@article {3097, title = {Happy together: microbial communities that hook up to swap electrons.}, journal = {ISME J}, volume = {11}, year = {2017}, month = {2017 Feb}, pages = {327-336}, abstract = {

The discovery of direct interspecies electron transfer (DIET) and cable bacteria has demonstrated that microbial cells can exchange electrons over long distances (μm-cm) through electrical connections. For example, in the presence of cable bacteria electrons are rapidly transported over centimeter distances, coupling the oxidation of reduced sulfur compounds in anoxic sediments to oxygen reduction in overlying surficial sediments. Bacteria and archaea wired for DIET are found in anaerobic methane-producing and methane-consuming communities. Electrical connections between gut microbes and host cells have also been proposed. Iterative environmental and defined culture studies on methanogenic communities revealed the importance of electrically conductive pili and c-type cytochromes in natural electrical grids, and demonstrated that conductive carbon materials and magnetite can substitute for these biological connectors to facilitate DIET. This understanding has led to strategies to enhance and stabilize anaerobic digestion. Key unknowns warranting further investigation include elucidation of the archaeal electrical connections facilitating DIET-based methane production and consumption; and the mechanisms for long-range electron transfer through cable bacteria. A better understanding of mechanisms for cell-to-cell electron transfer could facilitate the hunt for additional electrically connected microbial communities with omics approaches and could advance spin-off applications such as the development of sustainable bioelectronics materials and bioelectrochemical technologies.

}, keywords = {Archaea, Bacteria, Electron Transport, Methane, Microbial Consortia, Microbial Interactions, Models, Biological, Oxidation-Reduction}, issn = {1751-7370}, doi = {10.1038/ismej.2016.136}, author = {Lovley, Derek R} } @article {3104, title = {Potential enhancement of direct interspecies electron transfer for syntrophic metabolism of propionate and butyrate with biochar in up-flow anaerobic sludge blanket reactors.}, journal = {Bioresour Technol}, volume = {209}, year = {2016}, month = {2016 Jun}, pages = {148-56}, abstract = {

Promoting direct interspecies electron transfer (DIET) to enhance syntrophic metabolism may be a strategy for accelerating the conversion of organic wastes to methane, but microorganisms capable of metabolizing propionate and butyrate via DIET under methanogenic conditions have yet to be identified. In an attempt to establish methanogenic communities metabolizing propionate or butyrate with DIET, enrichments were initiated with up-flow anaerobic sludge blanket (UASB), similar to those that were previously reported to support communities that metabolized ethanol with DIET that relied on direct biological electrical connections. In the absence of any amendments, microbial communities enriched were dominated by microorganisms closely related to pure cultures that are known to metabolize propionate or butyrate to acetate with production of H2. When biochar was added to the reactors there was a substantial enrichment on the biochar surface of 16S rRNA gene sequences closely related to Geobacter and Methanosaeta species known to participate in DIET.

}, keywords = {Acetates, Bioreactors, Butyric Acid, Charcoal, Electron Transport, Geobacter, Methane, Microbial Consortia, Propionates, RNA, Ribosomal, 16S, Sewage, Waste Disposal, Fluid}, issn = {1873-2976}, doi = {10.1016/j.biortech.2016.03.005}, author = {Zhao, Zhiqiang and Zhang, Yaobin and Holmes, Dawn E and Dang, Yan and Woodard, Trevor L and Nevin, Kelly P and Lovley, Derek R} } @article {3117, title = {Carbon cloth stimulates direct interspecies electron transfer in syntrophic co-cultures.}, journal = {Bioresour Technol}, volume = {173}, year = {2014}, month = {2014 Dec}, pages = {82-86}, abstract = {

This study investigated the possibility that the electrical conductivity of carbon cloth accelerates direct interspecies electron transfer (DIET) in co-cultures. Carbon cloth accelerated metabolism of DIET co-cultures (Geobacter metallireducens-Geobacter sulfurreducens and G.metallireducens-Methanosarcina barkeri) but did not promote metabolism of co-cultures performing interspecies H2 transfer (Desulfovibrio vulgaris-G.sulfurreducens). On the other hand, DIET co-cultures were not stimulated by poorly conductive cotton cloth. Mutant strains lacking electrically conductive pili, or pili-associated cytochromes participated in DIET only in the presence of carbon cloth. In co-cultures promoted by carbon cloth, cells were primarily associated with the cloth although the syntrophic partners were too far apart for cell-to-cell biological electrical connections to be feasible. Carbon cloth seemingly mediated interspecies electron transfer between the distant syntrophic partners. These results suggest that the ability of carbon cloth to accelerate DIET should be considered in anaerobic digester designs that incorporate carbon cloth.

}, keywords = {Carbon, Cell Communication, Coculture Techniques, Electric Conductivity, Electron Transport, Geobacter, Materials Testing, Membranes, Artificial, Microbial Consortia, Oxidation-Reduction, Symbiosis}, issn = {1873-2976}, doi = {10.1016/j.biortech.2014.09.009}, author = {Chen, Shanshan and Rotaru, Amelia-Elena and Liu, Fanghua and Philips, Jo and Woodard, Trevor L and Nevin, Kelly P and Lovley, Derek R} } @article {3138, title = {Field evidence of selenium bioreduction in a uranium-contaminated aquifer.}, journal = {Environ Microbiol Rep}, volume = {5}, year = {2013}, month = {2013 Jun}, pages = {444-52}, abstract = {

Removal of selenium from groundwater was documented during injection of acetate into a uranium-contaminated aquifer near Rifle, Colorado (USA). Bioreduction of aqueous selenium to its elemental form (Se0) concentrated it within mineralized biofilms affixed to tubing used to circulate acetate-amended groundwater. Scanning and transmission electron microscopy revealed close association between Se0 precipitates and cell surfaces, with Se0 aggregates having a diameter of 50-60 nm. Accumulation of Se0 within biofilms occurred over a three-week interval at a rate of c. 9 mg Se0 m(-2) tubing day(-1). Removal was inferred to result from the activity of a mixed microbial community within the biofilms capable of coupling acetate oxidation to the reduction of oxygen, nitrate and selenate. Phylogenetic analysis of the biofilm revealed a community dominated by strains of Dechloromonas sp. and Thauera sp., with isolates exhibiting genetic similarity to the latter known to reduce selenate to Se0. Enrichment cultures of selenate-respiring microorganisms were readily established using Rifle site groundwater and acetate, with cultures dominated by strains closely related to D. aromatica (96-99\% similarity). Predominance of Dechloromonas sp. in recovered biofilms and enrichments suggests this microorganism may play a role in the removal of selenium oxyanions present in Se-impacted groundwaters and sediments.

}, keywords = {Acetates, Betaproteobacteria, Biodegradation, Environmental, Biofilms, Colorado, Groundwater, Humans, Microbial Consortia, Oxidation-Reduction, Oxygen, Phylogeny, RNA, Ribosomal, 16S, Selenic Acid, Selenium, Selenium Compounds, Thauera, Uranium, Water Pollutants, Chemical}, issn = {1758-2229}, doi = {10.1111/1758-2229.12032}, author = {Williams, Kenneth H and Wilkins, Michael J and N{\textquoteright}Guessan, A Lucie and Arey, Bruce and Dodova, Elena and Dohnalkova, Alice and Holmes, Dawn and Lovley, Derek R and Long, Philip E} } @article {368, title = {Anaerobic decomposition of switchgrass by tropical soil-derived feedstock-adapted consortia.}, journal = {MBio}, volume = {3}, year = {2012}, month = {2012}, abstract = {Tropical forest soils decompose litter rapidly with frequent episodes of anoxic conditions, making it likely that bacteria using alternate terminal electron acceptors (TEAs) play a large role in decomposition. This makes these soils useful templates for improving biofuel production. To investigate how TEAs affect decomposition, we cultivated feedstock-adapted consortia (FACs) derived from two tropical forest soils collected from the ends of a rainfall gradient: organic matter-rich tropical cloud forest (CF) soils, which experience sustained low redox, and iron-rich tropical rain forest (RF) soils, which experience rapidly fluctuating redox. Communities were anaerobically passed through three transfers of 10 weeks each with switchgrass as a sole carbon (C) source; FACs were then amended with nitrate, sulfate, or iron oxide. C mineralization and cellulase activities were higher in CF-FACs than in RF-FACs. Pyrosequencing of the small-subunit rRNA revealed members of the Firmicutes, Bacteroidetes, and Alphaproteobacteria as dominant. RF- and CF-FAC communities were not different in microbial diversity or biomass. The RF-FACs, derived from fluctuating redox soils, were the most responsive to the addition of TEAs, while the CF-FACs were overall more efficient and productive, both on a per-gram switchgrass and a per-cell biomass basis. These results suggest that decomposing microbial communities in fluctuating redox environments are adapted to the presence of a diversity of TEAs and ready to take advantage of them. More importantly, these data highlight the role of local environmental conditions in shaping microbial community function that may be separate from phylogenetic structure. IMPORTANCE: After multiple transfers, we established microbial consortia derived from two tropical forest soils with different native redox conditions. Communities derived from the rapidly fluctuating redox environment maintained a capacity to use added terminal electron acceptors (TEAs) after multiple transfers, though they were not present during the enrichment. Communities derived from lower-redox soils were not responsive to TEA addition but were much more efficient at switchgrass decomposition. Though the communities were different, diversity was not, and both were dominated by many of the same species of clostridia. This reflects the inadequacy of rRNA for determining the function of microbial communities, in this case the retained ability to utilize TEAs that were not part of the selective growth conditions. More importantly, this suggests that microbial community function is shaped by life history, where environmental factors produce heritable traits through natural selection over time, creating variation in the community, a phenomenon not well documented for microbes.}, keywords = {Adaptation, Physiological, Alphaproteobacteria, Anaerobiosis, Bacteroidetes, Biota, Biotransformation, Carbon, Electron Transport, Enzyme Activation, Ferric Compounds, Genes, rRNA, Microbial Consortia, Nitrates, Oxidation-Reduction, Panicum, Phylogeny, Rain, Soil Microbiology, Sulfates, Trees, Tropical Climate}, issn = {2150-7511}, doi = {10.1128/mBio.00249-11}, author = {Deangelis, Kristen M and Fortney, Julian L and Borglin, Sharon and Silver, Whendee L and Simmons, Blake A and Hazen, Terry C} } @article {406, title = {Electrical conductivity in a mixed-species biofilm.}, journal = {Appl Environ Microbiol}, volume = {78}, year = {2012}, month = {2012 Aug}, pages = {5967-71}, abstract = {

Geobacter sulfurreducens can form electrically conductive biofilms, but the potential for conductivity through mixed-species biofilms has not been examined. A current-producing biofilm grown from a wastewater sludge inoculum was highly conductive with low charge transfer resistance even though microorganisms other than Geobacteraceae accounted for nearly half the microbial community.

}, keywords = {Biofilms, Electric Conductivity, Microbial Consortia, Sewage}, issn = {1098-5336}, doi = {10.1128/AEM.01803-12}, author = {Malvankar, Nikhil S and Lau, Joanne and Nevin, Kelly P and Franks, Ashley E and Tuominen, Mark T and Lovley, Derek R} } @article {728, title = {Performance of a pilot-scale packed bed reactor for perchlorate reduction using a sulfur oxidizing bacterial consortium.}, journal = {Biotechnol Bioeng}, volume = {109}, year = {2012}, month = {2012 Mar}, pages = {637-46}, abstract = {A novel sulfur-utilizing perchlorate reducing bacterial consortium successfully treated perchlorate (ClO$_{4}$$^{-}$) in prior batch and bench-scale packed bed reactor (PBR) studies. This study examined the scale up of this process for treatment of water from a ClO $_{4}$$^{-}$ and RDX contaminated aquifer in Cape Cod Massachusetts. A pilot-scale upflow PBR (\~{}250-L) was constructed with elemental sulfur and crushed oyster shell packing media. The reactor was inoculated with sulfur oxidizing ClO$_{4}$$^{-}$ reducing cultures enriched from a wastewater seed. Sodium sulfite provided a good method of dissolved oxygen removal in batch cultures, but was found to promote the growth of bacteria that carry out sulfur disproportionation and sulfate reduction, which inhibited ClO$_{4}$$^{-}$ reduction in the pilot system. After terminating sulfite addition, the PBR successfully removed 96\% of the influent ClO$_{4}$$^{-}$ in the groundwater at an empty bed contact time (EBCT) of 12 h (effluent ClO$_{4}$$^{-}$ of 4.2 {\textmu}g L(-1)). Simultaneous ClO$_{4}$$^{-}$ and NO$_{3}$$^{-}$ reduction was observed in the lower half of the reactor before reactions shifted to sulfur disproportionation and sulfate reduction. Analyses of water quality profiles were supported by molecular analysis, which showed distinct groupings of ClO$_{4}$$^{-}$ and NO$_{3}$$^{-}$ degrading organisms at the inlet of the PBR, while sulfur disproportionation was the primary biological process occurring in the top potion of the reactor.}, keywords = {Bioreactors, Cluster Analysis, DNA, Bacterial, DNA, Ribosomal, Massachusetts, Microbial Consortia, Molecular Sequence Data, Oxidation-Reduction, Perchloric Acid, Phylogeny, RNA, Ribosomal, 16S, Sequence Analysis, DNA, Sulfites, Sulfur, Water Microbiology, Water Pollutants, Chemical, Water Purification}, issn = {1097-0290}, doi = {10.1002/bit.24354}, author = {Boles, Amber R and Conneely, Teresa and McKeever, Robert and Nixon, Paul and N{\"u}sslein, Klaus R and Ergas, Sarina J} } @article {431, title = {Direct exchange of electrons within aggregates of an evolved syntrophic coculture of anaerobic bacteria.}, journal = {Science}, volume = {330}, year = {2010}, month = {2010 Dec 3}, pages = {1413-5}, abstract = {Microbial consortia that cooperatively exchange electrons play a key role in the anaerobic processing of organic matter. Interspecies hydrogen transfer is a well-documented strategy for electron exchange in dispersed laboratory cultures, but cooperative partners in natural environments often form multispecies aggregates. We found that laboratory evolution of a coculture of Geobacter metallireducens and Geobacter sulfurreducens metabolizing ethanol favored the formation of aggregates that were electrically conductive. Sequencing aggregate DNA revealed selection for a mutation that enhances the production of a c-type cytochrome involved in extracellular electron transfer and accelerates the formation of aggregates. Aggregate formation was also much faster in mutants that were deficient in interspecies hydrogen transfer, further suggesting direct interspecies electron transfer.}, keywords = {Anaerobiosis, Bacterial Proteins, Biological Evolution, Culture Media, Cytochrome c Group, Electron Transport, Electrons, Ethanol, Fimbriae Proteins, Geobacter, Hydrogen, Microbial Consortia, Microbial Interactions, Mutation, Oxidation-Reduction, Selection, Genetic}, issn = {1095-9203}, doi = {10.1126/science.1196526}, author = {Summers, Zarath M and Fogarty, Heather E and Leang, Ching and Franks, Ashley E and Malvankar, Nikhil S and Lovley, Derek R} }