Wang Oumei, Zheng Shiling, Wang Bingchen, Wang Wenjing, Liu Fanghua
Binzhou Medical University, Yantai, Shandong, China.
Key Laboratory of Coastal Biology and Biological Resources Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, Shandong, China.
PeerJ. 2018 Mar 21;6:e4541. doi: 10.7717/peerj.4541. eCollection 2018.
Magnetite-mediated direct interspecies electron transfer (DIET) between and species is increasingly being invoked to explain magnetite stimulation of methane production in anaerobic soils and sediments. Although magnetite-mediated DIET has been documented in defined co-cultures reducing fumarate or nitrate as the electron acceptor, the effects of magnetite have only been inferred in methanogenic systems.
Concentrations of methane and organic acid were analysed with a gas chromatograph and high-performance liquid chromatography, respectively. The concentration of HCl-extractable Fe(II) was determined by the ferrozine method. The association of the defined co-cultures of and with magnetite was observed with transmission electron micrographs.
Magnetite stimulated ethanol metabolism and methane production in defined co-cultures of and ; however, magnetite did not promote methane production in co-cultures initiated with a culture of that could not produce electrically conductive pili (e-pili), unlike the conductive carbon materials that facilitate DIET in the absence of e-pili. Transmission electron microscopy revealed that and were closely associated when magnetite was present, as previously observed in co-cultures. These results show that magnetite can promote DIET between and species, but not as a substitute for e-pili, and probably functions to facilitate electron transfer from the e-pili to .
In summary, the e-pili are necessary for the stimulation of not only , but also methanogenic with magnetite.
越来越多的研究认为，磁铁矿介导的不同物种间直接电子转移（DIET）在厌氧土壤和沉积物中对甲烷生成的刺激作用中发挥着重要作用。尽管在以富马酸盐或硝酸盐作为电子受体的特定共培养体系中已经证实了磁铁矿介导的DIET，但在产甲烷体系中，磁铁矿的作用仍只是推测。
分别使用气相色谱仪和高效液相色谱仪分析甲烷和有机酸的浓度。采用亚铁嗪法测定盐酸可提取铁（II）的浓度。通过透射电子显微镜观察特定的 和 共培养物与磁铁矿的结合情况。
在特定的 和 共培养体系中，磁铁矿刺激了乙醇代谢和甲烷生成；然而，与在缺乏导电菌毛（e - pili）时促进DIET的导电碳材料不同，磁铁矿并不能促进由不能产生导电菌毛的 培养物起始的共培养体系中的甲烷生成。透射电子显微镜显示，当存在磁铁矿时， 和 紧密结合，这与之前在 共培养体系中观察到的情况一致。这些结果表明，磁铁矿可以促进 和 之间的DIET，但不能替代e - pili，其作用可能是促进电子从e - pili转移到 。
总之，e - pili不仅对 ，而且对磁铁矿刺激产甲烷的 都是必需的。
