Development of THERMOphilic microorganisms for SYNgas CONversion to biobased fuels and chemicals

The decreasing availability of fossil fuels and the consequences of climate change increase the demand for biofuels and bioproducts from renewable resources and waste within a circular economy. Syngas, which contains various ratios of CO₂, CO, and H₂, is generated as waste gas in industrial processes. Acetogenic bacteria convert syngas into value-added carbon-based chemicals. Given the high temperatures of these industrial gas streams, syngas conversions (fermentations) at temperatures between 50–80°C are attractive. Within the BMBF-funded consortium ThermoSynCon, four partners from different German universities bundled their expertise in a research consortium to establish a syngas fermentation production platform using new thermophilic isolates or engineered strains.

Within the project, we enriched and isolated new thermophilic acetogenic bacteria and created a strain collection of thermophilic acetogens. Small-scale growth studies and fermentation studies of the new isolates on H₂+CO₂, CO, and syngas were performed, and the isolates were characterized and compared in their performance to the few known thermophilic acetogens, including the promising species T. kivui (T_OPT 66°C) and M. thermoacetica. We improved the bioenergetics models for T. kivui and M. thermoacetica based on detailed omics, biochemical, physiological, and genetic studies. We developed bioreactor technologies for (syn)gas fermentation at elevated temperatures (50–80°C), optimized the process control, and evaluated the performance of T. kivui, and M. thermoacetica in bioreactors. Genetic tools for T. kivui were improved, with the goal of gaining a fundamental understanding of its physiology and constructing superior strains to produce alcohols from syngas. We subsequently genetically engineered T. kivui for ethanol production and tested the strains in the bioreactor, achieving a 50-mM titer in a continuous bioreactor.

Overall, the project provided deep insights into the metabolism of thermophilic acetogens, and proof-of-concept results of syngas conversion to ethanol in a continuous bioreactor. The road is paved towards a thermophilic syngas fermentation platform!