The discovery of electrically conductive bacterial nanowires from a broad range of microbes provides completely new insights into microbial physiology. Shewanella oneidensis strain MR-1, a dissimilatory metal-reducing bacterium, produces extracellular bacterial nanowires up to tens of micrometers long, with a lateral dimension of ~10 nm. The Shewanella bacterial nanowires are efficient electrical conductors as revealed by scanning probe techniques such as CP-AFM and STM.
Direct electrical transport measurements along Shewanella nanowires reveal a measured nanowire resistivity on the order of 1 Ω∙cm. With electron transport rates up to 109/s at 100 mV, bacterial nanowires can serve as a viable microbial strategy for extracellular electron transport. By modulating the nanowire conductance in NW-FET configurations and CP-AFM measurements on nanowires coupled to different electrode materials, it has been found that Shewanella nanowires behave as a gateable p-type semiconductor with a Fermi level close to 5.3 eV. This finding further suggests that Shewanella nanowires may serve as electronic cables for efficient energy distribution and electronic signal exchange within microbial communities.
Two separate AFM experiments, which are real-time elastic modulus mapping using torsional harmonic cantilevers and conventional AFM nanoindentation, mutually confirm that the elastic modulus of Shewanella nanowires is on the order of 1 GPa, with no significant variations in local elasticity along individual nanowires. With electrical properties comparable to those of moderately doped inorganic semiconductors and elasticity close to polymeric materials, bacterial nanowires may represent a new class of functional bionanomaterials that will potentially be building blocks for bionanoelectronics and flexible nanoelectronics
