Limits...
Cellulosic ethanol production using a yeast consortium displaying a minicellulosome and β-glucosidase.

Kim S, Baek SH, Lee K, Hahn JS - Microb. Cell Fact. (2013)

Bottom Line: Consolidated bioprocessing (CBP), combining cellulase production, saccharification, and fermentation into one step, has been proposed as the most efficient way to reduce the production cost of cellulosic bioethanol.On the other hand, BGLI was independently assembled to the cell surface since we newly found that it already has a cell adhesion characteristic.A mixture of cells with the optimized mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 produced 1.80 g/l ethanol after 94 h, indicating about 20% increase compared with a consortium composed of an equal amount of each cell type (1.48 g/l).

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Chemical and Biological Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea.

ABSTRACT

Background: Cellulosic biomass is considered as a promising alternative to fossil fuels, but its recalcitrant nature and high cost of cellulase are the major obstacles to utilize this material. Consolidated bioprocessing (CBP), combining cellulase production, saccharification, and fermentation into one step, has been proposed as the most efficient way to reduce the production cost of cellulosic bioethanol. In this study, we developed a cellulolytic yeast consortium for CBP, based on the surface display of cellulosome structure, mimicking the cellulolytic bacterium, Clostridium thermocellum.

Results: We designed a cellulolytic yeast consortium composed of four different yeast strains capable of either displaying a scaffoldin (mini CipA) containing three cohesin domains derived from C. thermocellum, or secreting one of the three types of cellulases, C. thermocellum CelA (endoglucanase) containing its own dockerin, Trichoderma reesei CBHII (exoglucanase) fused with an exogenous dockerin from C. thermocellum, or Aspergillus aculeatus BGLI (β-glucosidase). The secreted dockerin-containing enzymes, CelA and CBHI, were randomly assembled to the surface-displayed mini CipA via cohesin-dockerin interactions. On the other hand, BGLI was independently assembled to the cell surface since we newly found that it already has a cell adhesion characteristic. We optimized the cellulosome activity and ethanol production by controlling the combination ratio among the four yeast strains. A mixture of cells with the optimized mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 produced 1.80 g/l ethanol after 94 h, indicating about 20% increase compared with a consortium composed of an equal amount of each cell type (1.48 g/l).

Conclusions: We produced cellulosic ethanol using a cellulolytic yeast consortium, which is composed of cells displaying mini cellulosomes generated via random assembly of CelA and CBHII to a mini CipA, and cells displaying BGLI independently. One of the advantages of this system is that ethanol production can be easily optimized by simply changing the combination ratio of the different populations. In addition, there is no limitation on the number of enzymes to be incorporated into this cellulosome structure. Not only cellulases used in this study, but also any other enzymes, including cellulases and hemicellulases, could be applied just by fusing dockerin domains to the enzymes.

Show MeSH

Related in: MedlinePlus

Direct fermentation of amorphous cellulose to ethanol. Time course of ethanol production from a yeast consortium composed of the mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 (optimized ratio, closed circle) or 1:1:1:1 (equal ratio, open circle), or EBY100 cells containing pCT-mini CipA (control, open triangle).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3585817&req=5

Figure 4: Direct fermentation of amorphous cellulose to ethanol. Time course of ethanol production from a yeast consortium composed of the mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 (optimized ratio, closed circle) or 1:1:1:1 (equal ratio, open circle), or EBY100 cells containing pCT-mini CipA (control, open triangle).

Mentions: The ability of direct ethanol fermentation from PASC was examined using a mixture of cells composed of the optimized ratio and an equal amount of each cell type. The maximum ethanol production was 1.80 g/l after 94 h in a consortium of the optimized ratio, which indicated about 20% increase compared with a consortium composed of an equal ratio (1.48 g/l) (Figure 4).


Cellulosic ethanol production using a yeast consortium displaying a minicellulosome and β-glucosidase.

Kim S, Baek SH, Lee K, Hahn JS - Microb. Cell Fact. (2013)

Direct fermentation of amorphous cellulose to ethanol. Time course of ethanol production from a yeast consortium composed of the mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 (optimized ratio, closed circle) or 1:1:1:1 (equal ratio, open circle), or EBY100 cells containing pCT-mini CipA (control, open triangle).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585817&req=5

Figure 4: Direct fermentation of amorphous cellulose to ethanol. Time course of ethanol production from a yeast consortium composed of the mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 (optimized ratio, closed circle) or 1:1:1:1 (equal ratio, open circle), or EBY100 cells containing pCT-mini CipA (control, open triangle).
Mentions: The ability of direct ethanol fermentation from PASC was examined using a mixture of cells composed of the optimized ratio and an equal amount of each cell type. The maximum ethanol production was 1.80 g/l after 94 h in a consortium of the optimized ratio, which indicated about 20% increase compared with a consortium composed of an equal ratio (1.48 g/l) (Figure 4).

Bottom Line: Consolidated bioprocessing (CBP), combining cellulase production, saccharification, and fermentation into one step, has been proposed as the most efficient way to reduce the production cost of cellulosic bioethanol.On the other hand, BGLI was independently assembled to the cell surface since we newly found that it already has a cell adhesion characteristic.A mixture of cells with the optimized mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 produced 1.80 g/l ethanol after 94 h, indicating about 20% increase compared with a consortium composed of an equal amount of each cell type (1.48 g/l).

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Chemical and Biological Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Republic of Korea.

ABSTRACT

Background: Cellulosic biomass is considered as a promising alternative to fossil fuels, but its recalcitrant nature and high cost of cellulase are the major obstacles to utilize this material. Consolidated bioprocessing (CBP), combining cellulase production, saccharification, and fermentation into one step, has been proposed as the most efficient way to reduce the production cost of cellulosic bioethanol. In this study, we developed a cellulolytic yeast consortium for CBP, based on the surface display of cellulosome structure, mimicking the cellulolytic bacterium, Clostridium thermocellum.

Results: We designed a cellulolytic yeast consortium composed of four different yeast strains capable of either displaying a scaffoldin (mini CipA) containing three cohesin domains derived from C. thermocellum, or secreting one of the three types of cellulases, C. thermocellum CelA (endoglucanase) containing its own dockerin, Trichoderma reesei CBHII (exoglucanase) fused with an exogenous dockerin from C. thermocellum, or Aspergillus aculeatus BGLI (β-glucosidase). The secreted dockerin-containing enzymes, CelA and CBHI, were randomly assembled to the surface-displayed mini CipA via cohesin-dockerin interactions. On the other hand, BGLI was independently assembled to the cell surface since we newly found that it already has a cell adhesion characteristic. We optimized the cellulosome activity and ethanol production by controlling the combination ratio among the four yeast strains. A mixture of cells with the optimized mini CipA:CelA:CBHII:BGLI ratio of 2:3:3:0.53 produced 1.80 g/l ethanol after 94 h, indicating about 20% increase compared with a consortium composed of an equal amount of each cell type (1.48 g/l).

Conclusions: We produced cellulosic ethanol using a cellulolytic yeast consortium, which is composed of cells displaying mini cellulosomes generated via random assembly of CelA and CBHII to a mini CipA, and cells displaying BGLI independently. One of the advantages of this system is that ethanol production can be easily optimized by simply changing the combination ratio of the different populations. In addition, there is no limitation on the number of enzymes to be incorporated into this cellulosome structure. Not only cellulases used in this study, but also any other enzymes, including cellulases and hemicellulases, could be applied just by fusing dockerin domains to the enzymes.

Show MeSH
Related in: MedlinePlus