Cord-Ruwisch R, Lovley DR, Schink B
Biotechnology, Murdoch University, Perth, Western Australia 6150, Australia.
Appl Environ Microbiol. 1998 Jun;64(6):2232-6. doi: 10.1128/AEM.64.6.2232-2236.1998.
Pure cultures of Geobacter sulfurreducens and other Fe(III)-reducing bacteria accumulated hydrogen to partial pressures of 5 to 70 Pa with acetate, butyrate, benzoate, ethanol, lactate, or glucose as the electron donor if electron release to an acceptor was limiting. G. sulfurreducens coupled acetate oxidation with electron transfer to an anaerobic partner bacterium in the absence of ferric iron or other electron acceptors. Cocultures of G. sulfurreducens and Wolinella succinogenes with nitrate as the electron acceptor degraded acetate efficiently and grew with doubling times of 6 to 8 h. The hydrogen partial pressures in these acetate-degrading cocultures were considerably lower, in the range of 0.02 to 0.04 Pa. From these values and the concentrations of the other reactants, it was calculated that in this cooperation the free energy change available to G. sulfurreducens should be about -53 kJ per mol of acetate oxidized, assuming complete conversion of acetate to CO2 and H2. However, growth yields (18.5 g of dry mass per mol of acetate for the coculture, about 14 g for G. sulfurreducens) indicated considerably higher energy gains. These yield data, measurement of hydrogen production rates, and calculation of the diffusive hydrogen flux indicated that electron transfer in these cocultures may not proceed exclusively via interspecies hydrogen transfer but may also proceed through an alternative carrier system with higher redox potential, e.g., a c-type cytochrome that was found to be excreted by G. sulfurreducens into the culture fluid. Syntrophic acetate degradation was also possible with G. sulfurreducens and Desulfovibrio desulfuricans CSN but only with nitrate as electron acceptor. These cultures produced cell yields of 4.5 g of dry mass per mol of acetate, to which both partners contributed at about equal rates. These results demonstrate that some Fe(III)-reducing bacteria can oxidize organic compounds under Fe(III) limitation with the production of hydrogen, and they provide the first example of rapid acetate oxidation via interspecies electron transfer at moderate temperature.
如果向受体的电子释放受到限制，以乙酸盐、丁酸盐、苯甲酸盐、乙醇、乳酸盐或葡萄糖作为电子供体时，硫还原地杆菌（Geobacter sulfurreducens）和其他还原铁（III）的细菌纯培养物会将氢气积累到5至70帕的分压。在没有三价铁或其他电子受体的情况下，硫还原地杆菌将乙酸氧化与电子转移耦合到厌氧伙伴细菌。以硝酸盐作为电子受体时，硫还原地杆菌和琥珀酸沃林氏菌（Wolinella succinogenes）的共培养物能有效降解乙酸盐，并以6至8小时的倍增时间生长。在这些降解乙酸盐的共培养物中，氢气分压要低得多，在0.02至0.04帕的范围内。根据这些数值以及其他反应物的浓度计算得出，假设乙酸盐完全转化为二氧化碳和氢气，在这种合作中，硫还原地杆菌每氧化1摩尔乙酸盐可利用的自由能变化约为-53千焦。然而，生长产量（共培养物每摩尔乙酸盐产生18.5克干重，硫还原地杆菌约为14克）表明能量增益要高得多。这些产量数据、氢气产生速率的测量以及扩散氢通量的计算表明，这些共培养物中的电子转移可能并非仅通过种间氢转移进行，还可能通过具有更高氧化还原电位的替代载体系统进行，例如发现硫还原地杆菌分泌到培养液中的c型细胞色素。硫还原地杆菌和脱硫脱硫弧菌（Desulfovibrio desulfuricans CSN）也能进行乙酸盐的互营降解，但仅以硝酸盐作为电子受体。这些培养物每摩尔乙酸盐产生4.5克干重的细胞产量，两个伙伴的贡献速率大致相等。这些结果表明，一些还原铁（III）的细菌在铁（III）受限的情况下可以氧化有机化合物并产生氢气，并且它们提供了在中等温度下通过种间电子转移快速氧化乙酸盐的首个实例。
