Analysis Of Bioethanol Production From Glucose-xylose Co-fermentation By Engineered Saccharomyces Cerevisiae Using Distinct Lignocellulose

Lignocellulose represents the most abundant biomass resource for biofuels and biochemical on the earth.Importantly,lignocellulose ethanol has been examined as an excellent additive to the gasoline.In principle,lignocellulose consists of two major sugars（glucose and xylose,）,which are respectively derived from cellulose and hemicelluloses.As the traditional fermentation yeast strain,such as Saccharomyces cerevisiae,can not use xylose as carbon source for bioethanol production,genetic engineering technology has been applied by introducing exogenous genes into yeast strain,but little is reported about how to combine the transgenic Saccharomyces cerevisiae strain and distinct lignocellulose materials for high bioethanol production under mild physical and chemical pretreatment.In our previous studies,we selected transgenic S.cerevisiae strains（SF4 and E4）that integrated three distinct enzymes by over-expressing exogenous xylose reductase,xylitol dehydrogenase and xylulokinase genes.In this study,we used SF4 and E4 strains to perform ethanol fermentation using total glucose and xylose released from enzymatic hydrolysis after pretreatments with Miscanthus and wheat biomass residues.The major results were described below:1.Compared to the wild type strain that only use hexoses as carbon source,the SF4and E4 strains could grow well on the culture medium containing xylose as only carbon source.2.As a comparison between 1%H₂SO₄ and 2%NaOH pretreatments in Miscanthus accession（Msi07）,the S.cerevisiae wild type had bioethanol yields from 6.27%（1%H₂SO₄）to 8.38%（2%NaOH）,the transgenic SF4 strain showed the ethanol yields from6.76%to 8.80%and the E4 strain was from 6.29%to 9.23%.Using another Miscanthus accession（VI-A-3）,the wild type strain showed the ethanol yields from 5.78%to 8.54%,SF4 was from 5.87%to 9.26%and E4 was from 5.96%to 9.36%.3.Using total hexoses and xylose released from enzymatic hydrolysis after 4%NaOH pretreatment with Miscanthus accession（VI-A-3）,the transgenic yeast strains showed much increased bioethanol yield rate by 25.69%,compared to the wild type strain.4.Using total hexoses and xylose released from enzymatic hydrolysis after 1%NaOH pretreatments with the steam-exploded Miscanthus and wheat residues,the transgenic E4strain showed the highest bioethanol yield of Miscanthus at 20.61%（%dry matter）,and the SF4 strain had the highest bioethanol yield of wheat at 20.32%,compared to the previous reports in Miscanthus and wheat.