@article {3068, title = {Protein Nanowires: the Electrification of the Microbial World and Maybe Our Own.}, journal = {J Bacteriol}, volume = {202}, year = {2020}, month = {2020 Sep 23}, abstract = {

Electrically conductive protein nanowires appear to be widespread in the microbial world and are a revolutionary "green" material for the fabrication of electronic devices. Electrically conductive pili (e-pili) assembled from type IV pilin monomers have independently evolved multiple times in microbial history as have electrically conductive archaella (e-archaella) assembled from homologous archaellin monomers. A role for e-pili in long-range (micrometer) extracellular electron transport has been demonstrated in some microbes. The surprising finding of e-pili in syntrophic bacteria and the role of e-pili as conduits for direct interspecies electron transfer have necessitated a reassessment of routes for electron flux in important methanogenic environments, such as anaerobic digesters and terrestrial wetlands. Pilin monomers similar to those found in e-pili may also be a major building block of the conductive "cables" that transport electrons over centimeter distances through continuous filaments of cable bacteria consisting of a thousand cells or more. Protein nanowires harvested from microbes have many functional and sustainability advantages over traditional nanowire materials and have already yielded novel electronic devices for sustainable electricity production, neuromorphic memory, and sensing. e-pili can be mass produced with an chassis, providing a ready source of material for electronics as well as for studies on the basic mechanisms for long-range electron transport along protein nanowires. Continued exploration is required to better understand the electrification of microbial communities with microbial nanowires and to expand the "green toolbox" of sustainable materials for wiring and powering the emerging "Internet of things."

}, keywords = {Electric Conductivity, Electron Transport, Fimbriae Proteins, Fimbriae, Bacterial, Geobacter, Microscopy, Electron, Nanowires, Protein Engineering}, issn = {1098-5530}, doi = {10.1128/JB.00331-20}, author = {Lovley, Derek R and Holmes, Dawn E} } @article {3072, title = {Syntrophus conductive pili demonstrate that common hydrogen-donating syntrophs can have a direct electron transfer option.}, journal = {ISME J}, volume = {14}, year = {2020}, month = {2020 Mar}, pages = {837-846}, abstract = {

Syntrophic interspecies electron exchange is essential for the stable functioning of diverse anaerobic microbial communities. Hydrogen/formate interspecies electron transfer (HFIT), in which H and/or formate function as diffusible electron carriers, has been considered to be the primary mechanism for electron transfer because most common syntrophs were thought to lack biochemical components, such as electrically conductive pili (e-pili), necessary for direct interspecies electron transfer (DIET). Here we report that Syntrophus aciditrophicus, one of the most intensively studied microbial models for HFIT, produces e-pili and can grow via DIET. Heterologous expression of the putative S. aciditrophicus type IV pilin gene in Geobacter sulfurreducens yielded conductive pili of the same diameter (4 nm) and conductance of the native S. aciditrophicus pili and enabled long-range electron transport in G. sulfurreducens. S. aciditrophicus lacked abundant c-type cytochromes often associated with DIET. Pilin genes likely to yield e-pili were found in other genera of hydrogen/formate-producing syntrophs. The finding that DIET is a likely option for diverse syntrophs that are abundant in many anaerobic environments necessitates a reexamination of the paradigm that HFIT is the predominant mechanism for syntrophic electron exchange within anaerobic microbial communities of biogeochemical and practical significance.

}, keywords = {Deltaproteobacteria, Electric Conductivity, Electron Transport, Electrons, Fimbriae Proteins, Fimbriae, Bacterial, Formates, Geobacter, Hydrogen}, issn = {1751-7370}, doi = {10.1038/s41396-019-0575-9}, author = {Walker, David J F and Nevin, Kelly P and Holmes, Dawn E and Rotaru, Amelia-Elena and Ward, Joy E and Woodard, Trevor L and Zhu, Jiaxin and Ueki, Toshiyuki and Nonnenmann, Stephen S and McInerney, Michael J and Lovley, Derek R} } @article {3087, title = {Electrically conductive pili from pilin genes of phylogenetically diverse microorganisms.}, journal = {ISME J}, volume = {12}, year = {2018}, month = {2018 Jan}, pages = {48-58}, abstract = {

The possibility that bacteria other than Geobacter species might contain genes for electrically conductive pili (e-pili) was investigated by heterologously expressing pilin genes of interest in Geobacter sulfurreducens. Strains of G. sulfurreducens producing high current densities, which are only possible with e-pili, were obtained with pilin genes from Flexistipes sinusarabici, Calditerrivibrio nitroreducens and Desulfurivibrio alkaliphilus. The conductance of pili from these strains was comparable to native G. sulfurreducens e-pili. The e-pili derived from C. nitroreducens, and D. alkaliphilus pilin genes are the first examples of relatively long (>100 amino acids) pilin monomers assembling into e-pili. The pilin gene from Candidatus Desulfofervidus auxilii did not yield e-pili, suggesting that the hypothesis that this sulfate reducer wires itself with e-pili to methane-oxidizing archaea to enable anaerobic methane oxidation should be reevaluated. A high density of aromatic amino acids and a lack of substantial aromatic-free gaps along the length of long pilins may be important characteristics leading to e-pili. This study demonstrates a simple method to screen pilin genes from difficult-to-culture microorganisms for their potential to yield e-pili; reveals new sources for biologically based electronic materials; and suggests that a wide phylogenetic diversity of microorganisms may use e-pili for extracellular electron exchange.

}, keywords = {Deltaproteobacteria, Electric Conductivity, Fimbriae Proteins, Fimbriae, Bacterial, Methane, Oxidation-Reduction, Phylogeny}, issn = {1751-7370}, doi = {10.1038/ismej.2017.141}, author = {Walker, David Jf and Adhikari, Ramesh Y and Holmes, Dawn E and Ward, Joy E and Woodard, Trevor L and Nevin, Kelly P and Lovley, Derek R} } @article {3091, title = {The electrically conductive pili of pecies are a recently evolved feature for extracellular electron transfer.}, journal = {Microb Genom}, volume = {2}, year = {2016}, month = {2016 Aug}, pages = {e000072}, abstract = {

The electrically conductive pili (e-pili) of have environmental and practical significance because they can facilitate electron transfer to insoluble Fe(III) oxides; to other microbial species; and through electrically conductive biofilms. E-pili conductivity has been attributed to the truncated PilA monomer, which permits tight packing of aromatic amino acids to form a conductive path along the length of e-pili. In order to better understand the evolution and distribution of e-pili in the microbial world, type IVa PilA proteins from various Gram-negative and Gram-positive bacteria were examined with a particular emphasis on Fe(III)-respiring bacteria. E-pilin genes are primarily restricted to a tight phylogenetic group in the order Desulfuromonadales. The downstream gene in all but one of the Desulfuromonadales that possess an e-pilin gene is a gene previously annotated as {\textquoteright}{\textquoteright} that has characteristics suggesting that it may encode an outer-membrane protein. Other genes associated with pilin function are clustered with e-pilin and {\textquoteright}{\textquoteright} genes in the Desulfuromonadales. In contrast, in the few bacteria outside the Desulfuromonadales that contain e-pilin genes, the other genes required for pilin function may have been acquired through horizontal gene transfer. Of the 95 known Fe(III)-reducing micro-organisms for which genomes are available, 80 \% lack e-pilin genes, suggesting that e-pili are just one of several mechanisms involved in extracellular electron transport. These studies provide insight into where and when e-pili are likely to contribute to extracellular electron transport processes that are biogeochemically important and involved in bioenergy conversions.

}, keywords = {Electromagnetic Phenomena, Electron Transport, Ferric Compounds, Fimbriae Proteins, Fimbriae, Bacterial, Geobacter, Phylogeny}, issn = {2057-5858}, doi = {10.1099/mgen.0.000072}, author = {Holmes, Dawn E and Dang, Yan and Walker, David J F and Lovley, Derek R} }