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

Abstract

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 degrees 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 degrees C and 85 degrees C experiments. The fermentation stoichiometry for T. neapolitana at 85 degrees 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.

Hydrogen production by the hyperthermophilic bacterium Thermotoga maritima part I: effects of sulfured nutriments, with thiosulfate as model, on hydrogen production and growth

“…Nevertheless, these yields (2–2.2 mol mol −1 ) were coherent with the range of H 2 molar yields (1.7–4.0 mol mol −1 ) reported in literature for T. maritima and T. neapolitana [16, 29, 39, 44, 53, 55, 68, 70–72]. It is the same for the highest QH 2 (5.6 mmol L −1 h −1 ) (Fig.…”

H2 synthesis from pentoses and biomass in Thermotoga spp.

“…The molar of yield of hydrogen on glucose was 3-4 in both species and similar to previously reported yields on glucose (Schröder et al 1994;van Ooteghem et al 2002van Ooteghem et al , 2004Eriksen et al 2008;Munro et al 2009;d'Ippolito et al 2010). This indicates that our cultures have been grown at conditions that are comparable to conditions generally used for hydrogen production studies in Thermotoga.…”

“…During the growth phase, the average volumetric hydrogen production rates were 2-3 times higher in T. neapolitana than in T. maritima cultures, and similar in magnitude to the hydrogen production rates of 0.8-0.9 mmol l -1 h -1 previously found in T. neapolitana under similar conditions (Munro et al 2009). Also the specific hydrogen production rates, estimated as the yield of hydrogen on biomass (Fig.…”

“…Individual cells were most productive in early stages of batch cultures but gradually their activity decreased. In some cultures, activity stopped before all sugar was taken up, a phenomenon that has been explained by decreasing pH (Eriksen et al 2008;Munro et al 2009) but also metabolites, CO 2 and hydrogen accumulated and may have repressed the cultures. We found no systematic differences in hydrogen production rates on pentoses compared to glucose.…”

“…Takahata et al (2001) found yields of 3.7 and 4 mol H 2 mol -1 glucose in T. petrophila and T. naphtophila, respectively, while van Niel et al (2002) found a yield of 3.8 mol H 2 mol -1 glucose in T. elfii. In T. neapolitana, which has been extensively characterised with respect to hydrogen production, van Ooteghem et al (2002van Ooteghem et al ( , 2004 reported H 2 yields at or even above 4 mol H 2 mol -1 glucose, Eriksen et al (2008) found 3.5-3.8 mol H 2 mol -1 glucose when no lactic acid was formed, Munro et al (2009) found 3.85 mol H 2 mol -1 glucose at the optimal temperature of 77°C, and d 'Ippolito et al (2010) found 4.05 mol H 2 mol -1 glucose, and that 12-15% of the hydrogen was produced from yeast extract added to the growth medium. Also in other hyperthermophilic bacteria, hydrogen yields on glucose may approach the theoretical maximum (Verhaart et al 2010).…”