Elshahed M S, McInerney M J
Department of Botany and Microbiology, University of Oklahoma, Norman 73019, USA.
Appl Environ Microbiol. 2001 Dec;67(12):5520-5. doi: 10.1128/AEM.67.12.5520-5525.2001.
The anaerobic bacterium Syntrophus aciditrophicus metabolized benzoate in pure culture in the absence of hydrogen-utilizing partners or terminal electron acceptors. The pure culture of S. aciditrophicus produced approximately 0.5 mol of cyclohexane carboxylate and 1.5 mol of acetate per mol of benzoate, while a coculture of S. aciditrophicus with the hydrogen-using methanogen Methanospirillum hungatei produced 3 mol of acetate and 0.75 mol of methane per mol of benzoate. The growth yield of the S. aciditrophicus pure culture was 6.9 g (dry weight) per mol of benzoate metabolized, whereas the growth yield of the S. aciditrophicus-M. hungatei coculture was 11.8 g (dry weight) per mol of benzoate. Cyclohexane carboxylate was metabolized by S. aciditrophicus only in a coculture with a hydrogen user and was not metabolized by S. aciditrophicus pure cultures. Cyclohex-1-ene carboxylate was incompletely degraded by S. aciditrophicus pure cultures until a free energy change (DeltaG') of -9.2 kJ/mol was reached (-4.7 kJ/mol for the hydrogen-producing reaction). Cyclohex-1-ene carboxylate, pimelate, and glutarate transiently accumulated at micromolar levels during growth of an S. aciditrophicus pure culture with benzoate. High hydrogen (10.1 kPa) and acetate (60 mM) levels inhibited benzoate metabolism by S. aciditrophicus pure cultures. These results suggest that benzoate fermentation by S. aciditrophicus in the absence of hydrogen users proceeds via a dismutation reaction in which the reducing equivalents produced during oxidation of one benzoate molecule to acetate and carbon dioxide are used to reduce another benzoate molecule to cyclohexane carboxylate, which is not metabolized further. Benzoate fermentation to acetate, CO(2), and cyclohexane carboxylate is thermodynamically favorable and can proceed at free energy values more positive than -20 kJ/mol, the postulated minimum free energy value for substrate metabolism.
厌氧细菌嗜酸互营杆菌（Syntrophus aciditrophicus）在没有利用氢气的伙伴或末端电子受体的情况下，能在纯培养物中代谢苯甲酸盐。嗜酸互营杆菌的纯培养物每摩尔苯甲酸盐产生约0.5摩尔环己烷羧酸盐和1.5摩尔乙酸盐，而嗜酸互营杆菌与利用氢气的产甲烷菌亨氏甲烷螺菌（Methanospirillum hungatei）的共培养物每摩尔苯甲酸盐产生3摩尔乙酸盐和0.75摩尔甲烷。嗜酸互营杆菌纯培养物的生长产量为每代谢摩尔苯甲酸盐6.9克（干重），而嗜酸互营杆菌 - 亨氏甲烷螺菌共培养物的生长产量为每摩尔苯甲酸盐11.8克（干重）。环己烷羧酸盐仅在与利用氢气的微生物共培养时被嗜酸互营杆菌代谢，而在嗜酸互营杆菌纯培养物中不被代谢。环己 - 1 - 烯羧酸盐被嗜酸互营杆菌纯培养物不完全降解，直到达到 -9.2 kJ/mol的自由能变化（ΔG'）（产氢反应为 -4.7 kJ/mol）。在嗜酸互营杆菌利用苯甲酸盐的纯培养物生长过程中，环己 - 1 - 烯羧酸盐、庚二酸和戊二酸以微摩尔水平短暂积累。高氢气（10.1 kPa）和乙酸盐（60 mM）水平抑制嗜酸互营杆菌纯培养物对苯甲酸盐的代谢。这些结果表明，在没有利用氢气的微生物存在的情况下，嗜酸互营杆菌对苯甲酸盐的发酵通过歧化反应进行，其中一个苯甲酸盐分子氧化为乙酸盐和二氧化碳过程中产生的还原当量用于将另一个苯甲酸盐分子还原为环己烷羧酸盐，而环己烷羧酸盐不再进一步代谢。苯甲酸盐发酵生成乙酸盐、CO₂ 和环己烷羧酸盐在热力学上是有利的，并且可以在比 -20 kJ/mol（假定的底物代谢最小自由能值）更正的自由能值下进行。
