Cost-Efficient Autotrophic High-Cell-Density Cultivation of Cupriavidus necator Enabled by Model-Based Gas Supply

Cultivating hydrogen-oxidizing bacteria (HOB), such as Cupriavidus necator, using $H_2$ , ${\text{CO}}_2$ , and $O_2$ offers a promising route for ${\text{CO}}_2$ valorization into chemicals and materials. To enhance cultivation efficiency in a lab-scale gas fermenter lacking a gas recycling system, an automated gas supply strategy based on real-time ${\text{CO}}_2$ and $O_2$ monitoring was developed. Fine-tuning gas delivery is essential to ensure an adequate supply for cellular growth while minimizing excess gas, particularly $H_2$ , that leaves the bioreactor unused, to improve process economics. In the absence of ATEX-compliant $H_2$ sensors, a soft sensor was implemented to estimate dissolved $H_2$ concentrations from $O_2$ uptake rates and growth phase identification. Total gas flow was controlled according to the $O_2$ requirements of the cells. This strategy reduced overall gas and $H_2$ consumption by 67%. In addition, a high-cell-density medium was formulated by integrating published recipes with Inductively Coupled Plasma Optical Emission Spectroscopy and nutrient inhibition testing. The optimized medium increased biomass yield from 15 g/L to 53 g/L, with 75% of the dry weight consisting of the bioplastic poly(3-hydroxybutyrate), without requiring nutrient addition or pH control. Together, these strategies improve the scalability, efficiency, and sustainability of ${\text{CO}}_2$ -based cultivation of hydrogen-oxidizing bacteria.