General Electric Company, Corporate Research and Development, Schenectady, New York 12301.
Appl Environ Microbiol. 1988 May;54(5):1216-21. doi: 10.1128/aem.54.5.1216-1221.1988.
Clostridium thermocellum produces ethanol, acetate, H(2), and CO(2) as major fermentation products from cellulose and cellobiose. The performance of three strains of this microorganism was studied to assess the potential use in producing ethanol directly from cellulosic fiber. Depending on the bacterial strain, an ethanol/acetate product ratio from 1 to as high as 3 was observed in unstirred cultures. Vigorous stirring during growth resulted in a threefold decrease in the ethanol/acetate ratio. The H(2) content in the unstirred culture broth was three times greater than that in the stirred one. Addition of exogenous H(2) to the gas phase during growth increased the ethanol/acetate ratio much more in the stirred than in the unstirred fermentations. The addition of sufficient H(2) to the gas phase almost relieved the effect of stirring, and the ethanol/acetate ratio approached that in the unstirred condition. Addition of tritium to the gas phase of the culture resulted in the formation of tritiated water (H(2)O), which indicates that C. thermocellum possesses hydrogenase(s) that catalyzes the reverse reaction. The rate of H(2)O formation was about three times higher in the stirred culture than in the unstirred culture. These results demonstrate that the H(2) concentration in the broth plays an important role in the product formation. The H(2) supersaturation present in the unstirred cultures is responsible for the observed effect of stirring. A hydrogen feedback control mechanism regulating the relative concentrations of reduced and oxidized electron carriers is proposed to account for the effect of hydrogen on the metabolite distribution.
热纤梭菌从纤维素和纤维二糖生产乙醇、乙酸、H₂和 CO₂作为主要发酵产物。研究了该微生物的三个菌株的性能，以评估其直接从纤维素纤维生产乙醇的潜力。根据细菌菌株的不同，在未搅拌的培养物中观察到乙醇/乙酸产物比从 1 到高达 3。在生长过程中剧烈搅拌会使乙醇/乙酸比降低三倍。未搅拌培养物中 H₂的含量是搅拌培养物的三倍。在生长过程中向气相中添加外源 H₂会使搅拌发酵中的乙醇/乙酸比增加三倍以上。向气相中添加足够的 H₂几乎可以缓解搅拌的影响，并且乙醇/乙酸比接近未搅拌条件。向培养物的气相中添加氚会形成氚化水（H₂O），这表明热纤梭菌具有氢酶，可催化逆反应。搅拌培养物中 H₂O 的形成速率比未搅拌培养物高约三倍。这些结果表明，发酵液中的 H₂浓度在产物形成中起着重要作用。未搅拌培养物中存在的 H₂过饱和度是搅拌的观察到的影响的原因。提出了一种氢反馈控制机制来调节还原和氧化电子载体的相对浓度，以解释氢对代谢物分布的影响。
