Bacterial nanowires (also known as microbial nanowires) are electrically conductive appendages produced by a number of bacteria most notably from (but not exclusive to) the Geobacter and Shewanella genera. Conductive nanowires have also been confirmed in the oxygenic cyanobacterium Synechocystis PCC6803 and a thermophilic, methanogenic coculture consisting of Pelotomaculum thermopropionicum and Methanothermobacter thermoautotrophicus.
Geobacter nanowires are modified pili, which are used to establish connections to terminal electron acceptors. Species of the genus Geobacter use nanowires to transfer electrons to extracellular electron acceptors (such as Fe(III) oxides). This function was discovered through the examination of mutants, whose pili could attach to the iron, but would not reduce it.
However, Shewanella nanowires are not pili, but extensions of the outer membrane that contain the decaheme outer membrane cytochromes MtrC and OmcA. The reported presence of outer membrane cytochromes, and lack of conductivity in nanowires from the MtrC and OmcA-deficient mutant directly support the proposed multistep hopping mechanism for electron transport through Shewanella nanowires.
Additionally, nanowires can facilitate long-range electron transfer across thick biofilm layers. By connecting to other cells above them, nanowires allow bacteria located in anoxic conditions to still use oxygen as their terminal electron acceptor. For example, organisms in the genus Shewanella have been observed to form electrically conductive nanowires in response to electron-acceptor limitation.
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Implications and Potential Applications
Biologically it is unclear what is implied by the existence of bacterial nanowires. Nanowires may function as conduits for electron transport between different members of a microbial community.
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