Acetate-assisted mixotrophy of hydrogen-oxidizing bacteria for enhanced microbial protein production in an electrolytic airlift reactor

Hydrogen-oxidizing bacteria (HOB) have emerged as promising microbial protein (MP) producers within the “power-to-protein” framework, yet autotrophic cultivation is constrained by low growth rates, limited CO₂ fixation, and suboptimal protein quality. Here, we evaluated HOB cultures in autotrophic, heterotrophic, and acetate-assisted mixotrophic modes. Results revealed that mixotrophy substantially enhanced performance: the CO₂ uptake rate increased by up to 211% compared to autotrophy, while biomass yields improved by 11–69%. Under optimized acetate supplementation (8–12 g/L), protein content reached 71.63% with a total amino acid level of 71.8 g/100 g cell dry weight (CDW), exceeding autotrophic cultivation. Microbial community analysis demonstrated that Xanthobacter dominated under moderate acetate conditions, maintaining CO₂ fixation and supporting high biomass accumulation. The system also achieved a maximum current density of 350 A/m², indicating efficient electron utilization. Collectively, this study demonstrates that acetate-assisted mixotrophy in an electrolytic airlift reactor is an effective strategy for cost-efficient microbial protein production, offering new perspectives for electricity-driven biomanufacturing and sustainable carbon capture.