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.