Department of Microbiology, Cornell University, Ithaca, New York 14853.
Appl Environ Microbiol. 1988 Jun;54(6):1457-61. doi: 10.1128/aem.54.6.1457-1461.1988.
Hydrogen partial pressures were measured in a thermophilic coculture comprised of a eubacterial rod which oxidized acetate to H(2) and CO(2) and a hydrogenotrophic methanogen, Methanobacterium sp. strain THF. Zinder and Koch (S. H. Zinder and M. Koch, Arch. Microbiol. 138:263-272, 1984) originally predicted, on the basis of calculations of Gibbs free energies of reactions, that the H(2) partial pressure near the midpoint of growth of the coculture should be near 4 Pa (ca. 4 x 10 atm; ca. 0.024 muM dissolved H(2)) for both organisms to be able to conserve energy for growth. H(2) partial pressures in the coculture were measured to be between 20 and 50 Pa (0.12 to 0.30 muM) during acetate utilization, approximately one order of magnitude higher than originally predicted. However, when DeltaG(f) (free energy of formation) values were corrected for 60 degrees C by using the relationship DeltaG(f) = DeltaH(f) - TDeltaS (DeltaH(f) is the enthalpy or heat of formation, DeltaS is the entropy value, and T is the temperature in kelvins), the predicted value was near 15 Pa, in closer agreement with the experimentally determined values. The coculture also oxidized ethanol to acetate, a more thermodynamically favorable reaction than oxidation of acetate to CO(2). During ethanol oxidation, the H(2) partial pressure reached values as high as 200 Pa. Acetate was not used until after the ethanol was consumed and the H(2) partial pressure decreased to 40 to 50 Pa. After acetate utilization, H(2) partial pressures fell to approximately 10 Pa and remained there, indicating a threshold for H(2) utilization by the methanogen. Axenic cultures of the acetate-oxidizing organism were combined with pure cultures of either Methanobacterium sp. strain THF or Methanobacterium thermoautotrophicum DeltaH to form reconstituted acetate-oxidizing cocultures. The H(2) partial pressures measured in both of these reconstituted cocultures were similar to those measured in the original acetate-oxidizing rod coculture. Since M. thermoautotrophicum DeltaH did not use formate as a substrate, formate is not necessarily involved in interspecies electron transfer in this coculture.
在一个嗜热共培养物中测量了氢气分压，该共培养物由一种将乙酸氧化为 H(2) 和 CO(2) 的真细菌棒和一种产氢甲烷菌 Methanobacterium sp. strain THF 组成。Zinder 和 Koch（S. H. Zinder 和 M. Koch，Arch. Microbiol. 138:263-272, 1984）最初根据反应吉布斯自由能的计算预测，对于两种能够为生长保存能量的生物体，共培养物中生长中点附近的 H(2)分压应该接近 4 Pa（约 4 x 10 大气压；约 0.024 μM 溶解 H(2)）。在乙酸利用过程中，共培养物中的 H(2)分压测量值在 20 至 50 Pa（0.12 至 0.30 μM）之间，比最初预测的高约一个数量级。然而，当使用 DeltaG(f)（形成自由能）值与 60°C 时的关系 DeltaG(f) = DeltaH(f) - TDeltaS（DeltaH(f)是形成焓或形成热，DeltaS 是熵值，T 是开尔文温度）进行校正时，预测值接近 15 Pa，与实验确定的值更接近。该共培养物还将乙醇氧化为乙酸，这是比乙酸氧化为 CO(2)更热力学有利的反应。在乙醇氧化过程中，H(2)分压达到高达 200 Pa。直到乙醇被消耗且 H(2)分压降低至 40 至 50 Pa 后才使用乙酸。乙酸利用后，H(2)分压降至约 10 Pa 并保持在那里，表明甲烷菌利用 H(2)的阈值。将乙酸氧化生物的无菌培养物与 Methanobacterium sp. strain THF 或 Methanobacterium thermoautotrophicum DeltaH 的纯培养物组合形成重组乙酸氧化共培养物。在这两种重组共培养物中测量的 H(2)分压与在原始乙酸氧化棒共培养物中测量的分压相似。由于 M. thermoautotrophicum DeltaH 不将甲酸盐用作底物，因此在这种共培养物中，甲酸盐不一定参与种间电子转移。
