Mechanisms of long-distance extracellular electron transfer of metal-reducing bacteria mediated by nanocolloidal semiconductive iron oxides
Mechanisms of long-distance extracellular electron transfer of metal-reducing bacteria mediated by nanocolloidal semiconductive iron oxides
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DOI：
10.1039/c3ta01672b
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发表时间：
2013-01-01
影响因子：
11.9
通讯作者：
Hashimoto, Kazuhito
中科院分区：
文献类型：
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作者：
Nakamura, Ryuhei;Kai, Fumiyoshi;Hashimoto, Kazuhito
虽然纳米晶Fe（III）氧化物在天然矿物中大量存在，但很少有研究从生物学性质的角度来关注其生物学意义。为了研究铁（III）氧化物在微生物呼吸活动中的作用，我们在电化学电池中培养了铁（III）还原菌Shewanella loihica PV-4，并研究了细胞表面相关的铁氧化物纳米胶体对细胞外电子传递（EET）效率的影响。发现当将α-Fe 2 O3或α-FeOOH补充到细胞培养物中时，呼吸电流大大改善（超过40倍）。相比之下，在添加Fe 3 O 4和γ-Fe 2 O3之后，仅观察到小的改善（小于4倍）。希瓦氏菌细胞外膜C型细胞色素（c-Cyts）的中点电位接近于α-Fe_2O_3和α-FeOOH的导带边缘，而γ-Fe_2O_3和Fe_3O_4存在较大的能量分离。这些观察结果支持最近提出的细菌长距离EET模型（R。中村等人，Angew.化学成分：国际版，2009，48，508-511），其中c-Cyt充当纳米胶体之间的电连接，允许细胞群利用荧光素介导的电子跳跃。外膜c-Cyts的突变实验和相对于负载胶体的量形成导电网络的明确渗滤行为也提供了对该模型的支持。因此，由纳米胶体介导的EET突出了微生物利用基于电化学的呼吸活动的能力。
Although nanocrystalline Fe(III) oxides are abundant in natural minerals, few studies have noticed their biological significance from the view point of semiconductive properties. To examine the roles of semiconductive Fe(III) oxides in the respiratory activity of microorganisms, we cultured the Fe(III)-reducing bacterium Shewanella loihica PV-4 in an electrochemical cell and examined the influence of cell surface-associated Fe-oxide nanocolloids on the extracellular electron transfer (EET) efficiency. It was found that the respiratory current was greatly improved (over 40 fold) when alpha-Fe2O3 or alpha-FeOOH was supplemented into the cell cultures. In contrast, only a small improvement (less than 4 fold) was observed after the addition of Fe3O4 and gamma-Fe2O3. It was also found that the outer-membrane c-type cytochromes (c-Cyts) of Shewanella cells had a midpoint potential close to the conduction-band edge of alpha-Fe2O3 and alpha-FeOOH, whereas a large energy separation existed for gamma-Fe2O3 and Fe3O4. These observations support the recently proposed model for bacterial long-distance EET (R. Nakamura, et al., Angew. Chem., Int. Ed., 2009, 48, 508-511), in which c-Cyts serve as electrical linkages between nanocolloids, allowing the cell population to exploit semiconductor-mediated electron-hopping. Support for this model was also provided by the mutational experiments of outer-membrane c-Cyts and the clear percolation behavior on the formation of conductive networks with respect to the amount of loaded colloids. Thus the EET mediated by semiconductive nanocolloids highlighted the microbial ability to take advantage of semiconductor-based electrochemistry for respiratory activities.