@article {3079,
	title = {The Archaellum of Methanospirillum hungatei Is Electrically Conductive.},
	journal = {mBio},
	volume = {10},
	year = {2019},
	month = {2019 Apr 16},
	abstract = {<p>Microbially produced electrically conductive protein filaments are of interest because they can function as conduits for long-range biological electron transfer. They also show promise as sustainably produced electronic materials. Until now, microbially produced conductive protein filaments have been reported only for bacteria. We report here that the archaellum of  is electrically conductive. This is the first demonstration that electrically conductive protein filaments have evolved in  Furthermore, the structure of the  archaellum was previously determined (N. Poweleit, P. Ge, H. N. Nguyen, R. R. O. Loo, et al., Nat Microbiol 2:16222, 2016, https://doi.org/10.1038/nmicrobiol.2016.222). Thus, the archaellum of  is the first microbially produced electrically conductive protein filament for which a structure is known. We analyzed the previously published structure and identified a core of tightly packed phenylalanines that is one likely route for electron conductance. The availability of the  archaellum structure is expected to substantially advance mechanistic evaluation of long-range electron transport in microbially produced electrically conductive filaments and to aid in the design of "green" electronic materials that can be microbially produced with renewable feedstocks. Microbially produced electrically conductive protein filaments are a revolutionary, sustainably produced, electronic material with broad potential applications. The design of new protein nanowires based on the known  archaellum structure could be a major advance over the current empirical design of synthetic protein nanowires from electrically conductive bacterial pili. An understanding of the diversity of outer-surface protein structures capable of electron transfer is important for developing models for microbial electrical communication with other cells and minerals in natural anaerobic environments. Extracellular electron exchange is also essential in engineered environments such as bioelectrochemical devices and anaerobic digesters converting wastes to methane. The finding that the archaellum of  is electrically conductive suggests that some archaea might be able to make long-range electrical connections with their external environment.</p>},
	keywords = {Electric Conductivity, Electricity, Electron Transport, Flagella, Methanospirillum, Phenylalanine},
	issn = {2150-7511},
	doi = {10.1128/mBio.00579-19},
	author = {Walker, David J F and Martz, Eric and Holmes, Dawn E and Zhou, Zimu and Nonnenmann, Stephen S and Lovley, Derek R}
}
@article {3093,
	title = {Biofilm Formation by Clostridium ljungdahlii Is Induced by Sodium Chloride Stress: Experimental Evaluation and Transcriptome Analysis.},
	journal = {PLoS One},
	volume = {12},
	year = {2017},
	month = {2017},
	pages = {e0170406},
	abstract = {<p>The acetogen Clostridium ljungdahlii is capable of syngas fermentation and microbial electrosynthesis. Biofilm formation could benefit both these applications, but was not yet reported for C. ljungdahlii. Biofilm formation does not occur under standard growth conditions, but attachment or aggregation could be induced by different stresses. The strongest biofilm formation was observed with the addition of sodium chloride. After 3 days of incubation, the biomass volume attached to a plastic surface was 20 times higher with than without the addition of 200 mM NaCl to the medium. The addition of NaCl also resulted in biofilm formation on glass, graphite and glassy carbon, the latter two being often used electrode materials for microbial electrosynthesis. Biofilms were composed of extracellular proteins, polysaccharides, as well as DNA, while pilus-like appendages were observed with, but not without, the addition of NaCl. A transcriptome analysis comparing planktonic (no NaCl) and biofilm (NaCl addition) cells showed that C. ljungdahlii coped with the salt stress by the upregulation of the general stress response, Na+ export and osmoprotectant accumulation. A potential role for poly-N-acetylglucosamines and D-alanine in biofilm formation was found. Flagellar motility was downregulated, while putative type IV pili biosynthesis genes were not expressed. Moreover, the gene expression analysis suggested the involvement of the transcriptional regulators LexA, Spo0A and CcpA in stress response and biofilm formation. This study showed that NaCl addition might be a valuable strategy to induce biofilm formation by C. ljungdahlii, which can improve the efficacy of syngas fermentation and microbial electrosynthesis applications.</p>},
	keywords = {Biofilms, Biomass, Carbon, Clostridium, Culture Media, Culture Techniques, Fimbriae, Bacterial, Flagella, Gene Expression Profiling, Gene Expression Regulation, Bacterial, Glass, Graphite, Osmotic Pressure, RNA, Bacterial, RNA, Ribosomal, Sodium Chloride, Spores, Bacterial, Stress, Physiological},
	issn = {1932-6203},
	doi = {10.1371/journal.pone.0170406},
	author = {Philips, Jo and Rabaey, Korneel and Lovley, Derek R and Vargas, Madeline}
}
@article {492,
	title = {Fluorescent properties of c-type cytochromes reveal their potential role as an extracytoplasmic electron sink in Geobacter sulfurreducens.},
	journal = {Environ Microbiol},
	volume = {10},
	year = {2008},
	month = {2008 Feb},
	pages = {497-505},
	abstract = {A novel fluorescence technique for monitoring the redox status of c-type cytochromes in Geobacter sulfurreducens was developed in order to evaluate the capacity of these extracytoplasmic cytochromes to store electrons during periods in which an external electron acceptor is not available. When intact cells in which the cytochromes were in a reduced state were excited at a wavelength of 350 nm, they fluoresced with maxima at 402 and 437 nm. Oxidation of the cytochromes resulted in a loss of fluorescence. This method was much more sensitive than the traditional approach of detecting c-type cytochromes via visible light absorbance. Furthermore, fluorescence of reduced cytochromes in individual cells could be detected via fluorescence microscopy, and the cytochromes in a G. sulfurreducens biofilm, remotely excited with an optical fibre, could be detected at distances as far as 5 cm. Fluorescence analysis of cytochrome oxidation and reduction of the external electron acceptor, anthraquinone-2,6-disulfonate, suggested that the extracytoplasmic cytochromes of G. sulfurreducens could store approximately 10(7) electrons per cell. Independent analysis of the haem content of the cells determined from analysis of incorporation of (55)Fe into cytochromes provided a similar estimate of cytochrome electron-storage capacity. This electron-storage capacity could, in the absence of an external electron acceptor, permit continued electron transfer across the inner membrane sufficient to supply the maintenance energy requirements for G. sulfurreducens for up to 8 min or enough proton motive force to power flagella motors for G. sulfurreducens motility. The fluorescence approach described here provides a sensitive method for evaluating the redox status of Geobacter species in culture and/or its environments. Furthermore, these results suggest that the periplasmic and outer-membrane cytochromes of Geobacter species act as capacitors, allowing continued electron transport, and thus viability and motility, for Geobacter species as they move between heterogeneously dispersed Fe(III) oxides during growth in the subsurface.},
	keywords = {Anthraquinones, Cytochromes c, Electron Transport, Ferric Compounds, Flagella, Fluorescence, Geobacter, Microscopy, Fluorescence, Oxidation-Reduction},
	issn = {1462-2920},
	doi = {10.1111/j.1462-2920.2007.01470.x},
	author = {Esteve-N{\'u}{\~n}ez, Abraham and Sosnik, Julian and Visconti, Pablo and Lovley, Derek R}
}
@article {586,
	title = {Geobacter metallireducens accesses insoluble Fe(III) oxide by chemotaxis.},
	journal = {Nature},
	volume = {416},
	year = {2002},
	month = {2002 Apr 18},
	pages = {767-9},
	abstract = {Microorganisms that use insoluble Fe(III) oxide as an electron acceptor can have an important function in the carbon and nutrient cycles of aquatic sediments and in the bioremediation of organic and metal contaminants in groundwater. Although Fe(III) oxides are often abundant, Fe(III)-reducing microbes are faced with the problem of how to access effectively an electron acceptor that can not diffuse to the cell. Fe(III)-reducing microorganisms in the genus Shewanella have resolved this problem by releasing soluble quinones that can carry electrons from the cell surface to Fe(III) oxide that is at a distance from the cell. Here we report that another Fe(III)-reducer, Geobacter metallireducens, has an alternative strategy for accessing Fe(III) oxides. Geobacter metallireducens specifically expresses flagella and pili only when grown on insoluble Fe(III) or Mn(IV) oxide, and is chemotactic towards Fe(II) and Mn(II) under these conditions. These results suggest that G. metallireducens senses when soluble electron acceptors are depleted and then synthesizes the appropriate appendages to permit it to search for, and establish contact with, insoluble Fe(III) or Mn(IV) oxide. This approach to the use of an insoluble electron acceptor may explain why Geobacter species predominate over other Fe(III) oxide-reducing microorganisms in a wide variety of sedimentary environments.},
	keywords = {Bacterial Proteins, Chemotaxis, Deltaproteobacteria, DNA-Binding Proteins, Ferric Compounds, Ferrous Compounds, Fimbriae Proteins, Fimbriae, Bacterial, Flagella, Manganese Compounds, Movement, Oxidation-Reduction, Oxides, Solubility},
	issn = {0028-0836},
	doi = {10.1038/416767a},
	author = {Childers, Susan E and Ciufo, Stacy and Lovley, Derek R}
}
