Ethanol production from cellulosic materials using cellulase-expressing yeast.

Area of Science:

• Biotechnology
• Synthetic Biology
• Biochemical Engineering

Background:

• Cellulose, a major component of plant biomass, is a promising renewable feedstock for biofuel production.
• Efficient conversion of cellulose to ethanol requires effective enzymatic hydrolysis and subsequent fermentation.
• Current methods often involve separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF), which can be inefficient.

Purpose of the Study:

• To engineer Saccharomyces cerevisiae for direct ethanol fermentation from amorphous cellulose.
• To evaluate the efficacy of cell surface display versus secretion for cellulase enzymes in direct fermentation.
• To enhance cellulose degradation and ethanol yield through co-expression of key cellulases.

Main Methods:

• Genomic integration of endoglucanase (EG), cellobiohydrolase (CBH), and beta-glucosidase (BGL) genes from Trichoderma reesei and Aspergillus aculeatus into Saccharomyces cerevisiae MT8-1.
• Cell surface display and secretion of EG, CBH, and BGL enzymes.
• Enzyme activity assays and cellulose degradation measurements.
• Direct ethanol fermentation experiments using phosphoric acid swollen cellulose (PASC) as feedstock.

Main Results:

• Successful expression and activity of displayed and secreted cellulase enzymes.
• Co-expression of EG and CBH increased cellulose degradation by 3- to 5-fold.
• Direct ethanol fermentation using yeast with displayed EG, CBH, and BGL yielded 2.1 g/L ethanol.
• Displayed enzyme systems achieved higher ethanol yields compared to secreted enzyme systems (1.6 g/L ethanol).

Conclusions:

• Cell surface display of cellulase enzymes in yeast is a viable strategy for direct ethanol fermentation from cellulose.
• This approach enhances cellulose degradation efficiency.
• Cell surface display is more suitable than enzyme secretion for direct cellulosic ethanol production.