Lovley's group originally proposed Geobacter's conductive nanowires were PilA-based type IV pili ('e-pili')

In 2005, Reguera, McCarthy, Mehta, Nicoll, Tuominen and Lovley published "Extracellular electron transfer via microbial nanowires" (Nature 435, 1098–1101), proposing that the type-IV pili of Geobacter sulfurreducens — filaments assembled from the PilA pilin monomer — conduct electrons over long range and so serve as the organism's conductive "nanowires." The original evidence was conductive-tip atomic force microscopy: a later review co-authored by Derek Lovley himself (Lovley & Walker, Frontiers in Microbiology, 2019) recounts that conductive-AFM "revealed that the pili were electrically conductive with an ohmic-like (current = voltage/resistance) linear current-voltage response," leading to the conclusion that "the pili of G. sulfurreducens function as a 'microbial nanowire' for long-range extracellular electron transfer."

This PilA-based model — later branded "e-pili" (electrically conductive pili) — was the standing consensus for roughly a decade and a half, and it is the model that subsequent cryo-EM structural work (claim-geobacter-conductive-filaments-are-omcs-cytochrome-polymers, claim-geobacter-pili-are-secretory-pseudopili-not-nanowires) directly contradicts. It is a distinct proposed mechanism from the sulfur-ligated nickel wire reported for cable bacteria (claim-cable-bacteria-conduct-through-nickel-protein-wire): a different organism, and a different candidate for what carries the current. Both belong to the broader phenomenon of extracellular electron transfer.