Hydrogen production from C1 compounds by a novel marine hyperthermophilic archaeon Thermococcus onnurineus NA1

Abstract

A novel marine hyperthermophile, Thermococcus onnurineus NA1, was found to grow on C1 carbon compounds, such as formate and carbon monoxide (CO), and produce hydrogen (H2). In the present study, the growth and H2 production of NA1 were examined to determine its potential as H2 producer. NA1 showed relatively high specific growth rates, 0.48 h−1 and 0.40 h−1 with CO (20%, v/v) and formate (100 mM), respectively, when cultivated in batch mode in a minimal salt medium fortified with 1.0 g L−1 yeast extract. On the other hand, cell growth in both cases stopped at approximately 6 h and the final cell densities were extremely low at 18.2 and 12.1 mg protein L−1 with CO and formate, respectively. The maximum final cell density could be improved greatly to 36.0 mg protein L−1 by optimizing CO content (50%, v/v) and yeast extract concentration (4.0 g L−1), but it was still very low. During the cell growth, formate and CO were used as energy source rather than carbon source. In the resting cell experiments, NA1 exhibited remarkably high H2 production activities as 385.0 and 207.5 μmol mg protein−1 h−1 for CO and formate, respectively. When formate (100 mM) or CO (100%, v/v) was added repeatedly at 30–35 h intervals, NA1 showed consistent H2 production for 3 cycles with a yield of approximately 1.0 mol H2 mol−1 for both CO and formate. This study suggests that T. onnurineus NA1 has a high H2 production potential from formate or CO but a method for achieving a high cell density culture is needed.