Studies on Bioethanol Production from Cellulosic Waste by Recombinant Saccharomyces
Date Issued
2010
Date
2010
Author(s)
Ying Su, Mei
Abstract
Production of biofuel from biomass is one way to reduce both consumption of fossil fuels and environmental pollution. Bioethanol is appropriate for the fuel blends because of its reduction of CO2 and exhaust greenhouse gas emission from the transport sector. Large-scale lignocellulosic biomass types are the most promising feedstock considering its high yields, low costs, and low environmental impacts. Whole feedstock utilization is one of the primaries to make lignocellulosic ethanol processes economically competitive. Recently, biotechnological fermentation process is generally satisfied in worldwide demand of ethanol, and therefore ethanol producing organisms have been developed for commercial processes, but its narrow scope of fermentable carbohydrates has limited its industrial exploitation. The current available technology, which is the engineered microorganisms must ferment all lignocellulosic derived monosaccharides, including hexose and pentose sugars to ethanol. The improved conversion efficiency of ethanol production is based on utilization of a pentose present in hemicellulose, a ubiquitous component of lignocellulosic biomass. This study evaluate the feasibility of using sorghum liquor waste for bioethanol production, we serially investigated the effectiveness of physical treatment, microwave irradiation pretreatment, enzymatic hydrolysis, and fermentation. Composition analysis revealed that Kinmen sorghum liquor waste (KS) and Chiayi sorghum liquor waste (CS) contain approximately 17.2 ± 0.7% and 18.2 ± 0.6% cellulose, 19.0 ± 0.6% and 21.6 ± 1.0% hemicellulose, 18.5 ± 0.8% and 20.6 ± 1.7% acid detergent lignin, and 22.1 ± 0.7% and 23.3 ± 0.4% starch, respectively, on dry weight basis. The reducing sugar yield obtained after microwave irradiation pretreatment and enzymatic hydrolysis of KS and CS were 331.1 and 341.3 mg/g dry weight. The ethanol yields obtained after fermentation of KS and CS hydrolysates with S. cerevisiae were 0.13 and 0.14 g/g dry weight, respectively. This operation of pretreatment may provide a suggestible pattern of utilizing feedstock that contain lignocellulose and starch for ethanolic fermentation. Furthermore, the fermentation performance of the pentose fermenting S. cerevisiae strains in lignocellulose hydrolysate is designed. Through construction of the integrating vectors by employ strong promoter ADH1 and inducible promoter GAL1 to regulate the expression of heterogeneous XYL1, XYL2 and XYL3 genes in recombinant S. cerevisiae. The resulting strains exhibited xylose reductase (XR), xylitol dehydrogenase (XDH), and xylulokinase (XK) activities in a defined mineral medium containing CS hydrolysate and a higher theoretical ethanol yield approximately 80.7 and 85.5% than that obtained by the parental strain YPH499. The recombinant strain PSC207 overexpression of the heterogeneous genes from P. stipitis CBS6045 resulted in the produced less xylitol (0.25 g xylitol/g xylose) but consumption of more xylose than strain PSC107, which carries XYL3 from S. cerevisiae CBS8066. PsXYL3 is a better target for overexpression than ScXYL3 for engineering S. cerevisiae strains capable of fermenting non-detoxified CS hydrolysate.
Subjects
Bioethanol
Sorghum liquor waste
microwave irradiation pretreatment
recombinant Saccharomyces cerevisiae
Pichia stipitis
SDGs
Type
thesis
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