The conversion of biomass into fuel ethanol has received considerable interest in recent years. Starchy and cellulosic substrates are the most abundant biomass resources. Bioethanol has already been produced from sugar cane and starch rich grains in Brazil and the United States. Even though the process of converting starchy substrates into ethanol is a fairly mature technology, the methods are still very expensive and the development of a Consolidated Bioprocessing through amylolytic yeast could lead to considerable cost reductions. This study aimed to construct an efficient amylolytic Saccharomyces cerevisiae strain for the industrial ethanol production from starchy feedstocks. Several fungal amylolytic genes were screened for their high expression into the laboratory strain S. cerevisiae Y294. The most proficient sequences were then selected to be integrated into natural yeasts previously evaluated for their fermentative traits and robustness suitable for the industrial scale bioethanol production. A codon-optimised sgaI gene encoding a fungal glucoamylase was introduced into the chromosomal δ-sequences of wild type S. cerevisiae strains. The obtained integrants, mitotically stable after 240 generations in non selective broth, showed high glucoamylase activities both on soluble and raw starch. During anaerobic cultivation, the strains produced a 79% of theoretical maximum ethanol yield from soluble starch. On raw starch, the recombinant strains exhibited improvable fermentative performance with an ethanol yield corresponding to 75% of the theoretical maximum. On the basis of the preliminary fermentation studies, the engineered yeasts could be promising for the Consolidated Bioprocessing of starchy substrates such as corn, wheat and many industrial residues (cereal brans, potato peels and spent brewers’ grains). The co-expression in the recombinant strains of sgaI and other selected amylolytic gene sequences is in progress towards the development of an efficient starch-converting CBP yeast.
Towards the Consolidated bioprocessing of starchy materials for industrial bioethanol production
FAVARO, LORENZO;BASAGLIA, MARINA;TRENTO, ALBERTO;CASELLA, SERGIO
2011
Abstract
The conversion of biomass into fuel ethanol has received considerable interest in recent years. Starchy and cellulosic substrates are the most abundant biomass resources. Bioethanol has already been produced from sugar cane and starch rich grains in Brazil and the United States. Even though the process of converting starchy substrates into ethanol is a fairly mature technology, the methods are still very expensive and the development of a Consolidated Bioprocessing through amylolytic yeast could lead to considerable cost reductions. This study aimed to construct an efficient amylolytic Saccharomyces cerevisiae strain for the industrial ethanol production from starchy feedstocks. Several fungal amylolytic genes were screened for their high expression into the laboratory strain S. cerevisiae Y294. The most proficient sequences were then selected to be integrated into natural yeasts previously evaluated for their fermentative traits and robustness suitable for the industrial scale bioethanol production. A codon-optimised sgaI gene encoding a fungal glucoamylase was introduced into the chromosomal δ-sequences of wild type S. cerevisiae strains. The obtained integrants, mitotically stable after 240 generations in non selective broth, showed high glucoamylase activities both on soluble and raw starch. During anaerobic cultivation, the strains produced a 79% of theoretical maximum ethanol yield from soluble starch. On raw starch, the recombinant strains exhibited improvable fermentative performance with an ethanol yield corresponding to 75% of the theoretical maximum. On the basis of the preliminary fermentation studies, the engineered yeasts could be promising for the Consolidated Bioprocessing of starchy substrates such as corn, wheat and many industrial residues (cereal brans, potato peels and spent brewers’ grains). The co-expression in the recombinant strains of sgaI and other selected amylolytic gene sequences is in progress towards the development of an efficient starch-converting CBP yeast.
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