Abstract
Acetic acid is an important chemical raw material that can be produced directly from sugars in lignocellulosic biomass. Development of kinetic models that capture the bioconversion dynamics of multiple sugar systems will be critical to optimization and process control in future lignocellulosic biorefinery processes. In this work, a kinetic model was developed for the single- and dual-substrate conversion of xylose and glucose to acetic acid using the acetogen Moorella thermoacetica. Batch fermentations were performed experimentally at 20 g L−1 total sugar concentration using synthetic glucose, xylose, and a mixture of glucose and xylose at a 1:1 ratio. The product yield, calculated as total product formed divided by total sugars consumed, was 79.2, 69.9, and 69.7 % for conversion of glucose, xylose, and a mixture of glucose and xylose (1:1 ratio), respectively. During dual-substrate fermentation, M. thermoacetica demonstrated diauxic growth where xylose (the preferred substrate) was almost entirely consumed before consumption of glucose began. Kinetic parameters were similar for the single-substrate fermentations, and a strong linear correlation was determined between the maximum specific growth rate μ max and substrate inhibition constant, K s . Parameters estimated for the dual-substrate system demonstrated changes in the specific growth rate of both xylose and glucose consumption. In particular, the maximum growth rate related to glucose tripled compared to the single-substrate system. Kinetic growth is affected when multiple substrates are present in a fermentation system, and models should be developed to reflect these features.
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Abbreviations
- S :
-
Substrate concentration (g L−1)
- X :
-
Cell mass concentration (g L−1)
- P :
-
Product concentration (g L−1)
- r x :
-
Reaction rate of cell growth (g L−1 h−1)
- r s :
-
Reaction rate of substrate consumption (g L−1 h−1)
- r p :
-
Reaction rate of product formation (g L−1 h−1)
- μ g,i :
-
Specific growth rate (h−1)
- μ max,gi :
-
Maximum specific growth rate (h−1)
- K s :
-
Substrate saturation constant (g L−1)
- K 1 :
-
Substrate inhibition constant
- P max :
-
Maximum product concentration before inhibition (g L−1)
- K d :
-
Cell death rate constant (h−1)
- Y xs :
-
Cell growth yield from substrate (\({\text{g cells g}}^{ - 1} {\text{substrate}}\))
- Y px :
-
Product yield from cells (\({\text{g product g}}^{ - 1} {\text{cells}}\))
- Y ps :
-
Product yield from substrate, or effective product yield (\({\text{g product g}}^{ - 1} {\text{substrate}}\))
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Acknowledgments
This project is supported by Agriculture and Food Research Initiative Competitive Grant No. 2011-68005-30407 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture. The University of Washington Denman Professorship Fund provided financial support.
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Schmitt, E., Bura, R., Gustafson, R. et al. Kinetic modeling of Moorella thermoacetica growth on single and dual-substrate systems. Bioprocess Biosyst Eng 39, 1567–1575 (2016). https://doi.org/10.1007/s00449-016-1631-8
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DOI: https://doi.org/10.1007/s00449-016-1631-8