Lampa-Pastirk Sanela, Veazey Joshua P, Walsh Kathleen A, Feliciano Gustavo T, Steidl Rebecca J, Tessmer Stuart H, Reguera Gemma
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing MI 48824, USA.
Department of Physics and Astronomy, Michigan State University, East Lansing MI 48824, USA.
Sci Rep. 2016 Mar 24;6:23517. doi: 10.1038/srep23517.
The bacterium Geobacter sulfurreducens requires the expression of conductive protein filaments or pili to respire extracellular electron acceptors such as iron oxides and uranium and to wire electroactive biofilms, but the contribution of the protein fiber to charge transport has remained elusive. Here we demonstrate efficient long-range charge transport along individual pili purified free of metal and redox organic cofactors at rates high enough to satisfy the respiratory rates of the cell. Carrier characteristics were within the orders reported for organic semiconductors (mobility) and inorganic nanowires (concentration), and resistivity was within the lower ranges reported for moderately doped silicon nanowires. However, the pilus conductance and the carrier mobility decreased when one of the tyrosines of the predicted axial multistep hopping path was replaced with an alanine. Furthermore, low temperature scanning tunneling microscopy demonstrated the thermal dependence of the differential conductance at the low voltages that operate in biological systems. The results thus provide evidence for thermally activated multistep hopping as the mechanism that allows Geobacter pili to function as protein nanowires between the cell and extracellular electron acceptors.
嗜硫还原地杆菌需要表达导电蛋白细丝或菌毛来呼吸细胞外电子受体，如氧化铁和铀，并连接电活性生物膜，但蛋白质纤维对电荷传输的贡献仍不清楚。在这里，我们展示了沿着不含金属和氧化还原有机辅因子的纯化单根菌毛进行高效的长程电荷传输，其速率足以满足细胞的呼吸速率。载流子特性在有机半导体（迁移率）和无机纳米线（浓度）报道的范围内，电阻率在中等掺杂硅纳米线报道的较低范围内。然而，当预测的轴向多步跳跃路径中的一个酪氨酸被丙氨酸取代时，菌毛电导率和载流子迁移率降低。此外，低温扫描隧道显微镜显示了在生物系统中运行的低电压下微分电导的热依赖性。因此，这些结果为热激活多步跳跃提供了证据，证明这是嗜硫还原地杆菌菌毛在细胞和细胞外电子受体之间充当蛋白质纳米线的机制。
