Studying the rapid bioconversion of lignocellulosic sugars into ethanol using high cell density fermentations with cell recycle

Cory Sarks, Mingjie Jin, Trey K. Sato, Venkatesh Balan, Bruce E. Dale

Research output: Contribution to journalArticle

  • 23 Citations

Abstract

Background: The Rapid Bioconversion with Integrated recycle Technology (RaBIT) process reduces capital costs, processing times, and biocatalyst cost for biochemical conversion of cellulosic biomass to biofuels by reducing total bioprocessing time (enzymatic hydrolysis plus fermentation) to 48 h, increasing biofuel productivity (g/L/h) twofold, and recycling biocatalysts (enzymes and microbes) to the next cycle. To achieve these results, RaBIT utilizes 24-h high cell density fermentations along with cell recycling to solve the slow/incomplete xylose fermentation issue, which is critical for lignocellulosic biofuel fermentations. Previous studies utilizing similar fermentation conditions showed a decrease in xylose consumption when recycling cells into the next fermentation cycle. Eliminating this decrease is critical for RaBIT process effectiveness for high cycle counts. Results: Nine different engineered microbial strains (including Saccharomyces cerevisiae strains, Scheffersomyces (Pichia) stipitis strains, Zymomonas mobilis 8b, and Escherichia coli KO11) were tested under RaBIT platform fermentations to determine their suitability for this platform. Fermentation conditions were then optimized for S. cerevisiae GLBRCY128. Three different nutrient sources (corn steep liquor, yeast extract, and wheat germ) were evaluated to improve xylose consumption by recycled cells. Capacitance readings were used to accurately measure viable cell mass profiles over five cycles. Conclusion: The results showed that not all strains are capable of effectively performing the RaBIT process. Acceptable performance is largely correlated to the specific xylose consumption rate. Corn steep liquor was found to reduce the deleterious impacts of cell recycle and improve specific xylose consumption rates. The viable cell mass profiles indicated that reduction in specific xylose consumption rate, not a drop in viable cell mass, was the main cause for decreasing xylose consumption.

LanguageEnglish (US)
Article number73
JournalBiotechnology for Biofuels
Volume7
Issue number1
DOIs
StatePublished - May 15 2014

Profile

Bioconversion
Xylose
Sugars
Fermentation
fermentation
ethanol
sugar
Ethanol
Cell Count
Biofuels
Technology
biofuel
Yeast
Recycling
Biocatalysts
recycling
Zea mays
Saccharomyces cerevisiae
Enzymes
maize

Keywords

  • AFEX
  • Cell recycling
  • Ethanol fermentation
  • Lignocellulosic biofuel
  • RaBIT
  • Saccharomyces cerevisiae

ASJC Scopus subject areas

  • Energy(all)
  • Management, Monitoring, Policy and Law
  • Biotechnology
  • Renewable Energy, Sustainability and the Environment
  • Applied Microbiology and Biotechnology

Cite this

Studying the rapid bioconversion of lignocellulosic sugars into ethanol using high cell density fermentations with cell recycle. / Sarks, Cory; Jin, Mingjie; Sato, Trey K.; Balan, Venkatesh; Dale, Bruce E.

In: Biotechnology for Biofuels, Vol. 7, No. 1, 73, 15.05.2014.

Research output: Contribution to journalArticle

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abstract = "Background: The Rapid Bioconversion with Integrated recycle Technology (RaBIT) process reduces capital costs, processing times, and biocatalyst cost for biochemical conversion of cellulosic biomass to biofuels by reducing total bioprocessing time (enzymatic hydrolysis plus fermentation) to 48 h, increasing biofuel productivity (g/L/h) twofold, and recycling biocatalysts (enzymes and microbes) to the next cycle. To achieve these results, RaBIT utilizes 24-h high cell density fermentations along with cell recycling to solve the slow/incomplete xylose fermentation issue, which is critical for lignocellulosic biofuel fermentations. Previous studies utilizing similar fermentation conditions showed a decrease in xylose consumption when recycling cells into the next fermentation cycle. Eliminating this decrease is critical for RaBIT process effectiveness for high cycle counts. Results: Nine different engineered microbial strains (including Saccharomyces cerevisiae strains, Scheffersomyces (Pichia) stipitis strains, Zymomonas mobilis 8b, and Escherichia coli KO11) were tested under RaBIT platform fermentations to determine their suitability for this platform. Fermentation conditions were then optimized for S. cerevisiae GLBRCY128. Three different nutrient sources (corn steep liquor, yeast extract, and wheat germ) were evaluated to improve xylose consumption by recycled cells. Capacitance readings were used to accurately measure viable cell mass profiles over five cycles. Conclusion: The results showed that not all strains are capable of effectively performing the RaBIT process. Acceptable performance is largely correlated to the specific xylose consumption rate. Corn steep liquor was found to reduce the deleterious impacts of cell recycle and improve specific xylose consumption rates. The viable cell mass profiles indicated that reduction in specific xylose consumption rate, not a drop in viable cell mass, was the main cause for decreasing xylose consumption.",
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