@article {3058,
	title = {Direct Observation of Electrically Conductive Pili Emanating from .},
	journal = {mBio},
	volume = {12},
	year = {2021},
	month = {2021 Aug 31},
	pages = {e0220921},
	abstract = {<p>Geobacter sulfurreducens is a model microbe for elucidating the mechanisms for extracellular electron transfer in several biogeochemical cycles, bioelectrochemical applications, and microbial metal corrosion. Multiple lines of evidence previously suggested that electrically conductive pili (e-pili) are an essential conduit for long-range extracellular electron transport in G. sulfurreducens. However, it has recently been reported that G. sulfurreducens does not express e-pili and that filaments comprised of multi-heme -type cytochromes are responsible for long-range electron transport. This possibility was directly investigated by examining cells, rather than filament preparations, with atomic force microscopy. Approximately 90\% of the filaments emanating from wild-type cells had a diameter (3 nm) and conductance consistent with previous reports of e-pili harvested from G. sulfurreducens or heterologously expressed in Escherichia coli from the G. sulfurreducens pilin gene. The remaining 10\% of filaments had a morphology consistent with filaments comprised of the -type cytochrome OmcS. A strain expressing a modified pilin gene designed to yield poorly conductive pili expressed 90\% filaments with a 3-nm diameter, but greatly reduced conductance, further indicating that the 3-nm diameter conductive filaments in the wild-type strain were e-pili. A strain in which genes for five of the most abundant outer-surface -type cytochromes, including OmcS, were deleted yielded only 3-nm-diameter filaments with the same conductance as in the wild type. These results demonstrate that e-pili are the most abundant conductive filaments expressed by G. sulfurreducens, consistent with previous functional studies demonstrating the need for e-pili for long-range extracellular electron transfer.  Electroactive microbes have significant environmental impacts, as well as applications in bioenergy and bioremediation. The composition, function, and even existence of electrically conductive pili (e-pili) has been one of the most contentious areas of investigation in electromicrobiology, in part because e-pili offer a mechanism for long-range electron transport that does not involve the metal cofactors common in much of biological electron transport. This study demonstrates that e-pili are abundant filaments emanating from Geobacter sulfurreducens, which serves as a model for long-range extracellular electron transfer in direct interspecies electron transfer, dissimilatory metal reduction, microbe-electrode exchange, and corrosion caused by direct electron uptake from Fe(0). The methods described in this study provide a simple strategy for evaluating the distribution of conductive filaments throughout the microbial world with an approach that avoids artifactual production and/or enrichment of filaments that may not be physiologically relevant.</p>},
	keywords = {Electric Conductivity, Electrons, Escherichia coli, Fimbriae Proteins, Fimbriae, Bacterial, Geobacter, Microscopy, Atomic Force, Oxidation-Reduction},
	issn = {2150-7511},
	doi = {10.1128/mBio.02209-21},
	author = {Liu, Xinying and Walker, David J F and Nonnenmann, Stephen S and Sun, Dezhi and Lovley, Derek R}
}
@article {3055,
	title = {Extracellular Electron Exchange Capabilities of  and .},
	journal = {Environ Sci Technol},
	volume = {55},
	year = {2021},
	month = {2021 Dec 07},
	pages = {16195-16203},
	abstract = {<p>Microbial extracellular electron transfer plays an important role in diverse biogeochemical cycles, metal corrosion, bioelectrochemical technologies, and anaerobic digestion. Evaluation of electron uptake from pure Fe(0) and stainless steel indicated that, in contrast to previous speculation in the literature,  and  are not able to directly extract electrons from solid-phase electron-donating surfaces.  grew with Fe(III) as the electron acceptor, but  did not.  reduced Fe(III) oxide occluded within porous alginate beads, suggesting that it released a soluble electron shuttle to promote Fe(III) oxide reduction. Conductive atomic force microscopy revealed that the  pili are electrically conductive and the expression of a gene encoding an aromatics-rich putative pilin was upregulated during growth on Fe(III) oxide. The expression of genes for multi-heme -type cytochromes was not upregulated during growth with Fe(III) as the electron acceptor, and genes for a porin-cytochrome conduit across the outer membrane were not apparent in the genome. The results suggest that  has adopted a novel combination of strategies to enable extracellular electron transport, which may be of biogeochemical and technological significance.</p>},
	keywords = {Desulfovibrio, Electron Transport, Electrons, Ferric Compounds, Geobacter, Oxidation-Reduction},
	issn = {1520-5851},
	doi = {10.1021/acs.est.1c04071},
	author = {Liang, Dandan and Liu, Xinying and Woodard, Trevor L and Holmes, Dawn E and Smith, Jessica A and Nevin, Kelly P and Feng, Yujie and Lovley, Derek R}
}
