Genetische Manipulation und Stammoptimierung von Clostridium ljungdahlii zur Produktion von Biobutanol mittels Synthesegasfermentation
Stoffwechselphysiologie, Biochemie und Genetik der Mikroorganismen
Zusammenfassung der Projektergebnisse
The fermentation of synthesis gas (a mix of mainly carbon monoxide, hydrogen, and carbon dioxide) with acetogenic bacteria is an attractive biotechnological route to mitigate carbon pollution and produce fuels and chemicals to offset fossil sources. This technology has now reached the step of being transferred to a commercial scale. However, many aspects of acetogenic metabolism are not very well understood. Both metabolic engineering strategies as well as bioprocess optimization have to be considered to further improve the overall efficacy of this promising biotechnology. This research proposal aimed at testing genetically modified Clostridium ljungdahlii in a twostage continuous bioreactor setup for the production of n-butanol from n-butyrate and syngas. With this, the long-term stability of the genetically modified strains, under application-relevant conditions, was aimed to be studied. At the same time, the bioprocessing for the two-stage bioreactor with in-line product extraction was aimed to be optimized. Unfortunately, the genetically modified strains were not yet available when the research commenced. Therefore, an alternative strategy was conducted to produce chemicals from syngas with combined bioprocesses involving different wild-type bacteria. With this, no genetic modifications were necessary to produce proposed products. The choice of in-line product extraction methods was an important consideration for the design of the overall bioprocessing scheme. Different strategies were tested and the advantages and disadvantages were compared and discussed. The overall process scheme starts with the production of acetate and ethanol via syngas fermentation with wild-type C. ljungdahlii. In a second step, acetate and ethanol are chain-elongated via the reverse β-oxidation pathway to medium chain carboxylic acids, such as n-butyrate, n-caproate, and n-caprylate, with wild-type Clostridium kluyveri. The last step involves, again, C. ljungdahlii to reduce the medium chain carboxylic acids to the respective alcohols (i.e., n-butanol, n-hexanol, n-octanol) with reducing power from syngas. Aspects of all three steps were studied separately during the funding period. Furthermore, a process could be established in which all three steps commenced simultaneously in one bioreactor with a defined co-culture. However, incompatibilities of bioprocessing parameters and competition of the single bioprocesses let us to conclude that an optimization of the separate bioprocesses will most likely be the strategy of choice toward an industrially relevant bioprocessing scheme.
Projektbezogene Publikationen (Auswahl)
- (2016). A narrow pH range supports butanol, hexanol, and octanol production from syngas in a continuous coculture of Clostridium ljungdahlii and Clostridium kluyveri with in-line product extraction. Frontiers in Microbiology, 7: No. 1773
Richter H, Molitor B, Diender M, Sousa DZ, Angenent LT
(Siehe online unter https://doi.org/10.3389/fmicb.2016.01773) - (2016). Carbon recovery by fermentation of CO-rich off gases – turning steel mills into biorefineries. Bioresource Technology, 215: 386-396
Molitor B, Richter H, Martin ME, Jensen RO, Juminaga A, Mihalcea C, Angenent LT
(Siehe online unter https://doi.org/10.1016/j.biortech.2016.03.094) - (2016). Ethanol production in syngas-fermenting Clostridium ljungdahlii is controlled by thermodynamics rather than by enzyme expression. Energy and Environmental Science, 9: 2392-2399
Richter H, Molitor B, Wei H, Chen W, Aristilde L, Angenent LT
(Siehe online unter https://doi.org/10.1039/c6ee01108j) - (2017). Upgrading syngas fermentation effluent using Clostridium kluyveri in a continuous fermentation. Biotechnology for Biofuels, 10: No. 83
Gildemyn S, Molitor B, Usack J, Nguyen M, Rabaey K, Angenent LT
(Siehe online unter https://doi.org/10.1186/s13068-017-0764-6)
