Charge Injection and Inter-Fiber Electrical Conduction in Cable Bacteria

Cable bacteria are multicellular microorganisms capable of charge transport over centimeterscale distances through a network of conductive fibers embedded in the periplasm. Understanding the charge injection mechanism in cable bacteria is essential to form a complete picture of their long-distance charge transport, and a crucial step for their application in bio-based electronics. To this aim, we fabricated ”crosses” of two filaments, either native bacteria or extracted fiber skeletons, placed one on top of each other. By probing charge transport both through single cables and in cross-cable configurations, i.e., with current flowing from one filament to the other, it is possible to isolate the charge injection contribution. The results indicate that charge transfer between two contacting fibers is possible, albeit with increased resistance. We characterized the crosses at different temperatures, from 300 down to 50 K, observing thermally activated Arrhenius behavior both for single cables and crossconduction.The corresponding activation energy for cable-to-cable transport ranged from 15 to 40 meV, slightly smaller than that of individual cable bacteria filaments. We conclude that charge injection into the fibers must rely on the same mechanism of charge transport along the fibers. A structural model of the fibers is proposed in which the conductive channels are embedded in a protein matrix but can locally reach the surface of the fibers, where they establish electrical contact with the external environment.电缆细菌（cable bacteria）是一类多细胞微生物，可通过周质内嵌入的导电纤维网络实现厘米级距离的电荷传输。阐明电缆细菌的电荷注入机制，既是完整解析其长距离电荷传输全貌的核心前提，也是推动其在生物基电子学领域应用的关键环节。为此，我们制备了由两根丝状体构成的"十字结构"：样品可选用天然细菌或提取得到的纤维骨架，将二者相互叠放。通过分别探测单根电缆细菌的电荷传输，以及跨电缆构型（即电流从一根丝状体流向另一根的传导模式）下的电荷传输，我们得以分离出电荷注入的贡献占比。实验结果显示，两根接触的纤维之间可发生电荷转移，尽管其传输电阻会有所升高。我们在300 K至50 K的宽温度区间内对该十字结构进行了表征，结果发现单根电缆细菌与跨电缆传导均表现出热激活的阿伦尼乌斯（Arrhenius）行为。跨电缆传输对应的活化能介于15 meV至40 meV之间，略低于单根电缆细菌丝状体的活化能。综上我们认为，向纤维内注入电荷的过程，必然依赖于沿纤维进行电荷传输的同一核心机制。我们提出了一种纤维结构模型：导电通道嵌入于蛋白质基质中，但可局部抵达纤维表面，借此与外部环境建立电接触。