CaproSyn - CO₂-based production of caproic acid by engineered Acetobacterium woodii and Clostridium drakei, applying a synthetic co-culture 

 

CaproSyn also combined the expertise of two academic groups, from microbiology and molecular biology (Dr. F.R. Bengelsdorf, UULM) and bioprocess engineering (Prof. Dr. D. Weuster-Botz, TUM). The goal of CaproSyn was to develop an optimized synthetic co-culture that produces caproate from CO₂, CO, and H₂ via lactate. The anaerobic co-culture consisted of Clostridium drakei FP and different genetically modified A. woodii strains, which are able to produce lactate(Baur et al., submitted). In some these strains, a the pyruvate formate lyase from Clostridium pasteurianum was overexpressed in addition to the D-lactate dehydrogenase from Leuconostoc mesenteroides (Baur et al., submitted). Although A. woodii is sensitive to carbon monoxide (CO), carefully dosed CO concentrations were found to enhance growth and lactate production of respective strains (Stock et al., 2026). In the synthetic co-culture, C. drakei FP consumed the lactate produced by recombinant A. woodii cells and produced butyrate and caproate. In A. woodii, formate is the first intermediate in the Wood-Ljungdahl pathway and can be forced to excreted by elevated H₂ partial pressures in bioreactors. Overexpression of the pyruvate formate lyase provided a branch for the carbon flux of the Wood-Ljungdahl pathway to lactate via formate and pyruvate. Fluorescence in situ hybridization (FISH), combined with flow cytometry and qPCR were used to quantify the growth of both strains in co-culture. qPCR proved to be more sensitive, reliable, faster, and more resource-efficient than FISH combined with flow cytometry. In summary, the overarching goal of CaproSyn was to maximize the carbon flux from CO₂ to butyrate and caproate through the application of metabolic engineering and reaction engineering, which was realized through the described interdisciplinary research approach. 
 

 

Baur, K. S., Rühle, B., Reith, T., Krieg, A., Bengelsdorf, F.R. (2025). Protocol to obtain genetically engineered Acetobacterium woodii and Eubacterium callanderi strains. STAR Protocols, 6, 104011, https://doi.org/10.1016/j.xpro.2025.104011

Stock, A., Sotzeck, I., Baur, K. S., Bengelsdorf, F. R., Weuster-Botz, D. (2026). Careful CO addition enhances autotrophic D-lactate formation with engineered Acetobacterium woodii. Engineering in Life Sciences 26, e70072. doi.org/10.1002/elsc.70072

Baur, K. S., Stock, A., Weuster-Botz, D., Bengelsdorf, F., R. (2026). Improving autotrophic D-lactate production by heterologous expression of a pyruvate formate lyase in Acetobacterium woodii. Applied Microbiology and Biotechnology, eingereicht.

Baur, K. S., Wagenblast, F. M., Picco, G. A., Poehlein, A., Daniel, R., Bengelsdorf, F. R. (2026). Physiological and genomic characterization of Clostridium drakei FP as a stable partner for synthetic co-culture. Biotechnology for Biofuels and Bioproducts, eingereicht.