Identification of a Pathway for Electron Uptake in Shewanella oneidensis

Data for figures for "Identification of a Pathway for Electron Uptake in Shewanella oneidensis"

Abstract

Extracellular electron transfer (EET) could enable electron uptake into microbial metabolism for the synthesis of complex, energy dense organic molecules from CO2 and renewable electricity1-6 . Theoretically EET could do this with an efficiency comparable to H2-oxidation7,8 but without the need for a volatile intermediate and the problems it causes for scale up9. However, significant gaps remain in understanding the mechanism and genetics of electron uptake. For example, studies of electron uptake in electroactive microbes have shown a role for the Mtr EET complex in the electroactive microbe Shewanella oneidensis MR-110-14, though there is substantial variation in the magnitude of effect deletion of these genes has depending on the terminal electron acceptor used. This speaks to the potential for novel and/or differentially utilized genes involved in electron uptake. To address this, we screened gene disruption mutants for 3,667 genes, representing ≈ 99% of all non-essential genes, from the S. oneidensiswhole genome knockout collection using a redox dye oxidation assay. Confirmation of electron uptake using electrochemical testing allowed us to identify five genes from S. oneidensis that are indispensable for electron uptake from a cathode. Knockout of each gene eliminates extracellular electron uptake, yet in four of the five cases produces no significant defect in electron donation to an anode. This result highlights both distinct electron uptake components and an electronic connection between aerobic and anaerobic electron transport chains that allow electrons from the reversible EET machinery to be coupled to different respiratory processes in S. oneidensis. Homologs to these genes across many different genera suggesting that electron uptake by EET coupled to respiration could be widespread. These gene discoveries provide a foundation for: studying this phenotype in exotic metal-oxidizing microbes, genetic optimization of electron uptake in S. oneidensis; and genetically engineering electron uptake into a highly tractable host like E. coli to complement recent advances in synthetic CO2 fixation15.

《奥奈达希瓦氏菌（Shewanella oneidensis）电子摄取途径的鉴定》一文的配图数据集

摘要

胞外电子传递（Extracellular electron transfer, EET）可介导电子摄入微生物代谢过程，从而以二氧化碳（CO₂）和可再生电力为原料合成复杂且高能量密度的有机分子[1-6]。从理论上来说，EET实现该过程的效率可与氢氧化（H₂-oxidation）相当[7,8]，且无需使用挥发性中间产物，也不会出现其带来的规模化放大难题[9]。然而，目前学界对电子摄取的机制与遗传调控机制仍存在诸多认知空白。例如，针对电活性微生物的电子摄取研究表明，Mtr EET复合物（Mtr EET complex）在电活性微生物奥奈达希瓦氏菌（Shewanella oneidensis）MR-1菌株的电子摄取过程中发挥作用[10-14]，但删除这些基因所产生的影响程度会因所使用的末端电子受体不同而存在显著差异。这提示我们，可能存在参与电子摄取的新型基因或差异化利用的基因。为解决这一问题，本研究利用氧化还原染料氧化分析法，从奥奈达希瓦氏菌全基因组敲除文库中筛选了3667个基因的基因敲除突变体，覆盖该菌约99%的非必需基因。通过电化学测试验证电子摄取能力后，我们成功鉴定出奥奈达希瓦氏菌中5个对从阴极摄取电子不可或缺的基因。删除任意一个该类基因都会完全阻断胞外电子摄取，但其中4个基因的缺失并不会显著影响向阳极传递电子的能力。该研究结果不仅揭示了独特的电子摄取组分，还阐明了有氧与厌氧电子传递链之间的电子连接机制，使得可逆EET系统获取的电子可与奥奈达希瓦氏菌内的不同呼吸过程相偶联。这些基因的同源序列广泛存在于多个不同的菌属中，这表明通过EET与呼吸作用偶联实现电子摄取的现象可能广泛存在。此次发现的这些基因可为后续研究奠定基础：包括在特殊的金属氧化微生物中研究该表型、对奥奈达希瓦氏菌的电子摄取能力进行遗传优化，以及通过基因工程手段将电子摄取模块引入大肠杆菌（Escherichia coli, E. coli）这类易于操作的模式宿主中，以辅助近期合成CO₂固定技术的研究进展[15]。