There is a debate whether Geobacter sulfurreducens produces electrically conductive pili (e-pili) from its pilin monomer, PilA, a protein encoded by gene GSU 1496. G. sulfurreducens assembly of the PilA into e-pili was proposed over a decade ago (Reguera et al., 2005). As detailed below, many subsequent studies have provided additional data consistent with this concept (Figure 1). However, Gu et al. have recently concluded that G. sulfurreducens does not express e-pili from PilA (Gu et al., 2021).

This is not a controversy over small details of the physiology of one microbe. Geobacter species play an important role in natural environments and biotechnologies. For example, Geobacter species are typically abundant in soils and sediments in which Fe (III) oxide reduction has a significant impact on the biogeochemical cycling of carbon, nutrients, and trace metals as well as in bioremediation (Lovley et al., 2011; Reguera and Kashefi, 2019; Lovley and Holmes, 2022). Geobacter species are also often abundant in soils and anaerobic digesters in which direct interspecies electron transfer (DIET) appears to be an important mechanism for methane production (Zhao et al., 2020; Lovley and Holmes, 2022). Geobacter and closely related species are often enriched on the anodes of electrodes harvesting electricity from organic matter and G. sulfurreducens generates the highest current densities of all known electroactive isolates (Lovley et al., 2011; Logan et al., 2019). Although other microbes, most notably Shewanella species, have been helpful for developing an understanding of key extracellular electron transfer mechanisms (Shi et al., 2016; Lovley and Holmes, 2022), there are no pure cultures that are as effective in Fe (III) oxide reduction, DIET, and current production as G. sulfurreducens and its close relative G. metallireducens.