
Thomas DichristinaGeorgia Institute of Technology | GT · School of Biology
Thomas Dichristina
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Publications (93)
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 sens...
Microbial iodate (IO 3 – ) 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 3 – to iodide (I – ) and microbial methylation of I – to volatile gases. The met...
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 hum...
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. Our results provide the first evidence for biologi...
Shewanella drives a variety of environmentally important processes, including the biogeochemical cycling of carbon, metals, metalloids, and radionuclides. The ability of Shewanella to deliver electrons extracellularly also renders this genus valuable for applications of contaminant remediation and energy generation in water treatment processes. Alt...
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. Our results provide the first evidence for biolog...
Shewanella oneidensis respires a variety of terminal electron acceptors, including solid phase Fe(III) oxides. S. oneidensis transfers electrons to Fe(III) oxides via direct (outer membrane- or nanowire-localized c-type cytochromes) and indirect (electron shuttling and Fe(III) solubilization) pathways. In the present study, the influence of anaerob...
Microbial iodate (IO 3 ⁻ ) reduction is a major component in the biogeochemical cycling of iodine and the bioremediation of iodine-contaminated environments; however, the molecular mechanism of microbial IO 3 ⁻ reduction is poorly understood. Results of the present study indicate that outer membrane (type II) protein secretion and metal reduction g...
Microbial iodate (IO3⁻) reduction is a major component of iodine biogeochemical cycling and is the basis of alternative strategies for remediation of iodine-contaminated environments. The molecular mechanism of microbial IO3⁻ reduction, however, is not well understood. In several microorganisms displaying IO3⁻ and nitrate (NO3⁻) reduction activitie...
Previously, experimental DNA-DNA hybridization (DDH) between Shewanellahaliotis JCM 14758Tand Shewanellaalgae JCM 21037Thad 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. algae and S. haliotis, revealed...
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 comple...
Reactive Fe(III) minerals can influence methane (CH4) emissions by inhibiting microbial methanogenesis or by stimulating anaerobic CH4 oxidation. The balance between Fe(III) reduction, methanogenesis, and CH4 oxidation in ferruginous Archean and Paleoproterozoic oceans would have controlled CH4 fluxes to the atmosphere, thereby regulating the capac...
Reactive Fe(III) minerals can influence methane (CH 4 ) emissions by inhibiting microbial methanogenesis or by stimulating anaerobic CH 4 oxidation. The balance between Fe(III) reduction, methanogenesis, and methane oxidation in ferruginous Archean and Paleoproterozoic oceans would have controlled CH 4 fluxes to the atmosphere, thereby regulating t...
Importance:
A microbially-driven Fenton reaction system (driven by the Fe(III)-reducing facultative anaerobe S. oneidensis) was reconfigured to transform source zone levels of TCE, PCE, and 1,4-dioxane as single contaminants or as binary and ternary mixtures. The microbially-driven Fenton reaction may thus be applied as an ex situ platform for sim...
The in-situ detection of dissolved redox-active metals and metalloids such as iron and manganese is attracting increasing interest for understanding the complex network of enzymatic and geochemical reactions occurring at the microbe-mineral interface. A versatile and promising tool for the investigation of redox-active metal distributions at a micr...
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 conventiona...
Dissimilatory Fe(III)-reducing bacteria occupy a central position
in a variety of environmentally important processes,
including the biogeochemical cycling of carbon and iron,
the bioremediation of radionuclides and organohalides, and
the generation of electricity in microbial fuel cells (1–4). Fe
(III)-reducing bacteria are scattered and deeply ro...
Importance:
The activation of an otherwise silent xylose metabolic system in Shewanella oneidensis is a powerful example of how accidental mutations allow microorganisms to adaptively evolve. The expansion of the S. oneidensis metabolic repertoire to xylose expands the electron donors whose oxidation may be coupled to the myriad of terminal electr...
The ability to predict the success of the microbial reduction of soluble U(VI) to highly insoluble U(IV) as an in situ bioremediation strategy is complicated by the wide range of geochemical conditions at contaminated sites and the strong influence of aqueous uranyl speciation on the bioavailability and toxicity of U(VI) to metal-reducing bacteria....
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 c...
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 th...
How bacteria manage to breathe on rust
In the absence of oxygen, anaerobic bacteria turn to other chemical compounds during respiration. This can be helpful in detoxifying heavy-metal pollution. Flynn et al. (see the Perspective by Friedrich and Finster) found that alkaline conditions prevent a detoxifying bug— Shewanella oneidensis —from using enz...
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...
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-reduc...
Bioreduction, the microbial reduction of soluble U(VI) to highly insoluble U(IV), is considered one of the most promising in situ bioremediation strategies to immobilize uranium from groundwater. Although it has been demonstrated that Ca2+ and dissolved inorganic carbon (DIC) decrease bioreduction rates via the formation of stable U(VI)-carbonato a...
Mn(IV) and Mn(II) are the most stable and prevalent forms of manganese in natural environments. The occurrence of Mn(III) in minerals and the detection of soluble Mn(III) in natural waters, however, suggest that Mn(III) is an intermediate in both the oxidation of Mn(II) and the reduction of Mn(IV). Mn(III) has recently been proposed as an intermedi...
Bioremediation provides a unique in situ strategy for combating radioactive contamination from nuclear facilities. The most widely studied uranium bioremediation process revolves around the biotic reduction of aqueous U(VI) complexes to highly insoluble U(IV) minerals. Previous investigations highlighted the importance of uranium speciation on the...
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. S...
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...
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 redu...
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). The molecular mechanism by which S...
Shewanella oneidensis MR-1, a facultatively anaerobic gammaproteobacterium, respires a variety of anaerobic terminal electron acceptors, including
the inorganic sulfur compounds sulfite (SO32−), thiosulfate (S2O32−), tetrathionate (S4O62−), and elemental sulfur (S0). The molecular mechanism of anaerobic respiration of inorganic sulfur compounds by...
Atomic force microscopy was used to compare the dissolution morphology of iron (oxy)(hydr)oxide coated slides exposed to the dissimilatory iron reducing bacterium Shewanella oneidensis MR-1 and a Type II protein secretion mutant unable to reduce iron minerals without an exogenous electron shuttle. Dissolution morphologies of slides exposed to the w...
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 c...
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 design...
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. putrefaciens, originally designated Urr14 and here renamed CCMB1, was found to g...
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 acce...
Metal-reducing members of the genus Shewanella are important components of the microbial community residing in redox-strati.ed freshwater and marine environments. Metal-reducing
gram-negative bacteria such as Shewanella, however, are presented with a unique physiological challenge: they are required to respire anaerobically on terminal electron
acc...
Spatial and temporal trends in pore water geochemistry and sediment microbial community structure are compared at three intertidal sites of a saltmarsh on Sapelo Island, GA. The sites include a heavily bioturbated, unvegetated creek bank, a levee with dense growth of Spartina alterniflora, and a more sparsely vegetated ponded marsh site. The redox...
Metal-reducing members of the genus Shewanella are important components of the microbial community residing in redox-stratified freshwater and marine environments. Metal-reducing gram-negative bacteria such as Shewanella, however, are presented with a unique physiological challenge: they are required to respire anaerobically on terminal electron ac...
Dissimilatory metal-reducing bacteria (DMRB) are important components of the microbial community residing in redox-stratified freshwater and marine environments. DMRB occupy a central position in the biogeochemical cycles of metals, metalloids and radionuclides, and serve as catalysts for a variety of other environmentally important processes inclu...
Seasonal variations in anaerobic respiration pathways were investigated at three saltmarsh sites using chemical data, sulfate reduction rate measurements, enumerations of culturable populations of anaerobic iron-reducing bacteria (FeRB), and quantification of in situ 16S rRNA hybridization signals targeted for sulfate-reducing bacteria (SRB). Bacte...
Uranium Cycling
Iron Cycling
Manganese Cycling
Mercury Cycling
This chapter presents a variety of state-of-the-art molecular genetic approaches in bacteria with no natural genetic systems. Recent advances in molecular genetic techniques have provided powerful tools for elucidating the molecular basis of uncharacterized bacterial systems. Broad host range cloning systems are described as well as experimental st...
Shewanella putrefaciens, a heterotrophic member of the gamma-proteobacteria is capable of respiring anaerobically on Fe(III) as the sole terminal electron acceptor (TEA). Recent genetic and biochemical studies have indicated that anaerobic Fe(III) respiration by S. putrefaciens requires outer-membrane targeted secretion of respiration-linked Fe(III...
Shewanella putrefaciens strain 200 respires anaerobically on a wide range of compounds as the sole terminal electron acceptor, including ferric iron
[Fe(III)] and manganese oxide [Mn(IV)]. Previous studies demonstrated that a 23.3-kb S. putrefaciens wild-type DNA fragment conferred metal reduction capability to a set of respiratory mutants with imp...
We have conducted acid–base potentiometric titrations and U(VI) sorption experiments using the Gram negative, facultatively anaerobic bacterium Shewanella putrefaciens. Results of reversed titration studies on live, inactive bacteria indicate that their pH-buffering properties result from the equilibrium ionization of three discrete populations of...
A rapid screening technique for isolation of selenite (Se(IV)) reduction-deficient (Ser) mutants was developed and used to identify four Ser mutants of Shewanella putrefaciens. Two Ser mutants were unable to grow anaerobically on fumarate, nitrate or nitrite. Two other Ser mutants were unable to grow anaerobically on all compounds tested as sole te...
Shewanella putrefaciens was grown on a series of ten alternate compounds as sole terminal electron acceptor. Each cell type was analyzed for Fe(III) reduction activity, absorbance maxima in reduced-minus-oxidized difference spectra and heme-containing protein content. High-rate Fe(III) reduction activity, pronounced difference maxima at 521 and 551...
A U(VI) reduction-deficient mutant (Urr) screening technique was developed and combined with chemical mutagenesis procedures to identify a Urr mutant of Shewanella putrefaciens strain 200. The Urr mutant lacked the ability to grow anaerobically on U(VI) and NO(2)(-), yet retained the ability to grow anaerobically on eight other compounds as termina...
Population densities of anaerobic Fe(III)-reducing bacteria (FeRB) and aerobic heterotrophs were inversely correlated in the surficial (0-2 cm) layers of Sapelo Island, Georgia, salt marsh sediments. In surficial sediments where densities of aerobic heterotrophs were low, the density of culturable FeRB correlated positively with the concentration o...
A microbially driven transformation system was developed for the oxidative degradation of pentachlorophenol (PCP). The system was based on a free radical-generating Fenton reaction between bacterially produced Fe(II) and H{sub 2}O{sub 2}. The Fe(III)-reducing, facultative anaerobe Shewanella putrefaciens strain 200 was used as a catalyst for both F...
Chemical distributions and microbial culture data are combined to identify the biogeochemical pathways that control the cycles of manganese and iron at the oxic−anoxic transition of the Orca Basin. The redox transition coincides with an increase in salinity from 35 to 260‰; hence, mixing diagrams are used to constrain the salinity ranges over which...
Chemical mutagenesis procedures and two newly developed rapid plate assays were used to identify two Mn(IV) reduction-deficient (Mnr) mutants of Shewanella putrefaciens. All eleven members of a set of previously isolated Fe(III) reduction-deficient (Fer) mutants displayed Mnr-positive phenotypes on the plate assays and were also capable of anaerobi...
This experimental study investigated the processes by which microbes interact with oxyhydroxide mineral surface coatings using an approach designed to better represent the conditions of natural subsurface environments. The interactions of Shewanella putrefaciens, a facultative anaerobe capable of dissimilatory iron reduction, with coatings of Fe³⁺...
Pleiotropic respiratory mutants, incapable of growth on any electron acceptor other than oxygen, were isolated from two strains of Shewanella putrefaciens (MR-1 and sp200). All anaerobic respiratory functions were restored by complementation of the mutants with specific cloned DNA fragments. Southern hybridization experiments revealed that the frag...
Results of the present study indicate that S. putrefaciens 200 may be a suitable Fe(3+)-reducing microorganism for commercial application in a microbially catalyzed iron ore bioextraction (reductive dissolution) process. The proposed scheme of the bioextraction process (Fig. 1) entails the addition of a suitable iron ore to anaerobic, batch culture...
A genetic approach was used to study (dissimilatory) ferric iron (Fe3+) reduction in Shewanella putrefaciens 200. Chemical mutagenesis procedures and two rapid plate assays were developed to facilitate the screening of Fe3+ reduction-deficient mutants. Sixty-two putative Fe3+ reduction-deficient mutants were identified, and each was subsequently te...
A 16S rRNA-targeted oligonucleotide probe specific for the iron (Fe3+)- and manganese (Mn4+)-reducing bacterium Shewanella putrefaciens was constructed and tested in both laboratory- and field-based hybridization experiments. The radioactively labeled probe was used to detect S. putrefaciens in field samples collected from the water column and sedi...
The inhibitory effects of nitrate (NO3-) and nitrite (NO2-) on dissimilatory iron (FE3+) reduction were examined in a series of electron acceptor competition experiments using Shewanella putrefaciens 200 as a model iron-reducing microorganism. S. putrefaciens 200 was found to express low-rate nitrate reductase, nitrite reductase, and ferrireductase...
Under anaerobic conditions, Shewanella putrefaciens is capable of respiratory-chain-linked, high-rate dissimilatory iron reduction via both a constitutive and inducible Fe(III)-reducing system. In the presence of low levels of dissolved oxygen, however, iron reduction by this microorganism is extremely slow. Fe(II)-trapping experiments in which Fe(...
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Complementary genetic and biochemical analyses have been used to study the (dissimilative) iron reduction system of Alteromonas putrefaciens strain 200. Preliminary kinetic data suggested that A. putrefaciens 200 possessed a ferri-redu...
The ability of microorganisms to mediate the transformation of iron coupled with the participation of iron as a reactive redox species in natural waters and sediments has prompted recent speculation that such bacteria play an important role in such activities as global iron cycling, biologically induced mineral formation, and localized competition...
The kinetics and mechanism of reductive dissolution of Fe(III) oxides were examined in pure, batch cultures of Pseudomonassp. 200. Primary factors controlling hematite dissolution kinetics were mineral surface area (or concentration of high-energy surface sites), ligand concentration, and cell number. In the presence of nitrilotriacetic acid (NTA),...
Aerobic respiration and dissimilative iron reduction were studied in pure, batch cultures of Pseudomonas sp. strain 200 ("Pseudomonas ferrireductans"). Specific respiratory inhibitors were used to identify elements of electron transport chains involved in the reduction of molecular oxygen and Fe(III). When cells were grown at a high oxygen concentr...
Light scattering and photon correlation spectroscopy have been utilized in studying the effect of the surfactant chemical nature on micellar interactions in W/O microemulsions. Specifically, the surfactant chemical structure has been altered at the molecular level by adding a ramification near the polar head group. This influence of surfactant stru...
The feasibilities of (1) liberating free energy from dissimilative iron reduction and (2) coupling oxidative phosphorylation to electron transport to Fe(III) are sensitive to the aqueous chemistry of Fe(III). A systematic investigation of iron-reduction kinetics as a function of Fe(III) speciation indicated that in Pseudomonas sp. 200 (1) iron-redu...