP pathway was weakened by replacement of PGI1 p with other promoters.The transcription of ZWF1 enhanced 130 times by overexpression it in multi-copy plasmid pRS425 K with strong promoter TDH1 p and the corresponding G6 PDH activitie increased by 30 times.The glucose and xylose consumption rate increased by 80% and 72% in SyBE_Sc122001 in which ZWF1 was overexpressed with TPI1 p in pRS425 K.The ethanol yields did not improve in ZWF1 overexpression strains,but decreased slightly on the contrary.In the strain with replacement PGI1 p by PDA1 p,the PGI activity decreased by 80% and the co-utilized xylose increased by 16.3%.The ethanol yield increased in all of the PGI1 down-regulation strains.By dual modulation of ZWF1 and PGI1 in the strain SyBE_Sc17004,the glucose consumption rate improved further,but the co-utilized xylose was inferior to the strain that overexpression ZWF1 alone.Expression the fused genes of ZWF1 and HXK2 resulted in the decrease in the glucose consumption rate and enhancement in xylose consumption.By deleting HXK1 or HXK2,both the glucose and xylose consumption rates slowed down. |
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