Bio-Hydrogen Production By Continuous Culture of Hyperthermophilic Archaeon from Carbon Monoxide

The hyperthermophilic archaeon, Thermococcus onnurineus NA1 was known for a good bio-hydrogen producer through the water-gas shift (WGS) reaction (CO + H₂O → CO₂ + H₂). Recently, we reported that H₂ productivity from carbon monoxide (CO) of the metabolically engineered T. onnurineusNA1, MC01, was enhanced significantly (at least 2-fold increase), compared to that of wild-type strain.

In this study, we assessed kinetic parameters for cell growth and bio-H₂ production from CO by conducting the continuous cultivation of MC01 with varying dilution rate, CO supply rate, or agitation speed. Practically, the CSTR fermentation of MC01 using CO as a sole carbon could be performed over a month without any technical problem, implicating that the process is feasible to produce hydrogen continuously for a long-term basis. Based on the results, both cell growth and H₂ productivity were linearly correlated with dilution rate unless CO was not limited. At a fixed dilution rate of 0.3 h^-1, H₂ production rate was linearly increased depending on CO supply rate up to 240 ml/min, which is corresponded to 0.12 vvm. However, at CO rate of 300 ml/min, both cell growth and H₂ production rate considerably decreased, indicating CO inhibition toward cell growth and H₂ production. Additionally, the increase in agitation speed was also effective in enhancing H₂ production. It is considered that enhancing mass transfer by increasing CO supply or high agitation speed seemed likely a critical determinant for cell growth and H₂ production rate from CO.