Probing cytoplasmic peroxide metabolism in Shewanella oneidensis.

The facultative anaerobe Shewanella oneidensis respires an extensive set of electron acceptors and, as a consequence, can leak electrons to produce reactive oxygen species such as hydrogen peroxide (H2O2). However, the effects of respiration on cytoplasmic redox homeostasis are poorly characterized in comparison. In the present study, the H2O2 sensor HyPer-3 was deployed to interrogate cytoplasmic peroxide levels of both wild-type and gene deletion mutants lacking peroxide scavenging enzymes following exposure to H2O2.

Iodate Reduction by Requires Genes Encoding an Extracellular Dimethylsulfoxide Reductase.

Microbial iodate (IO ) reduction is a major component of the iodine biogeochemical reaction network in anaerobic marine basins and radioactive iodine-contaminated subsurface environments. Alternative iodine remediation technologies include microbial reduction of IO to iodide (I) and microbial methylation of I to volatile gases. The metal reduction pathway is required for anaerobic IO respiration by the gammaproteobacterium .

Resistance of perfluorooctanoic acid to degradation by the microbially driven Fenton reaction.

Per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) have received recent heightened attention as emerging contaminants. Due to widespread application in household products and aqueous film-forming foams, PFAS are globally distributed in the environment, and bioaccumulate in the blood and tissues of mammals including humans. The microbially driven Fenton reaction, a hybrid biotic/abiotic hydroxyl radical (HO•)-generating system, previously degraded a wide variety of persistant organic pollutants.

Novel insights into the taxonomic diversity and molecular mechanisms of bacterial Mn(III) reduction.

Soluble ligand-bound Mn(III) can support anaerobic microbial respiration in diverse aquatic environments. Thus far, Mn(III) reduction has only been associated with certain Gammaproteobacteria. Here, we characterized microbial communities enriched from Mn-replete sediments of Lake Matano, Indonesia.

Metal Reduction and Protein Secretion Genes Required for Iodate Reduction by Shewanella oneidensis.

The metal-reducing gammaproteobacterium reduces iodate (IO) as an anaerobic terminal electron acceptor. Microbial IO electron transport pathways are postulated to terminate with nitrate (NO) reductase, which reduces IO as an alternative electron acceptor. Recent studies with , however, have demonstrated that NO reductase is not involved in IO reduction.

Whole-genome sequencing reveals that Shewanella haliotis Kim et al. 2007 can be considered a later heterotypic synonym of Shewanella algae Simidu et al. 1990.

Previously, experimental DNA-DNA hybridization (DDH) between Shewanellahaliotis JCM 14758 and Shewanellaalgae JCM 21037 had suggested that the two strains could be considered different species, despite minimal phenotypic differences. The recent isolation of Shewanella sp. MN-01, with 99 % 16S rRNA gene identity to S.

Degradation of the recalcitrant oil spill components anthracene and pyrene by a microbially driven Fenton reaction.

Oil spill components include a range of toxic saturated, aromatic and polar hydrocarbons, including pyrene and anthracene. Such contaminants harm natural ecosystems, adversely affect human health and negatively impact tourism and the fishing industries. Current physical, chemical and biological remediation technologies are often unable to completely remove recalcitrant oil spill components, which accumulate at levels greater than regulatory limits set by the Environmental Protection Agency.

Microbial manganese(III) reduction fuelled by anaerobic acetate oxidation.

Soluble manganese in the intermediate +III oxidation state (Mn ) is a newly identified oxidant in anoxic environments, whereas acetate is a naturally abundant substrate that fuels microbial activity. Microbial populations coupling anaerobic acetate oxidation to Mn reduction, however, have yet to be identified. We isolated a Shewanella strain capable of oxidizing acetate anaerobically with Mn as the electron acceptor, and confirmed this phenotype in other strains.

Simultaneous Transformation of Commingled Trichloroethylene, Tetrachloroethylene, and 1,4-Dioxane by a Microbially Driven Fenton Reaction in Batch Liquid Cultures.

Unlabelled: Improper disposal of 1,4-dioxane and the chlorinated organic solvents trichloroethylene (TCE) and tetrachloroethylene (also known as perchloroethylene [PCE]) has resulted in widespread contamination of soil and groundwater. In the present study, a previously designed microbially driven Fenton reaction system was reconfigured to generate hydroxyl (HO˙) radicals for simultaneous transformation of source zone levels of single, binary, and ternary mixtures of TCE, PCE, and 1,4-dioxane. The reconfigured Fenton reaction system was driven by fed batch cultures of the Fe(III)-reducing facultative anaerobe Shewanella oneidensis amended with lactate, Fe(III), and contaminants and exposed to alternating anaerobic and aerobic conditions.

Direct conversion of cellulose and hemicellulose to fermentable sugars by a microbially-driven Fenton reaction.

The aim of this work was to develop a microbially-driven Fenton reaction that fragments cellulose and hemicellulose, degrades cellodextrins and xylodextrins, and produces short-chain oligosaccharides and monomeric sugars in a single bioreactor. The lignocellulose degradation system operates at neutral pH and does not require addition of conventional lignocellulose-degrading enzymes, thus avoiding problems associated with enzyme accessibility and specificity. The ability to produce useful bioproducts was demonstrated by production of the bioplastic polyhydroxybutyrate with the xylan degradation products as starting substrate.

Activation of an Otherwise Silent Xylose Metabolic Pathway in Shewanella oneidensis.

Unlabelled: Shewanella oneidensis is unable to metabolize the sugar xylose as a carbon and energy source. In the present study, an otherwise silent xylose catabolic pathway was activated in S. oneidensis by following an adaptive evolution strategy.

Electron transport and protein secretion pathways involved in Mn(III) reduction by Shewanella oneidensis.

Soluble Mn(III) represents an important yet overlooked oxidant in marine and freshwater systems. The molecular mechanism of microbial Mn(III) reduction, however, has yet to be elucidated. Extracellular reduction of insoluble Mn(IV) and Fe(III) oxides by the metal-reducing γ-proteobacterium Shewanella oneidensis involves inner (CymA) and outer (OmcA) membrane-associated c-type cytochromes, the extracellular electron conduit MtrCAB, and GspD, the secretin of type II protein secretion.

Microbially driven Fenton reaction for degradation of the widespread environmental contaminant 1,4-dioxane.

The carcinogenic cyclic ether compound 1,4-dioxane is employed as a stabilizer of chlorinated industrial solvents and is a widespread environmental contaminant in surface water and groundwater. In the present study, a microbially driven Fenton reaction was designed to autocatalytically generate hydroxyl (HO•) radicals that degrade 1,4-dioxane. In comparison to conventional (purely abiotic) Fenton reactions, the microbially driven Fenton reaction operated at circumneutral pH and did not the require addition of exogenous H2O2 or UV irradiation to regenerate Fe(II) as Fenton reagents.

Flow dependent performance of microfluidic microbial fuel cells.

The integration of Microbial Fuel Cells (MFCs) in a microfluidic geometry can significantly enhance the power density of these cells, which would have more active bacteria per unit volume. Moreover, microfluidic MFCs can be operated in a continuous mode as opposed to the traditional batch-fed mode. Here we investigate the effect of fluid flow on the performance of microfluidic MFCs.

Sulfur-mediated electron shuttling during bacterial iron reduction.

Microbial reduction of ferric iron [Fe(III)] is an important biogeochemical process in anoxic aquifers. Depending on groundwater pH, dissimilatory metal-reducing bacteria can also respire alternative electron acceptors to survive, including elemental sulfur (S(0)). To understand the interplay of Fe/S cycling under alkaline conditions, we combined thermodynamic geochemical modeling with bioreactor experiments using Shewanella oneidensis MR-1.

Identification of a molecular signature unique to metal-reducing Gammaproteobacteria.

Functional genes required for microbial (dissimilatory) metal reduction display high sequence divergence, which limits their utility as molecular biomarkers for tracking the presence and activity of metal-reducing bacteria in natural and engineered systems. In the present study, homologs of the outer membrane beta-barrel protein MtrB of metal-reducing Gammaproteobacteria were found to contain a unique N-terminal CXXC motif that was missing from MtrB homologs of nonmetal-reducing Gammaproteobacteria and metal- and nonmetal-reducing bacteria outside the Gammaproteobacteria. To determine whether the N-terminal CXXC motif of MtrB was required for dissimilatory metal reduction, each cysteine in the CXXC motif of the representative metal-reducing gammaproteobacterium Shewanella oneidensis was replaced with alanine, and the resulting site-directed mutants were tested for metal reduction activity.

Siderophores are not involved in Fe(III) solubilization during anaerobic Fe(III) respiration by Shewanella oneidensis MR-1.

Shewanella oneidensis MR-1 respires a wide range of anaerobic electron acceptors, including sparingly soluble Fe(III) oxides. In the present study, S. oneidensis was found to produce Fe(III)-solubilizing organic ligands during anaerobic Fe(III) oxide respiration, a respiratory strategy postulated to destabilize Fe(III) and produce more readily reducible soluble organic Fe(III).

Adhesion of Shewanella oneidensis MR-1 to iron (Oxy)(Hydr)oxides: microcolony formation and isotherm.

The adhesion of dissimilatory metal reducing bacteria (DMRB) to iron (oxy)(hydr)oxides may play an important role in their respiration on ferric iron-containing minerals, but few quantitative surface cell density measurements have been made thus far. We used confocal microscopy to examine the adhesion of a common DMRB species, Shewanella oneidensis MR-1, onto iron (oxy)(hydr)oxide particulate-coated glass slides across a broad range of bulk (i.e.

Shewanella oneidensis MR-1 mutants selected for their inability to produce soluble organic-Fe(III) complexes are unable to respire Fe(III) as anaerobic electron acceptor.

Recent voltammetric analyses indicate that Shewanella putrefaciens strain 200 produces soluble organic-Fe(III) complexes during anaerobic respiration of sparingly soluble Fe(III) oxides. Results of the present study expand the range of Shewanella species capable of producing soluble organic-Fe(III) complexes to include Shewanella oneidensis MR-1. Soluble organic-Fe(III) was produced by S.

Outer membrane-associated serine protease involved in adhesion of Shewanella oneidensis to Fe(III) oxides.

The facultative anaerobe Shewanella oneidensis MR-1 respires a variety of anaerobic electron acceptors, including insoluble Fe(III) oxides. S. oneidensis employs a number of novel strategies for respiration of insoluble Fe(III) oxides, including localization of respiratory proteins to the cell outer membrane (OM).

Anaerobic respiration of elemental sulfur and thiosulfate by Shewanella oneidensis MR-1 requires psrA, a homolog of the phsA gene of Salmonella enterica serovar typhimurium LT2.

Shewanella oneidensis MR-1, a facultatively anaerobic gammaproteobacterium, respires a variety of anaerobic terminal electron acceptors, including the inorganic sulfur compounds sulfite (SO3(2-)), thiosulfate (S2O3(2-)), tetrathionate (S4O6(2-)), and elemental sulfur (S(0)). The molecular mechanism of anaerobic respiration of inorganic sulfur compounds by S. oneidensis, however, is poorly understood.

Shewanella putrefaciens produces an Fe(III)-solubilizing organic ligand during anaerobic respiration on insoluble Fe(III) oxides.

The mechanism of Fe(III) reduction was investigated using voltammetric techniques in anaerobic incubations of Shewanella putrefaciens strain 200 supplemented with Fe(III) citrate or a suite of Fe(III) oxides as terminal electron acceptor. Results indicate that organic complexes of Fe(III) are produced during the reduction of Fe(III) at rates that correlate with the reactivity of the Fe(III) phase and bacterial cell density. Anaerobic Fe(III) solubilization activity is detected with either Fe(III) oxides or Fe(III) citrate, suggesting that the organic ligand produced is strong enough to destabilize Fe(III) from soluble or solid Fe(III) substrates.

Terminal electron acceptors influence the quantity and chemical composition of capsular exopolymers produced by anaerobically growing Shewanella spp.

Bacterial exopolymers perform various roles, including acting as a carbon sink, a protective layer against desiccation or antimicrobial agents, or a structural matrix in biofilms. Despite such varied roles, little is known about the heterogeneity of bacterial exopolymer production under varying growth conditions. Here we describe experiments designed to characterize the quantity and quality of exopolymers produced by two commonly studied members of the widely distributed genus Shewanella.

A conserved histidine in cytochrome c maturation permease CcmB of Shewanella putrefaciens is required for anaerobic growth below a threshold standard redox potential.

Shewanella putrefaciens strain 200 respires a wide range of compounds as terminal electron acceptor. The respiratory versatility of Shewanella is attributed in part to a set of c-type cytochromes with widely varying midpoint redox potentials (E'(0)). A point mutant of S.

A rapid mutant screening technique for detection of technetium [Tc(VII)] reduction-deficient mutants of Shewanella oneidensis MR-1.

Microbial metal reduction forms the basis of alternate bioremediation strategies for reductive precipitation and immobilization of toxic metals such as the radionuclide technetium [Tc(VII)]. A rapid mutant screening technique was developed to identify Shewanella oneidensis MR-1 respiratory mutants unable to reduce Tc(VII) as anaerobic electron acceptor. The Tc(VII) reduction-deficient (Tcr) mutant screening technique was based on the observation that wild-type S.