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Prolonged conversion of n-butyrate to n-butanol with Clostridium saccharoperbutylacetonicum in a two-stage continuous culture with in-situ product removal†
Article first published online: 7 DEC 2011
Copyright © 2011 Wiley Periodicals, Inc.
Biotechnology and Bioengineering
Volume 109, Issue 4, pages 913–921, April 2012
How to Cite
Richter, H., Qureshi, N., Heger, S., Dien, B., Cotta, M. A. and Angenent, L. T. (2012), Prolonged conversion of n-butyrate to n-butanol with Clostridium saccharoperbutylacetonicum in a two-stage continuous culture with in-situ product removal. Biotechnol. Bioeng., 109: 913–921. doi: 10.1002/bit.24380
- Issue published online: 21 FEB 2012
- Article first published online: 7 DEC 2011
- Accepted manuscript online: 17 NOV 2011 08:00AM EST
- Manuscript Accepted: 10 NOV 2011
- Manuscript Revised: 11 OCT 2011
- Manuscript Received: 11 JUL 2011
- National Institutes of Food and Agriculture (NIFA). Grant Number: 2007-35504-05381
- ABE fermentation;
- carboxylate conversion;
- solventogenic Clostridium species;
- pH auxostat;
- gas stripping
n-Butanol was produced continuously in a two-stage fermentor system with integrated product removal from a co-feed of n-butyric acid and glucose. Glucose was always required as a source of ATP and electrons for the conversion of n-butyrate to n-butanol and for biomass growth; for the latter it also served as a carbon source. The first stage generated metabolically active planktonic cells of Clostridium saccharoperbutylacetonicum strain N1-4 that were continuously fed into the second (production) stage; the volumetric ratio of the two fermentors was 1:10. n-Butanol was removed continuously from the second stage via gas stripping. Implementing a two-stage process was observed to dramatically dampen metabolic oscillations (i.e., periodical changes of solventogenic activity). Culture degeneration (i.e., an irreversible loss of solventogenic activity) was avoided by periodical heat shocking and re-inoculating stage 1 and by maintaining the concentration of undissociated n-butyric acid in stage 2 at 3.4 mM with a pH-auxostat. The system was successfully operated for 42 days during which 93% of the fed n-butyrate was converted to n-butanol at a production rate of 0.39 g/(L × h). The molar yields Yn-butanol/n-butyrate and Yn-butanol/glucose were 2.0, and 0.718, respectively. For the same run, the molar ratio of n-butyrate to glucose consumed was 0.358. The molar yield of carbon in n-butanol produced from carbon in n-butyrate and glucose consumed (Yn-butanol/carbon) was 0.386. These data illustrate that conversion of n-butyrate into n-butanol by solventogenic Clostridium species is feasible and that this can be performed in a continuous system operating for longer than a month. However, our data also demonstrate that a relatively large amount of glucose is required to supply electrons and ATP for this conversion and for cell growth in a continuous culture. Biotechnol. Bioeng. 2012; 109:913–921. © 2011 Wiley Periodicals, Inc.