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Electron and Proton Flux for Carbon Dioxide Reduction in Methanosarcina barkeri During Direct Interspecies Electron Transfer

机译:电子和质子通量用于直接种间电子转移期间甲烷甲烷八叠球菌的二氧化碳还原

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摘要

Direct interspecies electron transfer (DIET) is important in diverse methanogenic environments, but how methanogens participate in DIET is poorly understood. Therefore, the transcriptome of Methanosarcina barkeri grown via DIET in co-culture with Geobacter metallireducens was compared with its transcriptome when grown via H2 interspecies transfer (HIT) with Pelobacter carbinolicus. Notably, transcripts for the F420H2 dehydrogenase, Fpo, and the heterodisulfide reductase, HdrABC, were more abundant during growth on DIET. A model for CO2 reduction was developed from these results in which electrons delivered to methanophenazine in the cell membrane are transferred to Fpo. The external proton gradient necessary to drive the otherwise thermodynamically unfavorable reverse electron transport for Fpo-catalyzed F420 reduction is derived from protons released from G. metallireducens metabolism. Reduced F420 is a direct electron donor in the carbon dioxide reduction pathway and also serves as the electron donor for the proposed HdrABC-catalyzed electron bifurcation reaction in which reduced ferredoxin (also required for carbon dioxide reduction) is generated with simultaneous reduction of CoM-S-S-CoB. Expression of genes for putative redox-active proteins predicted to be localized on the outer cell surface was higher during growth on DIET, but further analysis will be required to identify the electron transfer route to methanophenazine. The results indicate that the pathways for electron and proton flux for CO2 reduction during DIET are substantially different than for HIT and suggest that gene expression patterns may also be useful for determining whether Methanosarcina are directly accepting electrons from other extracellular electron donors, such as corroding metals or electrodes.
机译:直接种间电子转移(DIET)在不同的产甲烷环境中很重要,但是产甲烷菌如何参与DIET的了解却很少。因此,将通过DIET与金属还原杆菌共培养的通过甲烷生长的甲烷甲烷八叠球菌的转录组与通过与Carlopolus的H2种间转移(HIT)进行生长时的转录组进行了比较。值得注意的是,在DIET上生长期间,F420H2脱氢酶Fpo和杂二硫键还原酶HdrABC的转录物更加丰富。从这些结果中发展出了一种减少二氧化碳的模型,在该模型中,传递至细胞膜中甲氧吩嗪的电子被转移至Fpo。驱动从另外的热力学上不利的逆向电子传输以促进Fpo催化的F420还原所必需的外部质子梯度来自金属还原还原杆菌代谢的质子。还原的F420是二氧化碳还原途径中的直接电子给体,也可作为拟议的HdrABC催化的电子分叉反应的电子给体,在该反应中,还原的铁氧还蛋白(也是二氧化碳还原所必需的)同时还原CoM-SS -CoB。在DIET上生长期间,预计位于细胞外表面的假定氧化还原活性蛋白的基因表达较高,但需要进一步分析以鉴定电子转移至甲氧吩嗪的途径。结果表明,DIET期间电子和质子通量减少CO2的途径与HIT的途径大不相同,这表明基因表达模式还可用于确定甲烷八叠球菌是否直接接受其他细胞外电子供体(如腐蚀金属)的电子或电极。

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