Continuous hydrogen production by the hyperthermophilic archaeon, Thermococcus kodakaraensis KOD1

The hydrogen (H₂) production potential of the hyperthermophilic archaeon, Thermococcus kodakaraensis KOD1 was evaluated at 85°C. In batch cultivation using a complex medium supplemented with elemental sulfur (S ⁰), evolution of H₂S and CO₂ was observed in the gas phase. When S⁰ was omitted and pyruvate or starch was added in the medium, the cells produced H₂ at high levels instead of H ₂S. As the level of H₂ appeared to correlate with the specific growth rate, analysis in continuous cultures was performed to develop a continuous H₂ production system. In a steady-state condition at a dilution rate of 0.2 h^-1, a continuous H₂ production rate (per gram dry weight, gdw) of 24.9 and 14.0 mmol gdw^-1 h^-1 was observed in media supplemented with pyruvate and starch, respectively. In both cultivations, a high accumulation of acetate and alanine was found as metabolites. When the dilution rates were elevated in the medium with pyruvate, steady-state growth was observed up to 0.8 h^-1, and a maximum H ₂ production rate of 59.6 mmol gdw^-1 h^-1 was obtained. Based on the experimental results along with data of the entire genome sequence, the metabolic pathway of the strain relating to starch and pyruvate degradation is discussed.