Autotrophic and electroautotrophic production of high-value compounds with engineered Cupriavidus necator strains

Intense research on C. necator based processes for single cell protein and biodegradable plastic (poly(3-hydroxybutyrate), PHB) production has been conducted since the 1970s. Recently, the facultative chemoautotroph bacterium is being discussed as promising biocatalyst in bioelectrochemical systems, which could intensify the transition from fossil to renewable energy sources by acting as energy storage system. Furthermore, the utilization of carbon dioxide as substrate has a decisive advantage over sugar-based biotechnological processes: There is no competition with the food industry. In this work, a cultivation medium was developed which meets the specific requirements for media utilized for bioelectrochemical processes. Furthermore, a new inducible plasmid system for C. necator was established successfully. Based on this work, the heterotrophic, autotrophic and electroautotrophic production of the terpene α-humulene was enabled and consequently examined at different scales. Starting from fructose, 2.4 g α humulene/L was produced; the highest α-humulene concentration reached so far in a biotechnological process. Up to 146 mg α-humulene/L was produced from inorganic substances (carbon dioxide and hydrogen). This concentration noticeably exceeds the maximum sesquiterpene concentrations reached during photoautotrophic processes so far. Finally, with a concentration of 11 mg α-humulene/L and a coulombic efficiency of maximum 0.2% the successful production in a bioelectrochemical system was demonstrated. In summary, new production routes for the important substance class of terpenes could be presented.