the mystery of conductive bacterial nanowires

PNAS | Bacterial nanowires are extracellular appendages that may facilitate electron transport between and among diverse species, including the metal-reducing bacteria, Shewanella oneidensis MR-1. Although several biological assays have provided results consistent with bacterial nanowire conductivity, until now researchers had not found direct evidence of electron transport along nanowires. Mohamed El-Naggar et al. used nanofabricated electrodes and conducting probe atomic force microscopy to measure electron transport along individual S. oneidensis MR-1 nanowires. The researchers found that the bacterial nanowires were electrically conductive along micron length scales, and estimate that the nanowires’ current capacity is sufficient to discharge the cell’s respiratory electrons to terminal electron receptors during extracellular electron transport. Bacterial mutants deficient in genes necessary for electron transport produced appendages that were morphologically consistent with wild type nanowires, but were nonconductive. The study suggests that bacteria, the oldest organisms on the planet, may use integrated circuitry for energy distribution, a hypothesis that challenges traditional understanding of extracellular electron transport in microbial communities, according to the authors. — J.M.