Biology and biotechnology of microbial pilus nanowires
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ENVIRONMENTAL MICROBIOLOGY - REVIEW
Biology and biotechnology of microbial pilus nanowires Morgen M. Clark1 · Gemma Reguera1 Received: 16 July 2020 / Accepted: 8 September 2020 © Society for Industrial Microbiology and Biotechnology 2020
Abstract Type IV pili (T4P) are bacterial appendages used for cell adhesion and surface motility. In metal-reducing bacteria in the genus Geobacter, they have the unique property of being conductive and essential to wire cells to extracellular electron acceptors and other cells within biofilms. These electroactive bacteria use a conserved pathway for biological assembly and disassembly of a short and aromatic dense peptide subunit (pilin). The polymerization of the pilins clusters aromatic residues optimally for charge transport and exposes ligands for metal immobilization and reduction. The simple design yet unique functionalities of conductive T4P afford opportunities for the scaled-up production of recombinant pilins and their in vitro assembly into electronic biomaterials of biotechnological interest. This review summarizes current knowledge of conductive T4P biogenesis and functions critical to actualize applications in bioelectronics, bioremediation, and nanotechnology. Keywords Type IV pili · Geobacter · Bioremediation · Bioelectronics · Nanotechnology · Extracellular electron transfer
Introduction Type IV pili (T4P) are versatile protein appendages frequently used by bacteria and archaea to colonize and move on surfaces, exchange genetic material, and interact with other cells [6, 21]. The canonical T4P biogenesis machinery of bacteria consists of a complex yet relatively conserved protein apparatus [6, 27] that recognizes, processes and stores a structural peptide (the pilin) in the membrane until ready for polymerization [21]. The mature pilin peptides provide the building blocks for the assembly of the T4P fiber on a dedicated membrane-bound protein complex and, in the case of Gram-negative bacteria, for fiber secretion through an outer membrane pore [27]. A distinctive feature of the bacterial T4P apparatus is its ability to power rapid cycles of pilin polymerization and depolymerization so the pilus fibers can grow and retract from the cell [25]. This dynamic feature allows some bacteria to translocate on surfaces, capture extracellular DNA, form microcolonies and biofilms, and secrete proteins [8, 33]. In Geobacter bacteria, T4P
* Gemma Reguera [email protected] 1
Department of Microbiology and Molecular Genetics, Michigan State University, 567 Wilson Rd, Rm 6190, Biomedical and Physical Science Building, East Lansing, MI 48823, USA
dynamics are essential for extracellular electron transfer to soluble and insoluble metals, radionuclides, and other cells within biofilms [35, 36]. Despite high conservation in the T4P biogenesis apparatus, Geobacter are unlike any other known bacteria in their ability to assemble conductive fibers [30] and use them as nanowires to electronically connect the cell to extracellular electron acceptors [11, 38]. Being embedded in the
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