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Enhanced xylose fermentation and ethanol production by engineered Saccharomyces cerevisiae strain.

Vilela Lde F, de Araujo VP, Paredes Rde S, Bon EP, Torres FA, Neves BC, Eleutherio EC - AMB Express (2015)

Bottom Line: We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation.However, the recombinant yeast fermented xylose slowly.The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

ABSTRACT
We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation. However, the recombinant yeast fermented xylose slowly. In this study, an evolutionary engineering strategy was applied to improve xylose fermentation by the xylA-expressing yeast strain, which involved sequential batch cultivation on xylose. The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity. It was also observed that when cells were grown in a medium containing higher glucose concentrations before being transferred to fermentation medium, higher rates of xylose consumption and ethanol production were obtained, demonstrating that xylose utilization was not regulated by catabolic repression. Results obtained by qPCR demonstrate that the efficiency in xylose fermentation showed by the evolved strain is associated, to the increase in the expression of genes HXT2 and TAL1, which code for a low-affinity hexose transporter and transaldolase, respectively. The ethanol productivity obtained after the introduction of only one genetic modification and the submission to a one-stage process of evolutionary engineering was equivalent to those of strains submitted to extensive metabolic and evolutionary engineering, providing solid basis for future applications of this strategy in industrial strains.

No MeSH data available.


Related in: MedlinePlus

Sugar consumption and ethanol production byS. cerevisiae. Cells of un-evolved (A) and evolved strains (B) were grown in YNB-medium supplemented with 4% glucose until mid-log phase, collected by centrifugation, washed with distilled water and transferred to fermentation medium containing 3% glucose and 1% xylose. The samples were collected in times of 0, 6, 20, 24, 28, 44, 48 hours and the supernatants were used to determine the concentration of glucose and xylose, in times of 24 and 48 hours the supernatants were used to determine the ethanol concentration. The results represent the mean ± standard deviation of at least three independent experiments.
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Fig1: Sugar consumption and ethanol production byS. cerevisiae. Cells of un-evolved (A) and evolved strains (B) were grown in YNB-medium supplemented with 4% glucose until mid-log phase, collected by centrifugation, washed with distilled water and transferred to fermentation medium containing 3% glucose and 1% xylose. The samples were collected in times of 0, 6, 20, 24, 28, 44, 48 hours and the supernatants were used to determine the concentration of glucose and xylose, in times of 24 and 48 hours the supernatants were used to determine the ethanol concentration. The results represent the mean ± standard deviation of at least three independent experiments.

Mentions: The evolutionary engineering strategy significantly improved the specific xylose consumption rate, and provided efficient ethanol production from this sugar cane-like xylose-glucose mixture. The ethanol yield and productivity showed by the evolved strain were 13% (0.51 × 0.45 g ethanol/g sugar) and 120% (0.42 × 0.19 g ethanol/g cell/h) higher, respectively, than that of the un-evolved strain (Figure 1A, B). The evolved strain did not show xylitol accumulation, unlike the un-evolved strain (results not shown).Figure 1


Enhanced xylose fermentation and ethanol production by engineered Saccharomyces cerevisiae strain.

Vilela Lde F, de Araujo VP, Paredes Rde S, Bon EP, Torres FA, Neves BC, Eleutherio EC - AMB Express (2015)

Sugar consumption and ethanol production byS. cerevisiae. Cells of un-evolved (A) and evolved strains (B) were grown in YNB-medium supplemented with 4% glucose until mid-log phase, collected by centrifugation, washed with distilled water and transferred to fermentation medium containing 3% glucose and 1% xylose. The samples were collected in times of 0, 6, 20, 24, 28, 44, 48 hours and the supernatants were used to determine the concentration of glucose and xylose, in times of 24 and 48 hours the supernatants were used to determine the ethanol concentration. The results represent the mean ± standard deviation of at least three independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385029&req=5

Fig1: Sugar consumption and ethanol production byS. cerevisiae. Cells of un-evolved (A) and evolved strains (B) were grown in YNB-medium supplemented with 4% glucose until mid-log phase, collected by centrifugation, washed with distilled water and transferred to fermentation medium containing 3% glucose and 1% xylose. The samples were collected in times of 0, 6, 20, 24, 28, 44, 48 hours and the supernatants were used to determine the concentration of glucose and xylose, in times of 24 and 48 hours the supernatants were used to determine the ethanol concentration. The results represent the mean ± standard deviation of at least three independent experiments.
Mentions: The evolutionary engineering strategy significantly improved the specific xylose consumption rate, and provided efficient ethanol production from this sugar cane-like xylose-glucose mixture. The ethanol yield and productivity showed by the evolved strain were 13% (0.51 × 0.45 g ethanol/g sugar) and 120% (0.42 × 0.19 g ethanol/g cell/h) higher, respectively, than that of the un-evolved strain (Figure 1A, B). The evolved strain did not show xylitol accumulation, unlike the un-evolved strain (results not shown).Figure 1

Bottom Line: We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation.However, the recombinant yeast fermented xylose slowly.The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil.

ABSTRACT
We have recently demonstrated that heterologous expression of a bacterial xylose isomerase gene (xylA) of Burkholderia cenocepacia enabled a laboratorial Saccharomyces cerevisiae strain to ferment xylose anaerobically, without xylitol accumulation. However, the recombinant yeast fermented xylose slowly. In this study, an evolutionary engineering strategy was applied to improve xylose fermentation by the xylA-expressing yeast strain, which involved sequential batch cultivation on xylose. The resulting yeast strain co-fermented glucose and xylose rapidly and almost simultaneously, exhibiting improved ethanol production and productivity. It was also observed that when cells were grown in a medium containing higher glucose concentrations before being transferred to fermentation medium, higher rates of xylose consumption and ethanol production were obtained, demonstrating that xylose utilization was not regulated by catabolic repression. Results obtained by qPCR demonstrate that the efficiency in xylose fermentation showed by the evolved strain is associated, to the increase in the expression of genes HXT2 and TAL1, which code for a low-affinity hexose transporter and transaldolase, respectively. The ethanol productivity obtained after the introduction of only one genetic modification and the submission to a one-stage process of evolutionary engineering was equivalent to those of strains submitted to extensive metabolic and evolutionary engineering, providing solid basis for future applications of this strategy in industrial strains.

No MeSH data available.


Related in: MedlinePlus