Oxygen in the mix: is oxic microbial electrosynthesis a potential alternative for biomass production?

Oxic microbial electrosynthesis (oMES) allows the utilization of renewable electricity and industrial gas streams containing CO2 and O2 for biomass production by cultivating aerobic, autotrophic, hydrogen-oxidizing bacteria, commonly known as Knallgas bacteria. oMES is likely not a direct competitor to conventional anoxic microbial electrosynthesis as harnessing aerobic hydrogen-oxidizing bacteria depends on energetically inefficient assimilatory CO2 reduction pathways. However, it might be a complementary approach to classical biomass production from the perspective of limited land use and the availability of cheap renewable energy. The best characterized Knallgas bacterium is Cupriavidus necator. Extensively studied as lithoautotrophic production host, C. necator already offers a broad arsenal of genetic tools. In contrast, mechanistical knowledge about the recently discovered Kyrpidia spormannii is limited, but this species shows remarkable growth when cultivated as cathodic biofilm in bioelectrochemical systems. In addition, first experiments indicate a low energy demand for biomass production, which is in the order of magnitude of gas fermentation with C. necator or heterotrophic and methanotrophic technologies. Still, many aspects of the electrochemical cultivation of K. spormannii need to be better understood and rigorously improved to be a competitive technology in the making, including electron transfer and microbial kinetics, cultivation conditions, mass and energy balances, and reactor design.