430756 Quantifying the Effects of Oxygen Utilization Rate on Ethanol Production By S. Stipitis Under Controlled Chemostat

Thursday, November 12, 2015: 12:55 PM
258 (Salt Palace Convention Center)
Min Hea Kim, Chemical Engineering, Auburn University, Auburn, AL, Q. Peter He, Chemical Engineering, Tuskegee University, Tuskegee, AL and Jin Wang, Auburn University, Auburn, AL

Quantifying the effects of oxygen utilization rate on ethanol production by S. stipitis under controlled chemostat

Min Hea Kim1, Q. Peter He2 and Jin Wang1

(1)Department of Chemical Engineering, Auburn University, Auburn, AL 36849, USA

(2)Department of Chemical Engineering, Tuskegee University, Tuskegee, AL 36088, USA


Lignocellulosic materials offer a potential source of carbon substrates (glucose and xylose) for the production of ethanol by fermentation. Scheffersomyces stipitis is a native yeast strain best capable of utilizing xylose to ethanol. Since S. stipitis is a respiratory yeast strain, the xylose fermentation performance depends significantly on the oxygenation level of the culture. High aeration rate results in fast cell growth and acetic acid production, while very low aeration (oxygen-limited) often results in xylitol production, both at the expense of reduced ethanol production. Only optimized microaerobic condition promotes ethanol production by maintaining cell viability and NADH balance. Hence, it is critical to determine the optimal oxygen utilization rate (OUR) for ethanol production by S. stipitis. In order to quantitatively study the effect of OUR on the fermentation performance, accurate control of OUR is essential. Several studies have been reported on the optimum oxygenation conditions for ethanol fermentation by S. stipitis [1-4]. Among these studies, most of the experiments were carried out using batch cultures grown in flasks where the Oxygen Transfer Rate (OTR) and/or Dissolved Oxygen (DO) were not effectively controlled. Different OTR levels have been tested simply by changing volume of media, airflow rate, and agitation speed. However, our research shows that the inaccurate control of OTR/OUR is problematic in these studies. In addition, our research indicates that the optimum OUR alone (i.e., without information on carbon utilization) does not correlate well with ethanol yield. Our research shows that with the same OUR condition tested under controlled chemostat, the ethanol yield changes due to the change of metabolic status or phenotypes of S. stipitis. Different phenotypes exist under a single OUR condition, which was verified by Principal Component Analysis (PCA) which enables the extraction of correlations between different cellular physiology with respect to  carbon uptake and OUR. This helps us understand and quantify the metabolic mechanism of OUR in continuous fermentation. References

  1. Su Y, Willis LB, Jeffries TW (2015), Effects of aeration on growth, ethanol and polyol accumulation by Spathaspora passalidarum NRRL Y-27907 and Scheffersomyces stipitis NRRL Y-7124. Biotechnol  Bioeng, 112, 457-469
  2. Slininger PJ, Dien BS, Lomont JM, Bothast RJ, Ladisch MR (2014), Evaluation of a kinetic model for computer simulation of growth and fermentation by Scheffersomyces (Pichia ) stipitis Fed D-xylose. Biotechnol Bioeng, 111, 1532-1540
  3. Silva JPA, Mussatto SI, Roberto IC, Teixeira JA (2012), Fermentation medium and oxygen transfer conditions that maximize the xylose conversion to ethanol by Pichia stipitis. Renewable Energy, 37, 259-265
  4. Unrean P, Nguyen NHA (2012), Metabolic pathway analysis of Scheffersomyces (Pichia) stipitis: effect of oxygen availability on ethanol synthesis and flux distributions. Appl Microbiol Biotechnol, 94, 1387-1398

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