The fermentation stoichiometry of Thermotoga neapolitana and influence of temperature, oxygen, and pH on hydrogen production

The hyperthermophilic bacterium, Thermotoga neapolitana , has potential for use in biological hydrogen (H 2 ) production. The objectives of this study were to (1) determine the fermentation stoichiometry of Thermotoga neapolitana and examine H 2 production at various growth temperatures, (2) investigate the effect of oxygen (O 2 ) on H 2 production, and (3) determine the cause of glucose consumption inhibition. Batch fermentation experiments were conducted at temperatures of 60, 65, 70, 77, and 85°C to determine product yield coefficients and volumetric productivity rates. Yield coefficients did not show significant changes with respect to growth temperature and the rate of H 2 production reached maximum levels in both the 77°C and 85°C experiments. The fermentation stoichiometry for T. neapolitana at 85°C was 3.8 mol H 2 , 2 mol CO 2 , 1.8 mol acetate, and 0.1 mol lactate produced per mol of glucose consumed. Under microaerobic conditions H 2 production did not increase when compared to anaerobic conditions, which supports other evidence in the literature that T. neapolitana does not produce H 2 through microaerobic metabolism. Glucose consumption was inhibited by a decrease in pH. When pH was adjusted with buffer addition cultures completely consumed available glucose. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009