Exploration of formate as a liquid organic hydrogen carrier in biohydrogen production through evolutionary and process engineering of hyperthermophilic archaeon.

Hydrogen (H2) is considered a promising renewable energy source, but its storage and delivery present significant challenges. Liquid organic hydrogen carriers (LOHC) offer a potential solution to this problem, with formate as a top candidate for LOHC. This study focused on developing technology for biological H2 production from formate by utilizing the hyperthermophilic archaeon Thermococcus onnurineus NA1. An engineered strain, WTF-350 T, was developed through adaptive evolution using formate and exhibited 3.6-4.0 times enhanced cell growth, formate consumption, and H2 production compared to the wild-type strain. Optimizing fermentation processes through pH-stat, fed-batch mode, and pyruvate supplementation led to a 2.0-2.5 times increase in cell density and H2 production rate. Moreover, formic acid, produced by the electroreduction of carbon dioxide (CO2), was found to be an effective feedstock for biohydrogen production. This study successfully demonstrated the potential of integrating CO2 electroreduction and biohydrogen production for a sustainable hydrogen economy.