Structures, Compositions, and Activities of Live Shewanella Biofilms Formed on Graphite Electrodes in Electrochemical Flow Cells
Structures, Compositions, and Activities of Live Shewanella Biofilms Formed on Graphite Electrodes in Electrochemical Flow Cells
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DOI：
10.1128/aem.00903-17
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发表时间：
2017-09-01
影响因子：
4.4
通讯作者：
Watanabe, Kazuya
中科院分区：
文献类型：
--
作者：
Kitayama, Miho;Koga, Ryota;Watanabe, Kazuya
在底部装有石墨工作电极（WE）的电化学流动电池中接种表达厌氧荧光蛋白的奈氏希瓦氏菌MR-1，在电解流动条件下，在+/- 0.4 V和0 V的WE电位（相对于标准氢电极）下，随着时间的推移，在WE上观察生物膜的形成。电化学分析表明，+/- 0.4 v生物膜中存在独特的电子转移机制。显微镜分析显示，与好氧生物膜相比，产电流生物膜（+/- 0.4 V）薄而平坦（厚度接近10 μ m），细胞均匀而密集地分布在生物膜中。相反，细胞在0 V形成的生物膜中分布不均匀。原位荧光染色和生物膜恢复实验表明，+/- 0.4 V生物膜中胞外多糖（eps）的数量远少于好氧和0-V生物膜，表明希瓦氏菌细胞在+/- 0.4 V流动条件下抑制了eps的产生。我们认为希瓦氏菌细胞感知电极电位并调节生物膜的结构和组成以有效地将电子转移到电极上。微生物燃料电池（MFCs）在污水处理中的节能应用前景广阔。由于在废水水平流动条件下，这些mfc中的生物膜微生物产生电流，因此了解水流条件下生物膜形成和电流产生的机制非常重要。尽管已经做了大量的工作来分析模型外电细菌（如希瓦氏菌）产生电流的分子机制，但关于水流条件下随着时间的推移形成电流的生物膜的信息有限。本研究开发了电化学流动电池，并利用它来研究水流条件下产生电流的生物膜的电化学和结构特征。我们展示了成熟生物膜积极产生电流的独特特征，为在希瓦氏菌生物膜中寻找尚未发现的电流产生机制创造了机会。此外，本研究提供的信息对于试图开发适用于废水处理mfc的阳极结构的研究人员是有用的。
An electrochemical flow cell equipped with a graphite working electrode (WE) at the bottom was inoculated with Shewanella oneidensis MR-1 expressing an anaerobic fluorescent protein, and biofilm formation on the WE was observed over time during current generation at WE potentials of +/- 0.4 and 0 V (versus standard hydrogen electrodes), under electrolyte-flow conditions. Electrochemical analyses suggested the presence of unique electron-transfer mechanisms in the +/- 0.4-V biofilm. Microscopic analyses revealed that, in contrast to aerobic biofilms, current-generating biofilm (at +/- 0.4 V) was thin and flat (similar to 10 mu m in thickness), and cells were evenly and densely distributed in the biofilm. In contrast, cells were unevenly distributed in biofilm formed at 0 V. In situ fluorescence staining and biofilm recovery experiments showed that the amounts of extracellular polysaccharides (EPSs) in the +/- 0.4-V biofilm were much smaller than those in the aerobic and 0-V biofilms, suggesting that Shewanella cells suppress the production of EPSs at +/- 0.4 V under flow conditions. We suggest that Shewanella cells perceive electrode potentials and modulate the structure and composition of biofilms to efficiently transfer electrons to electrodes.IMPORTANCE A promising application of microbial fuel cells (MFCs) is to save energy in wastewater treatment. Since current is generated in these MFCs by biofilm microbes under horizontal flows of wastewater, it is important to understand the mechanisms for biofilm formation and current generation under water-flow conditions. Although massive work has been done to analyze the molecular mechanisms for current generation by model exoelectrogenic bacteria, such as Shewanella oneidensis, limited information is available regarding the formation of current-generating biofilms over time under water-flow conditions. The present study developed electrochemical flow cells and used them to examine the electrochemical and structural features of current-generating biofilms under water-flow conditions. We show unique features of mature biofilms actively generating current, creating opportunities to search for as-yet-undiscovered current-generating mechanisms in Shewanella biofilms. Furthermore, information provided in the present study is useful for researchers attempting to develop anode architectures suitable for wastewater treatment MFCs.