@article {3094, title = {Expressing the Geobacter metallireducens PilA in Geobacter sulfurreducens Yields Pili with Exceptional Conductivity.}, journal = {mBio}, volume = {8}, year = {2017}, month = {2017 Jan 17}, abstract = {

UNLABELLED: The electrically conductive pili (e-pili) of Geobacter sulfurreducens serve as a model for a novel strategy for long-range extracellular electron transfer. e-pili are also a new class of bioelectronic materials. However, the only other Geobacter pili previously studied, which were from G.~uraniireducens, were poorly conductive. In order to obtain more information on the range of pili conductivities in Geobacter species, the pili of G.~metallireducens were investigated. Heterologously expressing the PilA gene of G.~metallireducens in G.~sulfurreducens yielded a G.~sulfurreducens strain, designated strain MP, that produced abundant pili. Strain MP exhibited phenotypes consistent with the presence of e-pili, such as high rates of Fe(III) oxide reduction and high current densities on graphite anodes. Individual pili prepared at physiologically relevant pH~7 had conductivities of 277 {\textpm} 18.9 S/cm (mean {\textpm} standard deviation), which is 5,000-fold higher than the conductivity of G.~sulfurreducens pili at pH~7 and nearly 1 million-fold higher than the conductivity of G.~uraniireducens pili at the same pH. A potential explanation for the higher conductivity of the G.~metallireducens pili is their greater density of aromatic amino acids, which are known to be important components in electron transport along the length of the pilus. The G.~metallireducens pili represent the most highly conductive pili found to date and suggest strategies for designing synthetic pili with even higher conductivities.

IMPORTANCE: e-pili are a remarkable electrically conductive material that can be sustainably produced without harsh chemical processes from renewable feedstocks and that contain no toxic components in the final product. Thus, e-pili offer an unprecedented potential for developing novel materials, electronic devices, and sensors for diverse applications with a new "green" technology. Increasing e-pili conductivity will even further expand their potential applications. A proven strategy is to design synthetic e-pili that contain tryptophan, an aromatic amino acid not found in previously studied e-pili. The studies reported here demonstrate that a productive alternative approach is to search more broadly in the microbial world. Surprisingly, even though G.~metallireducens and G.~sulfurreducens are closely related, the conductivities of their e-pili differ by more than 3 orders of magnitude. The ability to produce e-pili with high conductivity without generating a genetically modified product enhances the attractiveness of this novel electronic material.

}, keywords = {Electric Conductivity, Electrodes, Electron Transport, Ferric Compounds, Fimbriae Proteins, Gene Expression, Geobacter, Oxidation-Reduction, Recombinant Proteins}, issn = {2150-7511}, doi = {10.1128/mBio.02203-16}, author = {Tan, Yang and Adhikari, Ramesh Y and Malvankar, Nikhil S and Ward, Joy E and Woodard, Trevor L and Nevin, Kelly P and Lovley, Derek R} } @article {3101, title = {Synthetic Biological Protein Nanowires with High Conductivity.}, journal = {Small}, volume = {12}, year = {2016}, month = {2016 Sep}, pages = {4481-5}, abstract = {

Genetic modification to add tryptophan to PilA, the monomer for the electrically conductive pili of Geobacter sulfurreducens, yields conductive protein filaments 2000-fold more conductive than the wild-type pili while cutting the diameter in half to 1.5 nm.

}, keywords = {Amino Acid Sequence, Electric Conductivity, Fimbriae, Bacterial, Geobacter, Nanowires, Proteins, Tryptophan}, issn = {1613-6829}, doi = {10.1002/smll.201601112}, author = {Tan, Yang and Adhikari, Ramesh Y and Malvankar, Nikhil S and Pi, Shuang and Ward, Joy E and Woodard, Trevor L and Nevin, Kelly P and Xia, Qiangfei and Tuominen, Mark T and Lovley, Derek R} }