Background
Dwindling supplies of petroleum and growing environmental
concerns over its use has led to increasing interest
in developing biomass as a feedstock for liquid fuels.
In particular, bioethanol produced from biomass represents
a promising alternative fuel or gasoline extender.
Currently, the main feedstock for bioethanol production
is starch-rich biomass, as it is rapidly hydrolyzed by
amylases, giving high yields of glucose. However, lignocellulosic
biomass (such as rice straw, which is one of
the most abundant lignocellulosic waste materials), is
regarded as a promising starting material for bioethanol
production, because it is abundant, inexpensive, renewable
and has favorable environmental properties [1]. Despite
these advantages, lignocellulosic biomass is much more
expensive to process than grains because of the need for
extensive pretreatment and relatively large amounts of cellulases
for efficient hydrolysis [1]. Therefore, efficient and
cost-effective methods for the degradation and fermentation
of lignocellulosic biomass to ethanol are required.
The efficient degradation of lignocellulosic biomass
requires the synergistic action of the cellulolytic
enzymes endoglucanase (EG), cellobiohydrolase (CBH)
and b-glucosidase (BGL), and some hemicellulolytic
enzymes. Although there are numerous reports of
lower-cost ethanol production from cellulosic material
by consolidating hydrolyzing and fermentation steps
using recombinant Saccharomyces cerevisiae strains
expressing cellulolytic enzymes [2-5], the efficiency of
BackgroundDwindling supplies of petroleum and growing environmentalconcerns over its use has led to increasing interestin developing biomass as a feedstock for liquid fuels.In particular, bioethanol produced from biomass representsa promising alternative fuel or gasoline extender.Currently, the main feedstock for bioethanol productionis starch-rich biomass, as it is rapidly hydrolyzed byamylases, giving high yields of glucose. However, lignocellulosicbiomass (such as rice straw, which is one ofthe most abundant lignocellulosic waste materials), isregarded as a promising starting material for bioethanolproduction, because it is abundant, inexpensive, renewableand has favorable environmental properties [1]. Despitethese advantages, lignocellulosic biomass is much moreexpensive to process than grains because of the need forextensive pretreatment and relatively large amounts of cellulasesfor efficient hydrolysis [1]. Therefore, efficient andcost-effective methods for the degradation and fermentationof lignocellulosic biomass to ethanol are required.The efficient degradation of lignocellulosic biomassrequires the synergistic action of the cellulolyticenzymes endoglucanase (EG), cellobiohydrolase (CBH)and b-glucosidase (BGL), and some hemicellulolyticenzymes. Although there are numerous reports oflower-cost ethanol production from cellulosic materialby consolidating hydrolyzing and fermentation stepsusing recombinant Saccharomyces cerevisiae strains
expressing cellulolytic enzymes [2-5], the efficiency of
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