Long-term Operation of Continuous Culture of the Hyperthermophilic archaeon,Thermococcus onnurineusfor Carbon Monoxide-dependent Hydrogen Production

Abstract

In this study, we performed a kinetic analysis of CO-dependent H(2)production by metabolically engineered Thermococcus onnurineus NA1, MC01 in terms of the cell activity as well as mass transfer rate. We conducted continuous cultures with varying dilution rate, CO flow rate, or agitation speed. Despite oscillations in cell density, the cultures reached steady states at all operating conditions. As the dilution rate increased from 0.1 to 0.3 h(-1), specific activity of H(2)production (SAHP) and volumetric cell production rate were linearly increased. Also, the SAHP remained almost constant at the fixed dilution rate of 0.3 h(-1)even though the CO transfer rate was changed by adjusting the CO flow rate or the agitation speed. This relationship could be expressed as a typical Luedeking-Piret model, implying that high cell density culture with a sufficient growth rate is essential to obtain higher H(2)productivity. On the other hand, more elevated CO transfer at the same dilution rate improved H(2)production rate (HPR) by the increase of the cell density, not in the rise of SAHP. Through the continuous culture, 108 mmol/g-cell/h and 121 mmol/L/h of SAHP and HPR, respectively, could be achieved at a dilution rate of 0.3 h(-1)with CO supply rate of 0.07 vvm and agitation speed of 700 rpm. Considering high H(2)production activity and long-term stability of the strain over 1,000 h, MC01 is confirmed to have an outstanding potential for CO-dependent H(2)production.