Electron transport through electrically conductive nanofilaments in Rhodopseudomonas palustris strain RP2
Electronic dialogue between proteins is expected to be a key component of charge transport at the microbe–mineral interface (MMI) and requires complex structures. Microbial nanofilaments are one such structure produced in energetically engineered environments. These nanostructures consist of natural protein electronic conduits which can target the microbe–mineral interface and facilitate charge transport over a distance. Nanofilaments are phylogenetically diverse inducible extracellular appendages, and have the potential to serve as organic electronic conductors. However, recent investigations on such microbial nanofilaments have been confined to a few bacterial genera such as Geobacter, Shewanella and Synechocystis. Here, we report the evidence for longitudinal electron transport through inducible nanofilaments produced by another genus, the metabolically versatile photosynthetic, iron(III) respiring bacterium Rhodopseudomonas palustris strain RP2, in photic, iron(III) oxide-rich environments. In contrast, chemosynthetic dark-grown anoxic cells are weak in their ability to reduce ferric-oxide and no longer produce extracellular structures. Independent evaluation techniques illustrate the induction of extracellular filaments and their electrical properties. Scanning probe and nanofabricated electrode measurements provide conclusive evidence for the occurrence of direct charge transfer along the length and radius of nanofilaments from strain RP2. These findings not only expand our knowledge of the range of bacteria known to produce nanofilaments but also provide further research opportunities in the field of bionanotechnology, sustainable remediation (bioelectrochemical remediation systems) in contaminated sites (petroleum hydrocarbons) and MMI process at photic environments.