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Bacterial nanowires
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.〔G. Reguera et al., Nature 435, 1098 (2005)〕〔Y. A. Gorby et al., Proceedings of the National Academy of Sciences of the United States of America 103, 11358 (2006).〕 Conductive nanowires have also been confirmed in the oxygenic cyanobacterium ''Synechocystis'' PCC6803 and a thermophilic, methanogenic coculture consisting of ''Pelotomaculum thermopropionicum'' and ''Methanothermobacter thermoautotrophicus''.〔
==Physiology==
''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).〔Reguera et al. 2005. Extracellular electron transfer via microbial nanowires. Nature 435:1098-1101 .〕 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.〔 Pirbadian et al. 2014. Shewanella oneidensis MR-1 nanowires are outer membrane and periplasmic extensions of the extracellular electron transport components. Proc Natl Acad Sci USA doi:10.1073/pnas.1410551111〕 The reported presence of outer membrane cytochromes, and lack of conductivity in nanowires from the MtrC and OmcA-deficient mutant〔El-Naggar et al. 2010. Electrical transport along bacterial nanowires from Shewanella oneidensis MR-1. Proc Natl Acad Sci USA doi:10.1073/pnas.1004880107〕 directly support the proposed multistep hopping mechanism for electron transport through ''Shewanella'' nanowires.〔Pirbadian S., El-Naggar M.Y., 2012. Multistep hopping and extracellular charge transfer in microbial redox chains. Phys Chem Chem Phys doi:10.1039/C2CP41185G〕〔Polizzi NF, et al., 2012. Physical constraints on charge transport through bacterial nanowires. Faraday Discuss. DOI: 10.1039/C1FD00098E〕〔Strycharz-Glaven SM, et al., 2011. On the electrical conductivity of microbial nanowires and biofilms. Energy Environ Sci 4:4366–4379. DOI: 10.1039/C1EE01753E〕
Additionally, nanowires can facilitate long-range electron transfer across thick ''biofilm'' layers.〔Reguera et al. 2006. Biofilm and nanowire production leads to increased current in Geobacter sulfurreducens fuel cells. Appl. Environ. Microbiol. 72:7345-8.〕 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.〔Gorby et al. 2006. Electrically conductive bacterial nanowires produced by Shewanella oneidensis strain MR-1 and other microorganisms. Proc Natl Acad Sci USA 103(30):11358-63.〕
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