@article {3051, title = {Direct microbial electron uptake as a mechanism for stainless steel corrosion in aerobic environments.}, journal = {Water Res}, volume = {219}, year = {2022}, month = {2022 Jul 01}, pages = {118553}, abstract = {

Shewanella oneidensis MR-1 is an attractive model microbe for elucidating the biofilm-metal interactions that contribute to the billions of dollars in corrosion damage to industrial applications each year. Multiple mechanisms for S. oneidensis-enhanced corrosion have been proposed, but none of these mechanisms have previously been rigorously investigated with methods that rule out alternative routes for electron transfer. We found that S. oneidensis grown under aerobic conditions formed thick biofilms (\~{}50~{\textmu}m) on stainless steel coupons, accelerating corrosion over sterile controls. H and flavins were ruled out as intermediary electron carriers because stainless steel did not reduce riboflavin and previous studies have demonstrated stainless does not generate H. Strain ∆mtrCBA, in which the genes for the most abundant porin-cytochrome conduit in S. oneidensis were deleted, corroded stainless steel substantially less than wild-type in aerobic cultures. Wild-type biofilms readily reduced nitrate with stainless steel as the sole electron donor under anaerobic conditions, but strain ∆mtrCBA did not. These results demonstrate that S. oneidensis can directly consume electrons from iron-containing metals and illustrate how direct metal-to-microbe electron transfer can be an important route for corrosion, even in aerobic environments.

}, keywords = {Biofilms, Corrosion, Electron Transport, Electrons, Metals, Oxidation-Reduction, Stainless Steel, Steel}, issn = {1879-2448}, doi = {10.1016/j.watres.2022.118553}, author = {Zhou, Enze and Li, Feng and Zhang, Dawei and Xu, Dake and Li, Zhong and Jia, Ru and Jin, Yuting and Song, Hao and Li, Huabing and Wang, Qiang and Wang, Jianjun and Li, Xiaogang and Gu, Tingyue and Homborg, Axel M and Mol, Johannes M C and Smith, Jessica A and Wang, Fuhui 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 = {

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.

}, 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} } @article {3060, title = {Microbial corrosion of metals: The corrosion microbiome.}, journal = {Adv Microb Physiol}, volume = {78}, year = {2021}, month = {2021}, pages = {317-390}, abstract = {

Microbially catalyzed corrosion of metals is a substantial economic concern. Aerobic microbes primarily enhance Fe oxidation through indirect mechanisms and their impact appears to be limited compared to anaerobic microbes. Several anaerobic mechanisms are known to accelerate Fe oxidation. Microbes can consume H abiotically generated from the oxidation of Fe. Microbial H removal makes continued Fe oxidation more thermodynamically favorable. Extracellular hydrogenases further accelerate Fe oxidation. Organic electron shuttles such as flavins, phenazines, and possibly humic substances may replace H as the electron carrier between Fe and cells. Direct Fe-to-microbe electron transfer is also possible. Which of these anaerobic mechanisms predominates in model pure culture isolates is typically poorly documented because of a lack of functional genetic studies. Microbial mechanisms for Fe oxidation may also apply to some other metals. An ultimate goal of microbial metal corrosion research is to develop molecular tools to diagnose the occurrence, mechanisms, and rates of metal corrosion to guide the implementation of the most effective mitigation strategies. A systems biology approach that includes innovative isolation and characterization methods, as well as functional genomic investigations, will be required in order to identify the diagnostic features to be gleaned from meta-omic analysis of corroding materials. A better understanding of microbial metal corrosion mechanisms is expected to lead to new corrosion mitigation strategies. The understanding of the corrosion microbiome is clearly in its infancy, but interdisciplinary electrochemical, microbiological, and molecular tools are available to make rapid progress in this field.

}, keywords = {Corrosion, Electron Transport, Metals, Microbiota, Oxidation-Reduction}, issn = {2162-5468}, doi = {10.1016/bs.ampbs.2021.01.002}, author = {Lekbach, Yassir and Liu, Tao and Li, Yingchao and Moradi, Masoumeh and Dou, Wenwen and Xu, Dake and Smith, Jessica A and Lovley, Derek R} } @article {3074, title = {A Membrane-Bound Cytochrome Enables To Conserve Energy from Extracellular Electron Transfer.}, journal = {mBio}, volume = {10}, year = {2019}, month = {2019 Aug 20}, abstract = {

Extracellular electron exchange in species and closely related plays an important role in the global carbon cycle and enhances the speed and stability of anaerobic digestion by facilitating efficient syntrophic interactions. Here, we grew with methanol provided as the electron donor and the humic analogue, anthraquione-2,6-disulfonate (AQDS), provided as the electron acceptor when methane production was inhibited with bromoethanesulfonate. AQDS was reduced with simultaneous methane production in the absence of bromoethanesulfonate. Transcriptomics revealed that expression of the gene for the transmembrane, multiheme, -type cytochrome MmcA was higher in AQDS-respiring cells than in cells performing methylotrophic methanogenesis. A strain in which the gene for MmcA was deleted failed to grow via AQDS reduction but grew with the conversion of methanol or acetate to methane, suggesting that MmcA has a specialized role as a conduit for extracellular electron transfer. Enhanced expression of genes for methanol conversion to methyl-coenzyme M and the Rnf complex suggested that methanol is oxidized to carbon dioxide in AQDS-respiring cells through a pathway that is similar to methyl-coenzyme M oxidation in methanogenic cells. However, during AQDS respiration the Rnf complex and reduced methanophenazine probably transfer electrons to MmcA, which functions as the terminal reductase for AQDS reduction. Extracellular electron transfer may enable the survival of methanogens in dynamic environments in which oxidized humic substances and Fe(III) oxides are intermittently available. The availability of tools for genetic manipulation of makes it an excellent model microbe for evaluating -type cytochrome-dependent extracellular electron transfer in The discovery of a methanogen that can conserve energy to support growth solely from the oxidation of organic carbon coupled to the reduction of an extracellular electron acceptor expands the possible environments in which methanogens might thrive. The potential importance of -type cytochromes for extracellular electron transfer to syntrophic bacterial partners and/or Fe(III) minerals in some was previously proposed, but these studies with provide the first genetic evidence for cytochrome-based extracellular electron transfer in The results suggest parallels with Gram-negative bacteria, such as and species, in which multiheme outer-surface -type cytochromes are an essential component for electrical communication with the extracellular environment. offers an unprecedented opportunity to study mechanisms for energy conservation from the anaerobic oxidation of one-carbon organic compounds coupled to extracellular electron transfer in with implications not only for methanogens but possibly also for that anaerobically oxidize methane.

}, keywords = {Acetates, Anthraquinones, Cytochromes, Electron Transport, Electrons, Ferric Compounds, Gene Expression Regulation, Archaeal, Gram-Negative Bacteria, Membranes, Mesna, Methane, Methanol, Methanosarcina, Oxidation-Reduction, Oxidoreductases, Transcriptome}, issn = {2150-7511}, doi = {10.1128/mBio.00789-19}, author = {Holmes, Dawn E and Ueki, Toshiyuki and Tang, Hai-Yan and Zhou, Jinjie and Smith, Jessica A and Chaput, Gina and Lovley, Derek R} } @article {3136, title = {Anaerobic benzene oxidation via phenol in Geobacter metallireducens.}, journal = {Appl Environ Microbiol}, volume = {79}, year = {2013}, month = {2013 Dec}, pages = {7800-6}, abstract = {

Anaerobic activation of benzene is expected to represent a novel biochemistry of environmental significance. Therefore, benzene metabolism was investigated in Geobacter metallireducens, the only genetically tractable organism known to anaerobically degrade benzene. Trace amounts (<0.5 μM) of phenol accumulated in cultures of Geobacter metallireducens anaerobically oxidizing benzene to carbon dioxide with the reduction of Fe(III). Phenol was not detected in cell-free controls or in Fe(II)- and benzene-containing cultures of Geobacter sulfurreducens, a Geobacter species that cannot metabolize benzene. The phenol produced in G. metallireducens cultures was labeled with (18)O during growth in H2(18)O, as expected for anaerobic conversion of benzene to phenol. Analysis of whole-genome gene expression patterns indicated that genes for phenol metabolism were upregulated during growth on benzene but that genes for benzoate or toluene metabolism were not, further suggesting that phenol was an intermediate in benzene metabolism. Deletion of the genes for PpsA or PpcB, subunits of two enzymes specifically required for the metabolism of phenol, removed the capacity for benzene metabolism. These results demonstrate that benzene hydroxylation to phenol is an alternative to carboxylation for anaerobic benzene activation and suggest that this may be an important metabolic route for benzene removal in petroleum-contaminated groundwaters, in which Geobacter species are considered to play an important role in anaerobic benzene degradation.

}, keywords = {Anaerobiosis, Benzene, Carbon Dioxide, Gene Deletion, Gene Expression Profiling, Geobacter, Iron, Metabolic Networks and Pathways, Oxidation-Reduction, Phenol, Water}, issn = {1098-5336}, doi = {10.1128/AEM.03134-13}, author = {Zhang, Tian and Tremblay, Pier-Luc and Chaurasia, Akhilesh Kumar and Smith, Jessica A and Bain, Timothy S and Lovley, Derek R} } @article {3151, title = {Outer cell surface components essential for Fe(III) oxide reduction by Geobacter metallireducens.}, journal = {Appl Environ Microbiol}, volume = {79}, year = {2013}, month = {2013 Feb}, pages = {901-7}, abstract = {

Geobacter species are important Fe(III) reducers in a diversity of soils and sediments. Mechanisms for Fe(III) oxide reduction have been studied in detail in Geobacter sulfurreducens, but a number of the most thoroughly studied outer surface components of G. sulfurreducens, particularly c-type cytochromes, are not well conserved among Geobacter species. In order to identify cellular components potentially important for Fe(III) oxide reduction in Geobacter metallireducens, gene transcript abundance was compared in cells grown on Fe(III) oxide or soluble Fe(III) citrate with whole-genome microarrays. Outer-surface cytochromes were also identified. Deletion of genes for c-type cytochromes that had higher transcript abundance during growth on Fe(III) oxides and/or were detected in the outer-surface protein fraction identified six c-type cytochrome genes, that when deleted removed the capacity for Fe(III) oxide reduction. Several of the c-type cytochromes which were essential for Fe(III) oxide reduction in G. metallireducens have homologs in G. sulfurreducens that are not important for Fe(III) oxide reduction. Other genes essential for Fe(III) oxide reduction included a gene predicted to encode an NHL (Ncl-1-HT2A-Lin-41) repeat-containing protein and a gene potentially involved in pili glycosylation. Genes associated with flagellum-based motility, chemotaxis, and pili had higher transcript abundance during growth on Fe(III) oxide, consistent with the previously proposed importance of these components in Fe(III) oxide reduction. These results demonstrate that there are similarities in extracellular electron transfer between G. metallireducens and G. sulfurreducens but the outer-surface c-type cytochromes involved in Fe(III) oxide reduction are different.

}, keywords = {Bacterial Proteins, Culture Media, Cytochromes c, Electron Transport, Ferric Compounds, Gene Deletion, Gene Expression Profiling, Geobacter, Microarray Analysis, Oxidation-Reduction}, issn = {1098-5336}, doi = {10.1128/AEM.02954-12}, author = {Smith, Jessica A and Lovley, Derek R and Tremblay, Pier-Luc} } @article {421, title = {Anaerobic oxidation of benzene by the hyperthermophilic archaeon Ferroglobus placidus.}, journal = {Appl Environ Microbiol}, volume = {77}, year = {2011}, month = {2011 Sep}, pages = {5926-33}, abstract = {Anaerobic benzene oxidation coupled to the reduction of Fe(III) was studied in Ferroglobus placidus in order to learn more about how such a stable molecule could be metabolized under strict anaerobic conditions. F. placidus conserved energy to support growth at 85{\textdegree}C in a medium with benzene provided as the sole electron donor and Fe(III) as the sole electron acceptor. The stoichiometry of benzene loss and Fe(III) reduction, as well as the conversion of [(14)C]benzene to [(14)C]carbon dioxide, was consistent with complete oxidation of benzene to carbon dioxide with electron transfer to Fe(III). Benzoate, but not phenol or toluene, accumulated at low levels during benzene metabolism, and [(14)C]benzoate was produced from [(14)C]benzene. Analysis of gene transcript levels revealed increased expression of genes encoding enzymes for anaerobic benzoate degradation during growth on benzene versus growth on acetate, but genes involved in phenol degradation were not upregulated during growth on benzene. A gene for a putative carboxylase that was more highly expressed in benzene- than in benzoate-grown cells was identified. These results suggest that benzene is carboxylated to benzoate and that phenol is not an important intermediate in the benzene metabolism of F. placidus. This is the first demonstration of a microorganism in pure culture that can grow on benzene under strict anaerobic conditions and for which there is strong evidence for degradation of benzene via clearly defined anaerobic metabolic pathways. Thus, F. placidus provides a much-needed pure culture model for further studies on the anaerobic activation of benzene in microorganisms.}, keywords = {Anaerobiosis, Archaeoglobales, Benzene, Carbon Radioisotopes, Ferric Compounds, Gene Expression Profiling, Hot Temperature, Isotope Labeling, Oxidation-Reduction}, issn = {1098-5336}, doi = {10.1128/AEM.05452-11}, author = {Holmes, Dawn E and Risso, Carla and Smith, Jessica A and Lovley, Derek R} }