Abstract
Clostridium ljungdahlii (C. ljungdahlii, CLJU) is natively endowed producing acetic acid, 2,3-butandiol, and ethanol consuming gas mixtures of CO2, CO, and H2 (syngas). Here, we present the syngas-based isobutanol formation using C. ljungdahlii harboring the recombinant amplification of the “Ehrlich” pathway that converts intracellular KIV to isobutanol. Autotrophic isobutanol production was studied analyzing two different strains in 3-L gassed and stirred bioreactors. Physiological characterization was thoroughly applied together with metabolic profiling and flux balance analysis. Thereof, KIV and pyruvate supply were identified as key “bottlenecking” precursors limiting preliminary isobutanol formation in CLJU[KAIA] to 0.02 g L–1. Additional blocking of valine synthesis in CLJU[KAIA]:ilvE increased isobutanol production by factor 6.5 finally reaching 0.13 g L–1. Future metabolic engineering should focus on debottlenecking NADPH availability, whereas NADH supply is already equilibrated in the current generation of strains.
Highlights
Isobutanol is an important commodity in the chemical, food, and pharmaceutical industries with rising global market size (Karabektas and Hosoz, 2009; Grand View Research, 2016)
Before investigating a recombinant isobutanol formation based on syngas, a reference process (REF) was used to analyze growth, product formation, and substrate uptake of the C. ljungdahlii wildtype strain (CLJU[WT]) (Figure 2)
A syngasbased batch cultivation in a steadily gassed 3-L bioreactor was performed in duplicates
Summary
Isobutanol is an important commodity in the chemical, food, and pharmaceutical industries with rising global market size (Karabektas and Hosoz, 2009; Grand View Research, 2016). It is a promising fuel substitute showing lower vapor pressure, volatility, and hygroscopicity and higher energy density than bioethanol (Atsumi et al, 2010). The production of isobutanol is mainly based on petroleum resources. Synthesis gas (syngas) represents a further promising substrate for biotechnological production of isobutanol as it can replace fossilbased resources and simultaneously prevent a competition with the availability of food. Syngas is a mixture mainly composed of carbon monoxide (CO), carbon dioxide (CO2), and hydrogen (H2) derived from agricultural, industrial, and municipal wastes and representing an inexpensive
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