Journal
METABOLIC ENGINEERING
Volume 53, Issue -, Pages 14-23Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.ymben.2019.01.003
Keywords
Acetogens; Wood-Ljungdahl pathway; Polyhydroxyalkanoate; Gas fermentation; C. autoethanogenum; PHB
Categories
Funding
- Australian Research Council [ARC LP140100213]
- Lanzatech
- Queensland node of Metabolomics Australia, a National Collaborative Research Infrastructure Strategy (NCRIS)
- European Union's Horizon 2020 research and innovation programme [668997]
- NNF Center for Biosustainability [Quantitative Modeling of Cell Metab] Funding Source: researchfish
- Novo Nordisk Fonden [NNF10CC1016517] Funding Source: researchfish
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Gas fermentation is emerging as an economically attractive option for the sustainable production of fuels and chemicals from gaseous waste feedstocks. Clostridium autoethanogenum can use CO and/or CO2 + H-2 as its sole carbon and energy sources. Fermentation of C. autoethanogenum is currently being deployed on a commercial scale for ethanol production. Expanding the product spectrum of acetogens will enhance the economics of gas fermentation. To achieve efficient heterologous product synthesis, limitations in redox and energy metabolism must be overcome. Here, we engineered and characterised at a systems-level, a recombinant poly-3-hydroxybutyrate (PHB)-producing strain of C. autoethanogenum. Cells were grown in CO-limited steady-state chemostats on two gas mixtures, one resembling syngas (20% H-2) and the other steel mill off-gas (2% H-2). Results were characterised using metabolomics and transcriptomics, and then integrated using a genome-scale metabolic model reconstruction. PHB-producing cells had an increased expression of the Rnf complex, suggesting energy limitations for heterologous production. Subsequent optimisation of the bioprocess led to a 12-fold increase in the cellular PHB content. The data suggest that the cellular redox state, rather than the acetyl-CoA pool, was limiting PHB production. Integration of the data into the genome-scale metabolic model showed that ATP availability limits PHB production. Altogether, the data presented here advances the fundamental understanding of heterologous product synthesis in gas-fermenting acetogens.
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