1
|
Karadagli F, Marcus A, Rittmann BE. Microbiological hydrogen (H 2 ) thresholds in anaerobic continuous-flow systems: Effects of system characteristics. Biotechnol Bioeng 2023. [PMID: 37148477 DOI: 10.1002/bit.28415] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 03/20/2023] [Accepted: 04/24/2023] [Indexed: 05/08/2023]
Abstract
Hydrogen (H2 ) concentrations that were associated with microbiological respiratory processes (RPs) such as sulfate reduction and methanogenesis were quantified in continuous-flow systems (CFSs) (e.g., bioreactors, sediments). Gibbs free energy yield (ΔǴ ~ 0) of the relevant RP has been proposed to control the observed H2 concentrations, but most of the reported values do not align with the proposed energetic trends. Alternatively, we postulate that system characteristics of each experimental design influence all system components including H2 concentrations. To analyze this proposal, a Monod-based mathematical model was developed and used to design a gas-liquid bioreactor for hydrogenotrophic methanogenesis with Methanobacterium bryantii M.o.H. Gas-to-liquid H2 mass transfer, microbiological H2 consumption, biomass growth, methane formation, and Gibbs free energy yields were evaluated systematically. Combining model predictions and experimental results revealed that an initially large biomass concentration created transients during which biomass consumed [H2 ]L rapidly to the thermodynamic H2 -threshold (≤1 nM) that triggerred the microorganisms to stop H2 oxidation. With no H2 oxidation, continuous gas-to-liquid H2 transfer increased [H2 ]L to a level that signaled the methanogens to resume H2 oxidation. Thus, an oscillatory H2 -concentration profile developed between the thermodynamic H2 -threshold (≤1 nM) and a low [H2 ]L (~10 nM) that relied on the rate of gas-to-liquid H2 -transfer. The transient [H2 ]L values were too low to support biomass synthesis that could balance biomass losses through endogenous oxidation and advection; thus, biomass declined continuously and disappeared. A stable [H2 ]L (1807 nM) emerged as a result of abiotic H2 -balance between gas-to-liquid H2 transfer and H2 removal via advection of liquid-phase.
Collapse
Affiliation(s)
- Fatih Karadagli
- Biodesign Swette Center for Environmental Biotechnology, Arizona State University, Tempe, Arizona, USA
| | - Andrew Marcus
- Biodesign Swette Center for Environmental Biotechnology, Arizona State University, Tempe, Arizona, USA
- Skyology Inc., San Francisco, California, USA
| | - Bruce E Rittmann
- Biodesign Swette Center for Environmental Biotechnology, Arizona State University, Tempe, Arizona, USA
| |
Collapse
|
2
|
Cooper RE, Finck J, Chan C, Küsel K. Mixotrophy broadens the ecological niche range of the iron oxidizer Sideroxydans sp. CL21 isolated from an iron-rich peatland. FEMS Microbiol Ecol 2023; 99:6979798. [PMID: 36623865 PMCID: PMC9925335 DOI: 10.1093/femsec/fiac156] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 11/17/2022] [Accepted: 01/06/2023] [Indexed: 01/11/2023] Open
Abstract
Sideroxydans sp. CL21 is a microaerobic, acid-tolerant Fe(II)-oxidizer, isolated from the Schlöppnerbrunnen fen. Since the genome size of Sideroxydans sp. CL21 is 21% larger than that of the neutrophilic Sideroxydans lithotrophicus ES-1, we hypothesized that strain CL21 contains additional metabolic traits to thrive in the fen. The common genomic content of both strains contains homologs of the putative Fe(II) oxidation genes, mtoAB and cyc2. A large part of the accessory genome in strain CL21 contains genes linked to utilization of alternative electron donors, including NiFe uptake hydrogenases, and genes encoding lactate uptake and utilization proteins, motility and biofilm formation, transposable elements, and pH homeostasis mechanisms. Next, we incubated the strain in different combinations of electron donors and characterized the fen microbial communities. Sideroxydans spp. comprised 3.33% and 3.94% of the total relative abundance in the peatland soil and peatland water, respectively. Incubation results indicate Sideroxydans sp. CL21 uses H2 and thiosulfate, while lactate only enhances growth when combined with Fe, H2, or thiosulfate. Rates of H2 utilization were highest in combination with other substrates. Thus, Sideroxydans sp. CL21 is a mixotroph, growing best by simultaneously using substrate combinations, which helps to thrive in dynamic and complex habitats.
Collapse
Affiliation(s)
- Rebecca E Cooper
- Aquatic Geomicrobiology, Institute of Biodiversity, Friedrich Schiller University Jena, 07743 Jena, Germany
| | - Jessica Finck
- Aquatic Geomicrobiology, Institute of Biodiversity, Friedrich Schiller University Jena, 07743 Jena, Germany
| | - Clara Chan
- School of Marine Science and Policy, University of Delaware, Newark, DE 19716, United States,Delaware Biotechnology Institute, University of Delaware, Newark, DE 19713, United States,Department of Earth Sciences, University of Delaware, Newark, DE 19716, United States
| | - Kirsten Küsel
- Corresponding author. Institute of Biodiversity, Friedrich Schiller University Jena, Dornburger Str. 159, 07743 Jena, Germany. Tel: +49 3641 949461; Fax: +49 3641 949462; E-mail:
| |
Collapse
|
3
|
Scarabotti F, Bühler K, Schmidt M, Harnisch F. Thickness and roughness of transparent gold-palladium anodes have no impact on growth kinetics and yield coefficients of early-stage Geobacter sulfurreducens biofilms. Bioelectrochemistry 2022; 144:108043. [PMID: 34959027 DOI: 10.1016/j.bioelechem.2021.108043] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 11/24/2021] [Accepted: 12/13/2021] [Indexed: 01/05/2023]
Abstract
Geobacter sulfurreducens is the model organism for electroactive microorganisms performing direct extracellular electron transfer and forming thick mature biofilm electrodes. Although numerous physiological properties of mature biofilm electrodes are deciphered, there is an extensive gap of knowledge on the early-stage biofilm formation. We have shown recently that transparent gold-palladium (AuPd) electrodes allow for analysis of early-stage biofilm formation using confocal laser scanning microscopy. Here we analysed the influence of thickness (ranging from 12.5 to 200 nm) and roughness of AuPd electrodes on physiological parameters of G. sulfurreducens early-stage biofilms. We show that when grown potentiostatically at -200 mV vs. Ag/ AgCl sat. KCl neither maximum current density (jmax of ∼ 80-150 µA cm-2) nor lag time (lag t of ∼ 0.2-0.4 days) or single cell yield coefficients (YNe of 1.43 × 1012 cells mole--1) of the biofilms are influenced by the electrode preparation. This confirms the robustness of the experimental approach, which is an inevitable prerequisite for obtaining reliable results in follow-up experiments.
Collapse
Affiliation(s)
- Francesco Scarabotti
- Department of Environmental Microbiology, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Katja Bühler
- Department Solar Materials, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Matthias Schmidt
- Department of Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Falk Harnisch
- Department of Environmental Microbiology, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany.
| |
Collapse
|
4
|
Multiscale Modeling of Uranium Bioreduction in Porous Media by One-Dimensional Biofilms. Bull Math Biol 2021; 83:105. [PMID: 34477982 DOI: 10.1007/s11538-021-00938-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 08/16/2021] [Indexed: 10/20/2022]
Abstract
We formulate a multiscale mathematical model that describes the bioreduction of uranium in porous media. On the mesoscale we describe the bioreduction of uranium [VI] to uranium [IV] using a multispecies one-dimensional biofilm model with suspended bacteria and thermodynamic growth inhibition. We upscale the mesoscopic (colony scale) model to the macroscale (reactor scale) and investigate the behavior of substrate utilization and production, attachment and detachment processes, and thermodynamic effects not usually considered in biofilm growth models. Simulation results of the reactor model indicate that thermodynamic inhibition quantitatively alters the dynamics of the model and neglecting thermodynamic effects may over- or underestimate chemical concentrations in the system. Furthermore, we numerically investigate uncertainties related to the specific choice of attachment and detachment rate coefficients and find that while increasing the attachment rate coefficient or decreasing the detachment rate coefficient leads to thicker biofilms, performance of the reactor remains largely unaffected.
Collapse
|
5
|
Yan Y, Wang X, Askari A, Lee HS. A modelling study of the spatially heterogeneous mutualism between electroactive biofilm and planktonic bacteria. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 759:143537. [PMID: 33272602 DOI: 10.1016/j.scitotenv.2020.143537] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Revised: 10/27/2020] [Accepted: 10/29/2020] [Indexed: 06/12/2023]
Abstract
Microbial cooperation widely exists in anaerobic reactors degrading complex pollutants, conventionally studied separately inside the biofilm or the planktonic community. Recent experiments discovered the mutualism between the planktonic bacteria and electroactive biofilm treating propionate, an end-product usually accumulated in anaerobic digesters. Here, a one-dimensional multispecies model found the preference on acetate-based pathway over the hydrogen-based in such community, evidenced by the fact that acetate-originated current takes 66% of the total value and acetate-consuming anode-respiring bacteria takes over 80% of the biofilm. Acetate-based anodic respiration most apparently influences biofilm function while propionate fermentation is the dominant planktonic bio-reaction. Additionally, initial planktonic propionate level shows the ability of coordinating the balance between these two extracellular electron transfer pathways. Increasing the propionate concentration from 2 to 50 mM would increase the steady hydrogen-originated current by 210% but decrease the acetate-originated by 26%, suggesting a vital influence of the planktonic microbial process to the metabolic balance in biofilm. Best strategy to promote the biofilm activity is to increase the biomass density and biofilm conductivity simultaneously, which would increase the current density by 875% without thickening the biofilm thickness or prolonging the growth apparently.
Collapse
Affiliation(s)
- Yuqing Yan
- MOE Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Key Laboratory of Environmental Remediation and Pollution Control/College of Environmental Science and Engineering, Nankai University, No. 38 Tongyan Road, Jinnan District, Tianjin 300350, China
| | - Xin Wang
- MOE Key Laboratory of Pollution Processes and Environmental Criteria/Tianjin Key Laboratory of Environmental Remediation and Pollution Control/College of Environmental Science and Engineering, Nankai University, No. 38 Tongyan Road, Jinnan District, Tianjin 300350, China
| | - Anis Askari
- Department of Civil & Environmental Engineering/Department of Chemical Engineering, The University of Waterloo, 200 University Ave W, Waterloo, ON N2L 3G1, Canada
| | - Hyung-Sool Lee
- Department of Civil & Environmental Engineering/Department of Chemical Engineering, The University of Waterloo, 200 University Ave W, Waterloo, ON N2L 3G1, Canada.
| |
Collapse
|
6
|
Scarabotti F, Rago L, Bühler K, Harnisch F. The electrode potential determines the yield coefficients of early-stage Geobacter sulfurreducens biofilm anodes. Bioelectrochemistry 2021; 140:107752. [PMID: 33618189 DOI: 10.1016/j.bioelechem.2021.107752] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 01/29/2021] [Accepted: 01/30/2021] [Indexed: 01/05/2023]
Abstract
Geobacter sulfurreducens is the model for electroactive microorganisms (EAM). EAM can use solid state terminal electron acceptors (TEA) including anodes via extracellular electron transfer (EET). Yield coefficients relate the produced cell number or biomass to the oxidized substrate or the reduced TEA. These data are not yet sufficiently available for EAM growing at anodes. Thus, this study provides information about kinetics as well as yield coefficients of early-stage G. sulfurreducens biofilms using anodes as TEA at the potentials of -200 mV, 0 mV and +200 mV (vs. Ag/AgCl sat. KCl). The selected microorganism was therefore cultivated in single and double chamber batch reactors on graphite or AuPd anodes. Interestingly, whereas the lag time and maximum current density within 12 days of growth differed, the anode potential does not influence the coulombic efficiency and the formal potential of the EET, which remains constant for all the experiments at ~ -300 to -350 mV. We demonstrated for the first time that the anode potential has a strong influence on single cell yield coefficients which ranged from 2.69 × 1012 cells mole--1 at -200 mV and 1.48 × 1012 cells mole--1 at 0 mV to 2.58 × 1011 cells mole--1 at +200 mV in single chamber reactors and from 1.15 × 1012 cells mole--1 at -200 mV to 8.98× 1011 cells mole--1 at 0 mV in double chamber reactors. This data can be useful for optimization and scaling-up of primary microbial electrochemical technologies.
Collapse
Affiliation(s)
- Francesco Scarabotti
- Department of Environmental Microbiology, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Laura Rago
- Department of Environmental Microbiology, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Katja Bühler
- Department Solar Materials, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Falk Harnisch
- Department of Environmental Microbiology, Helmholtz-Centre for Environmental Research - UFZ, Leipzig, Germany.
| |
Collapse
|
7
|
Satinover SJ, Rodriguez M, Campa MF, Hazen TC, Borole AP. Performance and community structure dynamics of microbial electrolysis cells operated on multiple complex feedstocks. BIOTECHNOLOGY FOR BIOFUELS 2020; 13:169. [PMID: 33062055 PMCID: PMC7552531 DOI: 10.1186/s13068-020-01803-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 09/20/2020] [Indexed: 06/11/2023]
Abstract
BACKGROUND Microbial electrolysis is a promising technology for converting aqueous wastes into hydrogen. However, substrate adaptability is an important feature, seldom documented in microbial electrolysis cells (MECs). In addition, the correlation between substrate composition and community structure has not been well established. This study used an MEC capable of producing over 10 L/L-day of hydrogen from a switchgrass-derived bio-oil aqueous phase and investigated four additional substrates, tested in sequence on a mature biofilm. The additional substrates included a red oak-derived bio-oil aqueous phase, a corn stover fermentation product, a mixture of phenol and acetate, and acetate alone. RESULTS The MECs fed with the corn stover fermentation product resulted in the highest performance among the complex feedstocks, producing an average current density of 7.3 ± 0.51 A/m2, although the acetate fed MECs outperformed complex substrates, producing 12.3 ± 0.01 A/m2. 16S rRNA gene sequencing showed that community structure and community diversity were not predictive of performance, and replicate community structures diverged despite identical inoculum and enrichment procedure. The trends in each replicate, however, were indicative of the influence of the substrates. Geobacter was the most dominant genus across most of the samples tested, but its abundance did not correlate strongly to current density. High-performance liquid chromatography (HPLC) showed that acetic acid accumulated during open circuit conditions when MECs were fed with complex feedstocks and was quickly degraded once closed circuit conditions were applied. The largest net acetic acid removal rate occurred when MECs were fed with red oak bio-oil aqueous phase, consuming 2.93 ± 0.00 g/L-day. Principal component analysis found that MEC performance metrics such as current density, hydrogen productivity, and chemical oxygen demand removal were closely correlated. Net acetic acid removal was also found to correlate with performance. However, no bacterial genus appeared to correlated to these performance metrics strongly, and the analysis suggested that less than 70% of the variance was accounted for by the two components. CONCLUSIONS This study demonstrates the robustness of microbial communities to adapt to a range of feedstocks and conditions without relying on specific species, delivering high hydrogen productivities despite differences in community structure. The results indicate that functional adaptation may play a larger role in performance than community composition. Further investigation of the roles each microbe plays in these communities will help MECs to become integral in the 21st-century bioeconomy to produce zero-emission fuels.
Collapse
Affiliation(s)
- Scott J. Satinover
- Bredesen Center for Interdisciplinary Research and Education, The University of Tennessee, Knoxville, USA
| | - Miguel Rodriguez
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Maria F. Campa
- Institute for a Secure & Sustainable Environment, The University of Tennessee, Knoxville, USA
| | - Terry C. Hazen
- Bredesen Center for Interdisciplinary Research and Education, The University of Tennessee, Knoxville, USA
- Civil and Environmental Engineering, The University of Tennessee, Knoxville, USA
- Institute for a Secure & Sustainable Environment, The University of Tennessee, Knoxville, USA
| | - Abhijeet P. Borole
- Bredesen Center for Interdisciplinary Research and Education, The University of Tennessee, Knoxville, USA
- Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, USA
| |
Collapse
|
8
|
Szeinbaum N, Nunn BL, Cavazos AR, Crowe SA, Stewart FJ, DiChristina TJ, Reinhard CT, Glass JB. Novel insights into the taxonomic diversity and molecular mechanisms of bacterial Mn(III) reduction. ENVIRONMENTAL MICROBIOLOGY REPORTS 2020; 12:583-593. [PMID: 32613749 PMCID: PMC7775658 DOI: 10.1111/1758-2229.12867] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 06/27/2020] [Accepted: 06/29/2020] [Indexed: 05/23/2023]
Abstract
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 the biological reduction of soluble Mn(III) outside the Gammaproteobacteria. Metagenome assembly and binning revealed a novel betaproteobacterium, which we designate 'Candidatus Dechloromonas occultata.' This organism dominated the enrichment and expressed a porin-cytochrome c complex typically associated with iron-oxidizing Betaproteobacteria and a novel cytochrome c-rich protein cluster (Occ), including an undecaheme putatively involved in extracellular electron transfer. This occ gene cluster was also detected in diverse aquatic bacteria, including uncultivated Betaproteobacteria from the deep subsurface. These observations provide new insight into the taxonomic and functional diversity of microbially driven Mn(III) reduction in natural environments.
Collapse
Affiliation(s)
- Nadia Szeinbaum
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- NASA Astrobiology Institute, Alternative Earths Team, Mountain View, CA, USA
| | - Brook L. Nunn
- Department of Genome Sciences, University of Washington, Seattle, WA, USA
| | - Amanda R. Cavazos
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - Sean A. Crowe
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Frank J. Stewart
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT, USA
| | | | - Christopher T. Reinhard
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- NASA Astrobiology Institute, Alternative Earths Team, Mountain View, CA, USA
| | - Jennifer B. Glass
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- NASA Astrobiology Institute, Alternative Earths Team, Mountain View, CA, USA
| |
Collapse
|
9
|
Gaebler HJ, Eberl HJ. Thermodynamic Inhibition in Chemostat Models : With an Application to Bioreduction of Uranium. Bull Math Biol 2020; 82:76. [PMID: 32535693 DOI: 10.1007/s11538-020-00758-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 05/30/2020] [Indexed: 10/24/2022]
Abstract
We formulate a mathematical model of bacterial populations in a chemostat setting that also accounts for thermodynamic growth inhibition as a consequence of chemical reactions. Using only elementary mathematical and chemical arguments, we carry this out for two systems: a simple toy model with a single species, a single substrate, and a single reaction product, and a more involved model that describes bioreduction of uranium[VI] into uranium[IV]. We find that in contrast to most traditional chemostat models, as a consequence of thermodynamic inhibition the equilibria concentrations of nutrient substrates might depend on their inflow concentration and not only on reaction parameters and the reactor's dilution rate. Simulation results of the uranium degradation model indicate that thermodynamic growth inhibition quantitatively alters the solution of the model. This suggests that neglecting thermodynamic inhibition effects in systems where they play a role might lead to wrong model predictions and under- or over-estimate the efficacy of the process under investigation.
Collapse
|
10
|
Quantification of microaerobic growth of Geobacter sulfurreducens. PLoS One 2020; 15:e0215341. [PMID: 31945063 PMCID: PMC6964889 DOI: 10.1371/journal.pone.0215341] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Accepted: 12/30/2019] [Indexed: 12/22/2022] Open
Abstract
Geobacter sulfurreducens was originally considered a strict anaerobe. However, this bacterium was later shown to not only tolerate exposure to oxygen but also to use it as terminal electron acceptor. Research performed has so far only revealed the general ability of G. sulfurreducens to reduce oxygen, but the oxygen uptake rate has not been quantified yet, nor has evidence been provided as to how the bacterium achieves oxygen reduction. Therefore, microaerobic growth of G. sulfurreducens was investigated here with better defined operating conditions as previously performed and a transcriptome analysis was performed to elucidate possible metabolic mechanisms important for oxygen reduction in G. sulfurreducens. The investigations revealed that cell growth with oxygen is possible to the same extent as with fumarate if the maximum specific oxygen uptake rate (sOUR) of 95 mgO2 gCDW-1 h-1 is not surpassed. Hereby, the entire amount of introduced oxygen is reduced. When oxygen concentrations are too high, cell growth is completely inhibited and there is no partial oxygen consumption. Transcriptome analysis suggests a menaquinol oxidase to be the enzyme responsible for oxygen reduction. Transcriptome analysis has further revealed three different survival strategies, depending on the oxygen concentration present. When prompted with small amounts of oxygen, G. sulfurreducens will try to escape the microaerobic area; if oxygen concentrations are higher, cells will focus on rapid and complete oxygen reduction coupled to cell growth; and ultimately cells will form protective layers if a complete reduction becomes impossible. The results presented here have important implications for understanding how G. sulfurreducens survives exposure to oxygen.
Collapse
|
11
|
Engel C, Schattenberg F, Dohnt K, Schröder U, Müller S, Krull R. Long-Term Behavior of Defined Mixed Cultures of Geobacter sulfurreducens and Shewanella oneidensis in Bioelectrochemical Systems. Front Bioeng Biotechnol 2019; 7:60. [PMID: 30972336 PMCID: PMC6445848 DOI: 10.3389/fbioe.2019.00060] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 03/05/2019] [Indexed: 11/24/2022] Open
Abstract
This work aims to investigate the long-term behavior of interactions of electrochemically active bacteria in bioelectrochemical systems. The electrochemical performance and biofilm characteristics of pure cultures of Geobacter sulfurreducens and Shewanella oneidensis are being compared to a defined mixed culture of both organisms. While S. oneidensis pure cultures did not form cohesive and stable biofilms on graphite anodes and only yielded 0.034 ± 0.011 mA/cm2 as maximum current density by feeding of each 5 mM lactate and acetate, G. sulfurreducens pure cultures formed 69 μm thick, area-wide biofilms with 10 mM acetate as initial substrate concentration and yielded a current of 0.39 ± 0.09 mA/cm2. Compared to the latter, a defined mixed culture of both species was able to yield 38% higher maximum current densities of 0.54 ± 0.07 mA/cm2 with each 5 mM lactate and acetate. This increase in current density was associated with a likewise increased thickness of the anodic biofilm to approximately 93 μm. It was further investigated whether a sessile incorporation of S. oneidensis into the mixed culture biofilm, which has been reported previously for short-term experiments, is long-term stable. The results demonstrate that S. oneidensis was not stably incorporated into the biofilm; rather, the planktonic presence of S. oneidensis has a positive effect on the biofilm growth of G. sulfurreducens and thus on current production.
Collapse
Affiliation(s)
- Christina Engel
- Institute of Biochemical Engineering, Technische Universität Braunschweig, Braunschweig, Germany.,Braunschweig Centre of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany
| | - Florian Schattenberg
- Working Group Flow Cytometry, Department of Environmental Microbiology, Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Katrin Dohnt
- Institute of Biochemical Engineering, Technische Universität Braunschweig, Braunschweig, Germany.,Braunschweig Centre of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany
| | - Uwe Schröder
- Braunschweig Centre of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany.,Institute of Environmental and Sustainable Chemistry, Technische Universität Braunschweig, Braunschweig, Germany
| | - Susann Müller
- Working Group Flow Cytometry, Department of Environmental Microbiology, Centre for Environmental Research - UFZ, Leipzig, Germany
| | - Rainer Krull
- Institute of Biochemical Engineering, Technische Universität Braunschweig, Braunschweig, Germany.,Braunschweig Centre of Systems Biology (BRICS), Technische Universität Braunschweig, Braunschweig, Germany
| |
Collapse
|
12
|
Kinetic competition between microbial anode respiration and nitrate respiration in a bioelectrochemical system. Bioelectrochemistry 2018; 123:241-247. [DOI: 10.1016/j.bioelechem.2018.06.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 05/30/2018] [Accepted: 06/01/2018] [Indexed: 12/07/2022]
|
13
|
Pal DS, Tripathee R, Reid MC, Schäfer KVR, Jaffé PR. Simultaneous measurements of dissolved CH 4 and H 2 in wetland soils. ENVIRONMENTAL MONITORING AND ASSESSMENT 2018; 190:176. [PMID: 29484491 DOI: 10.1007/s10661-018-6552-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2017] [Accepted: 02/12/2018] [Indexed: 06/08/2023]
Abstract
Biogeochemical processes in wetland soils are complex and are driven by a microbiological community that competes for resources and affects the soil chemistry. Depending on the availability of various electron acceptors, the high carbon input to wetland soils can make them important sources of methane production and emissions. There are two significant pathways for methanogenesis: acetoclastic and hydrogenotrophic methanogenesis. The hydrogenotrophic pathway is dependent on the availability of dissolved hydrogen gas (H2), and there is significant competition for available H2. This study presents simultaneous measurements of dissolved methane and H2 over a 2-year period at three tidal marshes in the New Jersey Meadowlands. Methane reservoirs show a significant correlation with dissolved organic carbon, temperature, and methane emissions, whereas the H2 concentrations measured with dialysis samplers do not show significant relationships with these field variables. Data presented in this study show that increased dissolved H2 reservoirs in wetland soils correlate with decreased methane reservoirs, which is consistent with studies that have shown that elevated levels of H2 inhibit methane production by inhibiting propionate fermentation, resulting in less acetate production and hence decreasing the contribution of acetoclastic methanogenesis to the overall production of methane.
Collapse
Affiliation(s)
- David S Pal
- Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, USA
| | - Rajan Tripathee
- Department of Biological Sciences, Rutgers University, Newark, NJ, USA
| | - Matthew C Reid
- School of Civil and Environmental Engineering, Cornell University, Ithaca, NY, USA
| | | | - Peter R Jaffé
- Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, USA.
| |
Collapse
|
14
|
Modeling multidimensional and multispecies biofilms in porous media. Biotechnol Bioeng 2017; 114:1679-1687. [DOI: 10.1002/bit.26292] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2016] [Revised: 03/12/2017] [Accepted: 03/15/2017] [Indexed: 11/07/2022]
|
15
|
Liu J, Hou H, Chen X, Bazan GC, Kashima H, Logan BE. Conjugated oligoelectrolyte represses hydrogen oxidation by Geobacter sulfurreducens in microbial electrolysis cells. Bioelectrochemistry 2015; 106:379-82. [DOI: 10.1016/j.bioelechem.2015.07.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 06/27/2015] [Accepted: 07/08/2015] [Indexed: 11/28/2022]
|
16
|
Siegert M, Li XF, Yates MD, Logan BE. The presence of hydrogenotrophic methanogens in the inoculum improves methane gas production in microbial electrolysis cells. Front Microbiol 2015; 5:778. [PMID: 25642216 PMCID: PMC4295556 DOI: 10.3389/fmicb.2014.00778] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 12/18/2014] [Indexed: 11/26/2022] Open
Abstract
High current densities in microbial electrolysis cells (MECs) result from the predominance of various Geobacter species on the anode, but it is not known if archaeal communities similarly converge to one specific genus. MECs were examined here on the basis of maximum methane production and current density relative to the inoculum community structure. We used anaerobic digester (AD) sludge dominated by acetoclastic Methanosaeta, and an anaerobic bog sediment where hydrogenotrophic methanogens were detected. Inoculation using solids to medium ratio of 25% (w/v) resulted in the highest methane production rates (0.27 mL mL−1 cm−2, gas volume normalized by liquid volume and cathode projected area) and highest peak current densities (0.5 mA cm−2) for the bog sample. Methane production was independent of solid to medium ratio when AD sludge was used as the inoculum. 16S rRNA gene community analysis using pyrosequencing and quantitative PCR confirmed the convergence of Archaea to Methanobacterium and Methanobrevibacter, and of Bacteria to Geobacter, despite their absence in AD sludge. Combined with other studies, these findings suggest that Archaea of the hydrogenotrophic genera Methanobacterium and Methanobrevibacter are the most important microorganisms for methane production in MECs and that their presence in the inoculum improves the performance.
Collapse
Affiliation(s)
- Michael Siegert
- Department of Civil and Environmental Engineering, Penn State University University Park, PA, USA
| | - Xiu-Fen Li
- School of Environmental and Civil Engineering, Jiangnan University Wuxi, China
| | - Matthew D Yates
- Department of Civil and Environmental Engineering, Penn State University University Park, PA, USA
| | - Bruce E Logan
- Department of Civil and Environmental Engineering, Penn State University University Park, PA, USA
| |
Collapse
|
17
|
Zhu X, Yates MD, Hatzell MC, Ananda Rao H, Saikaly PE, Logan BE. Microbial community composition is unaffected by anode potential. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:1352-1358. [PMID: 24364567 DOI: 10.1021/es404690q] [Citation(s) in RCA: 102] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
There is great controversy on how different set anode potentials affect the performance of a bioelectrochemical system (BES). It is often reported that more positive potentials improve acclimation and performance of exoelectrogenic biofilms, and alter microbial community structure, while in other studies relatively more negative potentials were needed to achieve higher current densities. To address this issue, the biomass, electroactivity, and community structure of anodic biofilms were examined over a wide range of set anode potentials (-0.25, -0.09, 0.21, 0.51, and 0.81 V vs a standard hydrogen electrode, SHE) in single-chamber microbial electrolysis cells. Maximum currents produced using a wastewater inoculum increased with anode potentials in the range of -0.25 to 0.21 V, but decreased at 0.51 and 0.81 V. The maximum currents were positively correlated with increasing biofilm biomass. Pyrosequencing indicated biofilm communities were all similar and dominated by bacteria most similar to Geobacter sulfurreducens. Differences in anode performance with various set potentials suggest that the exoelectrogenic communities self-regulate their exocellular electron transfer pathways to adapt to different anode potentials.
Collapse
Affiliation(s)
- Xiuping Zhu
- Department of Civil and Environmental Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | | | | | | | | | | |
Collapse
|
18
|
Geothrix fermentans secretes two different redox-active compounds to utilize electron acceptors across a wide range of redox potentials. Appl Environ Microbiol 2012; 78:6987-95. [PMID: 22843516 DOI: 10.1128/aem.01460-12] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The current understanding of dissimilatory metal reduction is based primarily on isolates from the proteobacterial genera Geobacter and Shewanella. However, environments undergoing active Fe(III) reduction often harbor less-well-studied phyla that are equally abundant. In this work, electrochemical techniques were used to analyze respiratory electron transfer by the only known Fe(III)-reducing representative of the Acidobacteria, Geothrix fermentans. In contrast to previously characterized metal-reducing bacteria, which typically reach maximal rates of respiration at electron acceptor potentials of 0 V versus standard hydrogen electrode (SHE), G. fermentans required potentials as high as 0.55 V to respire at its maximum rate. In addition, G. fermentans secreted two different soluble redox-active electron shuttles with separate redox potentials (-0.2 V and 0.3 V). The compound with the lower midpoint potential, responsible for 20 to 30% of electron transfer activity, was riboflavin. The behavior of the higher-potential compound was consistent with hydrophilic UV-fluorescent molecules previously found in G. fermentans supernatants. Both electron shuttles were also produced when cultures were grown with Fe(III), but not when fumarate was the electron acceptor. This study reveals that Geothrix is able to take advantage of higher-redox-potential environments, demonstrates that secretion of flavin-based shuttles is not confined to Shewanella, and points to the existence of high-potential-redox-active compounds involved in extracellular electron transfer. Based on differences between the respiratory strategies of Geothrix and Geobacter, these two groups of bacteria could exist in distinctive environmental niches defined by redox potential.
Collapse
|
19
|
MacDonald LH, Moon HS, Jaffé PR. The role of biomass, electron shuttles, and ferrous iron in the kinetics of Geobacter sulfurreducens-mediated ferrihydrite reduction. WATER RESEARCH 2011; 45:1049-1062. [PMID: 21111440 DOI: 10.1016/j.watres.2010.10.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Revised: 09/29/2010] [Accepted: 10/14/2010] [Indexed: 05/30/2023]
Abstract
This work presents a new framework for describing biologically mediated reduction of thin layers of poorly crystalline iron oxides. The research here explores the nature of the biomass to surface area relationship and the role of biogenic ferrous iron during Geobacter sulfurreducens-mediated ferrihydrite reduction, with and without an electron shuttle, through experiments and a mathematical model. The results indicate that a saturating function of biomass most accurately describes the rate of iron reduction without electron shuttles, based on the principle of electron transfer via direct contact. This study also finds that the most appropriate model of iron reduction in the presence of electron shuttles includes both a saturating function of biomass for electron transfer via direct contact and a first-order electron transfer to ferrihydrite via the electron shuttle, strongly supporting the idea that G. sulfurreducens uses both pathways simultaneously. In all experiments, G. sulfurreducens reduced less than 60% of the total ferric iron, a phenomenon that has often been explained through the inhibitory effects of biogenic ferrous iron in the dissolved phase. However, through experiments with spikes of ferrous sulfate, this study suggests that the role of dissolved ferrous iron is passive in this case, and does not directly inhibit the extent of iron reduction in ferrihydrite coated sand. These experiments find that solid phase ferrous iron is the most probable primary product of ferrihydrite reduction, and that the conversion of solid ferric iron to solid ferrous iron depletes a fixed pool of bioavailable ferric iron, thereby accounting for the incomplete reduction of ferric iron observed here. This is the first reported model that explicitly treats solid ferrous iron as the primary product of reduction, with aqueous ferrous iron as a passive byproduct. This simple mathematical model readily translates to other systems of microbially mediated iron reduction.
Collapse
Affiliation(s)
- Luke H MacDonald
- Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08544, USA
| | | | | |
Collapse
|
20
|
de Cárcer DA, Ha PT, Jang JK, Chang IS. Microbial community differences between propionate-fed microbial fuel cell systems under open and closed circuit conditions. Appl Microbiol Biotechnol 2010; 89:605-12. [DOI: 10.1007/s00253-010-2903-x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Revised: 09/20/2010] [Accepted: 09/20/2010] [Indexed: 10/19/2022]
|
21
|
Heimann A, Jakobsen R, Blodau C. Energetic constraints on H2-dependent terminal electron accepting processes in anoxic environments: a review of observations and model approaches. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010; 44:24-33. [PMID: 20039730 DOI: 10.1021/es9018207] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Microbially mediated terminal electron accepting processes (TEAPs) to a large extent control the fate of redox reactive elements and associated reactions in anoxic soils, sediments, and aquifers. This review focuses on thermodynamic controls and regulation of H2-dependent TEAPs, case studies illustrating this concept, and the quantitative description of thermodynamic controls in modeling. Other electron transfer processes are considered where appropriate. The work reviewed shows that thermodynamics and microbial kinetics are connected near thermodynamic equilibrium. Free energy thresholds for terminal respiration are physiologically based and often near -20 kJ mol(-1), depending on the mechanism of ATP generation; more positive free energy values have been reported under "starvation conditions" for methanogenesis and lower values for TEAPs that provide more energy. H2-dependent methanogenesis and sulfate reduction are under direct thermodynamic control in soils and sediments and generally approach theoretical minimum energy thresholds. If H2 concentrations are lowered by thermodynamically more potent TEAPs, these processes are inhibited. This principle is also valid for TEAPS providing more free energy, such as denitrification and arsenate reduction, but electron donor concentration cannot be lowered so that the processes reach theoretical energy thresholds. Thermodynamics and kinetics have been integrated by combining traditional descriptions of microbial kinetics with the equilibrium constant K and reaction quotient Q of a process, taking into account process-specific threshold energies. This approach is dynamically evolving toward a general concept of microbially driven electron transfer in anoxic environments and has been used successfully in applications ranging from bioreactor regulation to groundwater and sediment biogeochemistry.
Collapse
Affiliation(s)
- Axel Heimann
- Institute of Environment and Resources, Bygningstorvet, Bilding 115, Technical University of Denmark, DK-2800 Lyngby, Denmark
| | | | | |
Collapse
|
22
|
Chapelle FH, Bradley PM, Thomas MA, McMahon PB. Distinguishing iron-reducing from sulfate-reducing conditions. GROUND WATER 2009; 47:300-5. [PMID: 19191885 DOI: 10.1111/j.1745-6584.2008.00536.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/15/2023]
Abstract
Ground water systems dominated by iron- or sulfate-reducing conditions may be distinguished by observing concentrations of dissolved iron (Fe(2+)) and sulfide (sum of H(2)S, HS(-), and S(=) species and denoted here as "H(2)S"). This approach is based on the observation that concentrations of Fe(2+) and H(2)S in ground water systems tend to be inversely related according to a hyperbolic function. That is, when Fe(2+) concentrations are high, H(2)S concentrations tend to be low and vice versa. This relation partly reflects the rapid reaction kinetics of Fe(2+) with H(2)S to produce relatively insoluble ferrous sulfides (FeS). This relation also reflects competition for organic substrates between the iron- and the sulfate-reducing microorganisms that catalyze the production of Fe(2+) and H(2)S. These solubility and microbial constraints operate in tandem, resulting in the observed hyperbolic relation between Fe(2+) and H(2)S concentrations. Concentrations of redox indicators, including dissolved hydrogen (H(2)) measured in a shallow aquifer in Hanahan, South Carolina, suggest that if the Fe(2+)/H(2)S mass ratio (units of mg/L) exceeded 10, the screened interval being tapped was consistently iron reducing (H(2) approximately 0.2 to 0.8 nM). Conversely, if the Fe(2+)/H(2)S ratio was less than 0.30, consistent sulfate-reducing (H(2) approximately 1 to 5 nM) conditions were observed over time. Concomitantly high Fe(2+) and H(2)S concentrations were associated with H(2) concentrations that varied between 0.2 and 5.0 nM over time, suggesting mixing of water from adjacent iron- and sulfate-reducing zones or concomitant iron and sulfate reduction under nonelectron donor-limited conditions. These observations suggest that Fe(2+)/H(2)S mass ratios may provide useful information concerning the occurrence and distribution of iron and sulfate reduction in ground water systems.
Collapse
Affiliation(s)
- Francis H Chapelle
- U.S. Geological Survey, South Carolina Water Science Center, Columbia, SC 29210, USA.
| | | | | | | |
Collapse
|
23
|
Harris SH, Smith RL, Suflita JM. In situ hydrogen consumption kinetics as an indicator of subsurface microbial activity. FEMS Microbiol Ecol 2007; 60:220-8. [PMID: 17439588 DOI: 10.1111/j.1574-6941.2007.00286.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
There are few methods available for broadly assessing microbial community metabolism directly within a groundwater environment. In this study, hydrogen consumption rates were estimated from in situ injection/withdrawal tests conducted in two geochemically varying, contaminated aquifers as an approach towards developing such a method. The hydrogen consumption first-order rates varied from 0.002 nM h(-1) for an uncontaminated, aerobic site to 2.5 nM h(-1) for a contaminated site where sulfate reduction was a predominant process. The method could accommodate the over three orders of magnitude range in rates that existed between subsurface sites. In a denitrifying zone, the hydrogen consumption rate (0.02 nM h(-1)) was immediately abolished in the presence of air or an antibiotic mixture, suggesting that such measurements may also be sensitive to the effects of environmental perturbations on field microbial activities. Comparable laboratory determinations with sediment slurries exhibited hydrogen consumption kinetics that differed substantially from the field estimates. Because anaerobic degradation of organic matter relies on the rapid consumption of hydrogen and subsequent maintenance at low levels, such in situ measures of hydrogen turnover can serve as a key indicator of the functioning of microbial food webs and may be more reliable than laboratory determinations.
Collapse
Affiliation(s)
- Steve H Harris
- Department of Botany and Microbiology, Institute for Energy and the Environment, The University of Oklahoma, Norman, OK, USA.
| | | | | |
Collapse
|
24
|
Karadagli F, Rittmann BE. A mathematical model for the kinetics of Methanobacterium bryantii M.o.H. considering hydrogen thresholds. Biodegradation 2006; 18:453-64. [PMID: 17096208 DOI: 10.1007/s10532-006-9078-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Accepted: 08/08/2006] [Indexed: 11/26/2022]
Abstract
We develop a kinetic model that builds on the foundation of classic Monod kinetics, but incorporates new phenomena such as substrate thresholds and survival mode observed in experiments with the H2-oxidizing methanogen Methanobacterium bryantii M.o.H. We apply our model to the experimental data presented in our companion paper on H2 thresholds. The model accurately describes H2 consumption, CH4 generation, biomass growth, substrate thresholds, and survival state during batch experiments. Methane formation stops when its Gibbs free energy is equal zero, although this does not interrupt H2 oxidation. The thermodynamic threshold for H2 oxidation occurs when the free energy for oxidizing H2 and transferring electrons to biomass is no longer negative, at approximately 0.4 nM. This threshold is not controlled by the Gibbs free energy equation of methanogenesis from H2 + HCO3- as we show in our companion paper. Beyond this threshold, the microorganisms shift to a low-maintenance metabolism called "the survival state" in response to extended H2 starvation; adding the starvation response as another new feature of the kinetic model. A kinetic threshold (or S (min)), a natural feature of the Monod kinetics, is also captured by the model at H2 concentration of around approximately 2,400 nM. S (min) is the minimum substrate concentration to maintain steady-state biomass concentration. Our model will be useful for interpreting threshold results and designing new studies to understand thresholds and their ecological implications.
Collapse
Affiliation(s)
- Fatih Karadagli
- Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA.
| | | |
Collapse
|
25
|
Karadagli F, Rittmann BE. Thermodynamic and kinetic analysis of the H2 threshold for Methanobacterium bryantii M.o.H. Biodegradation 2006; 18:439-52. [PMID: 17091351 DOI: 10.1007/s10532-006-9073-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Accepted: 07/25/2006] [Indexed: 10/23/2022]
Abstract
H2 thresholds, concentrations below which H2 consumption by a microbial group stops, have been associated with microbial respiratory processes such as dechlorination, denitrification, sulfate reduction, and methanogenesis. Researchers have proposed that observed H2 thresholds occur when the available Gibbs free energy is minimal (DeltaG approximately 0) for a specific respiratory reaction. Others suggest that microbial kinetics also may play a role in controlling the thresholds. Here, we comprehensively evaluate H2 thresholds in light of microbial thermodynamic and kinetic principles. We show that a thermodynamic H2 threshold for Methanobacterium bryantii M.o.H. is not controlled by DeltaG for methane production from H2 + HCO3-. We repeatedly attain a H2 threshold near 0.4 nM, with a range of 0.2-1 nM, and DeltaG for methanogenesis from H2 + HCO3- is positive, +5 to +7 kJ/mol-H2, at the threshold in most cases. We postulate that the H2 threshold is controlled by a separate reaction other than methane production. The electrons from H2 oxidation are transferred to an electron sink that is a solid-phase component of the cells. We also show that a kinetic threshold (S(min)) occurs at a theoretically computed H2 concentration of about 2400 nM at which biomass growth shifts from positive to negative.
Collapse
Affiliation(s)
- Fatih Karadagli
- Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3109, USA.
| | | |
Collapse
|