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Nikeleit V, Roth L, Maisch M, Kappler A, Bryce C. Phototrophic Fe(II) oxidation benefits from light/dark cycles. ENVIRONMENTAL MICROBIOLOGY REPORTS 2024; 16:e13239. [PMID: 38490970 PMCID: PMC10943175 DOI: 10.1111/1758-2229.13239] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Accepted: 02/01/2024] [Indexed: 03/18/2024]
Abstract
Phototrophic Fe(II)-oxidizers use Fe(II) as electron donor for CO2 fixation thus linking Fe(II) oxidation, ATP formation, and growth directly to the availability of sunlight. We compared the effect of short (10 h light/14 h dark) and long (2-3 days light/2-3 days dark) light/dark cycles to constant light conditions for the phototrophic Fe(II)-oxidizer Chlorobium ferrooxidans KoFox. Fe(II) oxidation was completed first in the setup with constant light (9 mM Fe(II) oxidised within 8.9 days) compared to the light/dark cycles but both short and long light/dark cycles showed faster maximum Fe(II) oxidation rates. In the short and long cycle, Fe(II) oxidation rates reached 3.5 ± 1.0 and 2.6 ± 0.3 mM/d, respectively, compared to 2.1 ± 0.3 mM/d in the constant light setup. Maximum Fe(II) oxidation was significantly faster in the short cycle compared to the constant light setup. Cell growth reached roughly equivalent cell numbers across all three light conditions (from 0.2-2.0 × 106 cells/mL to 1.1-1.4 × 108 cells/mL) and took place in both the light and dark phases of incubation. SEM images showed different mineral structures independent of the light setup and 57 Fe Mössbauer spectroscopy confirmed the formation of poorly crystalline Fe(III) oxyhydroxides (such as ferrihydrite) in all three setups. Our results suggest that periods of darkness have a significant impact on phototrophic Fe(II)-oxidizers and significantly influence rates of Fe(II) oxidation.
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Affiliation(s)
- Verena Nikeleit
- Department of GeosciencesUniversity of TübingenTübingenGermany
| | - Linda Roth
- Department of GeosciencesUniversity of TübingenTübingenGermany
| | - Markus Maisch
- Department of GeosciencesUniversity of TübingenTübingenGermany
| | - Andreas Kappler
- Department of GeosciencesUniversity of TübingenTübingenGermany
- Cluster of Excellence: EXC 2124: Controlling Microbes to Fight InfectionsTübingenGermany
| | - Casey Bryce
- School of Earth SciencesUniversity of BristolBristolUK
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PioABC-Dependent Fe(II) Oxidation during Photoheterotrophic Growth on an Oxidized Carbon Substrate Increases Growth Yield. Appl Environ Microbiol 2022; 88:e0097422. [PMID: 35862670 PMCID: PMC9361825 DOI: 10.1128/aem.00974-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Microorganisms that carry out Fe(II) oxidation play a major role in biogeochemical cycling of iron in environments with low oxygen. Fe(II) oxidation has been largely studied in the context of autotrophy. Here, we show that the anoxygenic phototroph, Rhodopseudomonas palustris CGA010, carries out Fe(II) oxidation during photoheterotrophic growth with an oxidized carbon source, malate, leading to an increase in cell yield and allowing more carbon to be directed to cell biomass. We probed the regulatory basis for this by transcriptome sequencing (RNA-seq) and found that the expression levels of the known pioABC Fe(II) oxidation genes in R. palustris depended on the redox-sensing two-component system, RegSR, and the oxidation state of the carbon source provided to cells. This provides the first mechanistic demonstration of mixotrophic growth involving reducing power generated from both Fe(II) oxidation and carbon assimilation. IMPORTANCE The simultaneous use of carbon and reduced metals such as Fe(II) by bacteria is thought to be widespread in aquatic environments, and a mechanistic description of this process could improve our understanding of biogeochemical cycles. Anoxygenic phototrophic bacteria like Rhodopseudomonas palustris typically use light for energy and organic compounds as both a carbon and an electron source. They can also use CO2 for carbon by carbon dioxide fixation when electron-rich compounds like H2, thiosulfate, and Fe(II) are provided as electron donors. Here, we show that Fe(II) oxidation can be used in another context to promote higher growth yields of R. palustris when the oxidized carbon compound malate is provided. We further established the regulatory mechanism underpinning this observation.
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Zhao M, Zhao Y, Lin W, Xiao KQ. An overview of experimental simulations of microbial activity in early Earth. Front Microbiol 2022; 13:1052831. [PMID: 36713221 PMCID: PMC9878457 DOI: 10.3389/fmicb.2022.1052831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Accepted: 12/16/2022] [Indexed: 01/15/2023] Open
Abstract
Microbial activity has shaped the evolution of the ocean and atmosphere throughout the Earth history. Thus, experimental simulations of microbial metabolism under the environment conditions of the early Earth can provide vital information regarding biogeochemical cycles and the interaction and coevolution between life and environment, with important implications for extraterrestrial exploration. In this review, we discuss the current scope and knowledge of experimental simulations of microbial activity in environments representative of those of early Earth, with perspectives on future studies. Inclusive experimental simulations involving multiple species, and cultivation experiments with more constraints on environmental conditions similar to early Earth would significantly advance our understanding of the biogeochemical cycles of the geological past.
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Affiliation(s)
- Mingyu Zhao
- Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
| | - Yao Zhao
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, China
| | - Wei Lin
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
| | - Ke-Qing Xiao
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
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Dreher CL, Schad M, Robbins LJ, Konhauser KO, Kappler A, Joshi P. Microbial processes during deposition and diagenesis of Banded Iron Formations. PALAONTOLOGISCHE ZEITSCHRIFT 2021; 95:593-610. [PMID: 35034981 PMCID: PMC8724090 DOI: 10.1007/s12542-021-00598-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Accepted: 11/22/2021] [Indexed: 06/14/2023]
Abstract
Banded Iron Formations (BIFs) are marine chemical sediments consisting of alternating iron (Fe)-rich and silica (Si)-rich bands which were deposited throughout much of the Precambrian era. BIFs represent important proxies for the geochemical composition of Precambrian seawater and provide evidence for early microbial life. Iron present in BIFs was likely precipitated in the form of Fe3+ (Fe(III)) minerals, such as ferrihydrite (Fe(OH)3), either through the metabolic activity of anoxygenic photoautotrophic Fe2+ (Fe(II))-oxidizing bacteria (photoferrotrophs), by microaerophilic bacteria, or by the oxidation of dissolved Fe(II) by O2 produced by early cyanobacteria. However, in addition to oxidized Fe-bearing minerals such as hematite (FeIII 2O3), (partially) reduced minerals such as magnetite (FeIIFeIII 2O4) and siderite (FeIICO3) are found in BIFs as well. The presence of reduced Fe in BIFs has been suggested to reflect the reduction of primary Fe(III) minerals by dissimilatory Fe(III)-reducing bacteria, or by metamorphic (high pressure and temperature) reactions occurring in presence of buried organic matter. Here, we present the current understanding of the role of Fe-metabolizing bacteria in the deposition of BIFs, as well as competing hypotheses that favor an abiotic model for BIF deposition. We also discuss the potential abiotic and microbial reduction of Fe(III) in BIFs after deposition. Further, we review the availability of essential nutrients (e.g. P and Ni) and their implications on early Earth biogeochemistry. Overall, the combined results of various ancient seawater analogue experiments aimed at assessing microbial iron cycling pathways, coupled with the analysis of the BIF rock record, point towards a strong biotic influence during BIF genesis.
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Affiliation(s)
- Carolin L. Dreher
- Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany
| | - Manuel Schad
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB Canada
| | | | - Kurt O. Konhauser
- Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB Canada
| | - Andreas Kappler
- Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany
| | - Prachi Joshi
- Geomicrobiology, Center for Applied Geosciences, University of Tuebingen, Tuebingen, Germany
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Rego ES, Busigny V, Lalonde SV, Philippot P, Bouyon A, Rossignol C, Babinski M, de Cássia Zapparoli A. Anoxygenic photosynthesis linked to Neoarchean iron formations in Carajás (Brazil). GEOBIOLOGY 2021; 19:326-341. [PMID: 33660904 DOI: 10.1111/gbi.12438] [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: 10/14/2020] [Revised: 02/12/2021] [Accepted: 02/14/2021] [Indexed: 06/12/2023]
Abstract
Microbial activity is often invoked as a direct or indirect contributor to the precipitation of ancient chemical sedimentary rocks such as Precambrian iron formations (IFs). Determining a specific metabolic pathway from the geological record remains a challenge, however, due to a lack of constraints on the initial conditions and microbially induced redox reactions involved in the formation of iron oxides. Thus, there is ongoing debate concerning the role of photoferrotrophy, that is the process by which inorganic carbon is fixed into organic matter using light as an energy source and Fe(II) as an electron donor, in the deposition of IFs. Here, we examine ~2.74-Ga-old Neoarchean IFs and associated carbonates from the Carajás Mineral Province, Brazil, to reconstruct redox conditions and to infer the oxidizing mechanism that allowed one of the world's largest iron deposits to form. The absence of cerium (Ce) anomalies reveals that conditions were pervasively anoxic during IF deposition, while unprecedented europium (Eu) anomalies imply that Fe was supplied by intense hydrothermal activity. A positive and homogeneous Fe isotopic signal in space and time in these IFs indicates a low degree of partial oxidation of Fe(II), which, combined with the presence of 13 C-depleted organic matter, points to a photoautotrophic metabolic driver. Collectively, our results argue in favor of reducing conditions during IF deposition and suggest anoxygenic photosynthesis as the most plausible mechanism responsible for Fe oxidation in the Carajás Basin.
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Affiliation(s)
- Eric Siciliano Rego
- Instituto de Geociências, Universidade de São Paulo, Cidade Universitária, São Paulo, Brazil
- Institut de Physique du Globe de Paris, Université de Paris, CNRS, Paris cedex 05, France
- Géosciences Montpellier, Université de Montpellier, CNRS, Université des Antilles, Montpellier, France
| | - Vincent Busigny
- Institut de Physique du Globe de Paris, Université de Paris, CNRS, Paris cedex 05, France
| | - Stefan V Lalonde
- Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, CNRS, Plouzané, France
| | - Pascal Philippot
- Institut de Physique du Globe de Paris, Université de Paris, CNRS, Paris cedex 05, France
- Géosciences Montpellier, Université de Montpellier, CNRS, Université des Antilles, Montpellier, France
- Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Cidade Universitária, São Paulo, Brazil
| | - Amaury Bouyon
- Géosciences Montpellier, Université de Montpellier, CNRS, Université des Antilles, Montpellier, France
| | - Camille Rossignol
- Institut de Physique du Globe de Paris, Université de Paris, CNRS, Paris cedex 05, France
- Departamento de Geofísica, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Cidade Universitária, São Paulo, Brazil
| | - Marly Babinski
- Instituto de Geociências, Universidade de São Paulo, Cidade Universitária, São Paulo, Brazil
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Tsuji JM, Tran N, Schiff SL, Venkiteswaran JJ, Molot LA, Tank M, Hanada S, Neufeld JD. Anoxygenic photosynthesis and iron-sulfur metabolic potential of Chlorobia populations from seasonally anoxic Boreal Shield lakes. THE ISME JOURNAL 2020; 14:2732-2747. [PMID: 32747714 PMCID: PMC7784702 DOI: 10.1038/s41396-020-0725-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 07/02/2020] [Accepted: 07/20/2020] [Indexed: 12/16/2022]
Abstract
Aquatic environments with high levels of dissolved ferrous iron and low levels of sulfate serve as an important systems for exploring biogeochemical processes relevant to the early Earth. Boreal Shield lakes, which number in the tens of millions globally, commonly develop seasonally anoxic waters that become iron rich and sulfate poor, yet the iron-sulfur microbiology of these systems has been poorly examined. Here we use genome-resolved metagenomics and enrichment cultivation to explore the metabolic diversity and ecology of anoxygenic photosynthesis and iron/sulfur cycling in the anoxic water columns of three Boreal Shield lakes. We recovered four high-completeness and low-contamination draft genome bins assigned to the class Chlorobia (formerly phylum Chlorobi) from environmental metagenome data and enriched two novel sulfide-oxidizing species, also from the Chlorobia. The sequenced genomes of both enriched species, including the novel "Candidatus Chlorobium canadense", encoded the cyc2 gene that is associated with photoferrotrophy among cultured Chlorobia members, along with genes for phototrophic sulfide oxidation. One environmental genome bin also encoded cyc2. Despite the presence of cyc2 in the corresponding draft genome, we were unable to induce photoferrotrophy in "Ca. Chlorobium canadense". Genomic potential for phototrophic sulfide oxidation was more commonly detected than cyc2 among environmental genome bins of Chlorobia, and metagenome and cultivation data suggested the potential for cryptic sulfur cycling to fuel sulfide-based growth. Overall, our results provide an important basis for further probing the functional role of cyc2 and indicate that anoxygenic photoautotrophs in Boreal Shield lakes could have underexplored photophysiology pertinent to understanding Earth's early microbial communities.
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Affiliation(s)
- J M Tsuji
- University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
| | - N Tran
- University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
| | - S L Schiff
- University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
| | - J J Venkiteswaran
- University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
- Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON, N2L 3C5, Canada
| | - L A Molot
- York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada
| | - M Tank
- Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH, Inhoffenstrasse 7B, 38124, Braunschweig, Germany
- Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo, 192-0397, Japan
| | - S Hanada
- Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo, 192-0397, Japan
| | - J D Neufeld
- University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada.
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7
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Zhang J, Qu Y, Qi Q, Zhang P, Zhang Y, Tong YW, He Y. The bio-chemical cycle of iron and the function induced by ZVI addition in anaerobic digestion: A review. WATER RESEARCH 2020; 186:116405. [PMID: 32932096 DOI: 10.1016/j.watres.2020.116405] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2020] [Revised: 08/10/2020] [Accepted: 09/06/2020] [Indexed: 06/11/2023]
Abstract
Zero-valent iron (ZVI) is known to be an additive in facilitating waste treatment and improving biogas production in anaerobic digestion (AD) systems. This review concentrates on the chemical cycle of iron as well as the function of the iron cycle in the removal of four kinds of pollutants: organic carbon, nitrogen, sulphur and phosphorus, which are commonly encountered in waste treatment. In recent studies, the addition of ZVI to an AD system promoted the in-situ production of CH4 from CO2, enabling carbon capture through biotechnology. Additionally, using iron-carbon microbial electrolytic cells in AD systems in order to accelerate electron transport, as well as specific pollutant degradation mechanisms, are illustrated in the present study. Particularly, the main factors affecting the removal efficiency of contaminants in a ZVI-AD system such as pH, VFA/ Alkalinity (ALK), oxidation-reduction potential and particle size are reviewed. According to the above characteristics, combined with technical model and economic analyses, an AD system based on ZVI was considered to be an economical, efficient and carbon-neutral pollutant treatment technology. Accordingly, Iron-based AD is suggested to be a promising and sustainable approach orientated to a circular economy, which may be applied to many waste treatments fields.
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Affiliation(s)
- Jingxin Zhang
- China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai 200240, China.
| | - Yiyuan Qu
- China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Qiuxian Qi
- China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Pengshuai Zhang
- China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Yaobin Zhang
- School of Environmental Science and Technology, Dalian University of Technology, China
| | - Yen Wah Tong
- Department of Chemical & Biomolecular Engineering, National University of Singapore, Singapore
| | - Yiliang He
- China-UK Low Carbon College, Shanghai Jiao Tong University, Shanghai 200240, China; School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
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Bryce C, Blackwell N, Schmidt C, Otte J, Huang YM, Kleindienst S, Tomaszewski E, Schad M, Warter V, Peng C, Byrne JM, Kappler A. Microbial anaerobic Fe(II) oxidation - Ecology, mechanisms and environmental implications. Environ Microbiol 2018; 20:3462-3483. [DOI: 10.1111/1462-2920.14328] [Citation(s) in RCA: 104] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 06/15/2018] [Accepted: 06/16/2018] [Indexed: 11/30/2022]
Affiliation(s)
- Casey Bryce
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | - Nia Blackwell
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | | | - Julia Otte
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | - Yu-Ming Huang
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | | | | | - Manuel Schad
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | - Viola Warter
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | - Chao Peng
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | - James M. Byrne
- Geomicrobiology; University of Tübingen; Tübingen Germany
| | - Andreas Kappler
- Geomicrobiology; University of Tübingen; Tübingen Germany
- Center for Geomicrobiology, Department of Bioscience; Aarhus University; Aarhus Denmark
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Proteome Response of a Metabolically Flexible Anoxygenic Phototroph to Fe(II) Oxidation. Appl Environ Microbiol 2018; 84:AEM.01166-18. [PMID: 29915106 DOI: 10.1128/aem.01166-18] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Accepted: 06/07/2018] [Indexed: 11/20/2022] Open
Abstract
The oxidation of Fe(II) by anoxygenic photosynthetic bacteria was likely a key contributor to Earth's biosphere prior to the evolution of oxygenic photosynthesis and is still found in a diverse range of modern environments. All known phototrophic Fe(II) oxidizers can utilize a wide range of substrates, thus making them very metabolically flexible. However, the underlying adaptations required to oxidize Fe(II), a potential stressor, are not completely understood. We used a combination of quantitative proteomics and cryogenic transmission electron microscopy (cryo-TEM) to compare cells of Rhodopseudomonas palustris TIE-1 grown photoautotrophically with Fe(II) or H2 and photoheterotrophically with acetate. We observed unique proteome profiles for each condition, with differences primarily driven by carbon source. However, these differences were not related to carbon fixation but to growth and light harvesting processes, such as pigment synthesis. Cryo-TEM showed stunted development of photosynthetic membranes in photoautotrophic cultures. Growth on Fe(II) was characterized by a response typical of iron homeostasis, which included an increased abundance of proteins required for metal efflux (particularly copper) and decreased abundance of iron import proteins, including siderophore receptors, with no evidence of further stressors, such as oxidative damage. This study suggests that the main challenge facing anoxygenic phototrophic Fe(II) oxidizers comes from growth limitations imposed by autotrophy, and, once this challenge is overcome, iron stress can be mitigated using iron management mechanisms common to diverse bacteria (e.g., by control of iron influx and efflux).IMPORTANCE The cycling of iron between redox states leads to the precipitation and dissolution of minerals, which can in turn impact other major biogeochemical cycles, such as those of carbon, nitrogen, phosphorus and sulfur. Anoxygenic phototrophs are one of the few drivers of Fe(II) oxidation in anoxic environments and are thought to contribute significantly to iron cycling in both modern and ancient environments. These organisms thrive at high Fe(II) concentrations, yet the adaptations required to tolerate the stresses associated with this are unclear. Despite the general consensus that high Fe(II) concentrations pose numerous stresses on these organisms, our study of the large-scale proteome response of a model anoxygenic phototroph to Fe(II) oxidation demonstrates that common iron homeostasis strategies are adequate to manage this. The bulk of the proteome response is not driven by adaptations to Fe(II) stress but to adaptations required to utilize an inorganic carbon source. Such a global overview of the adaptation of these organisms to Fe(II) oxidation provides valuable insights into the physiology of these biogeochemically important organisms and suggests that Fe(II) oxidation may not pose as many challenges to anoxygenic phototrophs as previously thought.
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Camacho A, Walter XA, Picazo A, Zopfi J. Photoferrotrophy: Remains of an Ancient Photosynthesis in Modern Environments. Front Microbiol 2017; 8:323. [PMID: 28377745 PMCID: PMC5359306 DOI: 10.3389/fmicb.2017.00323] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 02/15/2017] [Indexed: 11/13/2022] Open
Abstract
Photoferrotrophy, the process by which inorganic carbon is fixed into organic matter using light as an energy source and reduced iron [Fe(II)] as an electron donor, has been proposed as one of the oldest photoautotrophic metabolisms on Earth. Under the iron-rich (ferruginous) but sulfide poor conditions dominating the Archean ocean, this type of metabolism could have accounted for most of the primary production in the photic zone. Here we review the current knowledge of biogeochemical, microbial and phylogenetic aspects of photoferrotrophy, and evaluate the ecological significance of this process in ancient and modern environments. From the ferruginous conditions that prevailed during most of the Archean, the ancient ocean evolved toward euxinic (anoxic and sulfide rich) conditions and, finally, much after the advent of oxygenic photosynthesis, to a predominantly oxic environment. Under these new conditions photoferrotrophs lost importance as primary producers, and now photoferrotrophy remains as a vestige of a formerly relevant photosynthetic process. Apart from the geological record and other biogeochemical markers, modern environments resembling the redox conditions of these ancient oceans can offer insights into the past significance of photoferrotrophy and help to explain how this metabolism operated as an important source of organic carbon for the early biosphere. Iron-rich meromictic (permanently stratified) lakes can be considered as modern analogs of the ancient Archean ocean, as they present anoxic ferruginous water columns where light can still be available at the chemocline, thus offering suitable niches for photoferrotrophs. A few bacterial strains of purple bacteria as well as of green sulfur bacteria have been shown to possess photoferrotrophic capacities, and hence, could thrive in these modern Archean ocean analogs. Studies addressing the occurrence and the biogeochemical significance of photoferrotrophy in ferruginous environments have been conducted so far in lakes Matano, Pavin, La Cruz, and the Kabuno Bay of Lake Kivu. To date, only in the latter two lakes a biogeochemical role of photoferrotrophs has been confirmed. In this review we critically summarize the current knowledge on iron-driven photosynthesis, as a remains of ancient Earth biogeochemistry.
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Affiliation(s)
- Antonio Camacho
- Cavanilles Institute for Biodiversity and Evolutionary Biology, University of ValenciaBurjassot, Spain
| | - Xavier A. Walter
- Bristol BioEnergy Centre, Bristol Robotics Laboratory, University of the West of EnglandBristol, UK
| | - Antonio Picazo
- Cavanilles Institute for Biodiversity and Evolutionary Biology, University of ValenciaBurjassot, Spain
| | - Jakob Zopfi
- Aquatic and Stable Isotope Biogeochemistry, Department of Environmental Sciences, University of BaselBasel, Switzerland
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Rantamäki S, Meriluoto J, Spoof L, Puputti EM, Tyystjärvi T, Tyystjärvi E. Oxygen produced by cyanobacteria in simulated Archaean conditions partly oxidizes ferrous iron but mostly escapes-conclusions about early evolution. PHOTOSYNTHESIS RESEARCH 2016; 130:103-111. [PMID: 26895438 DOI: 10.1007/s11120-016-0231-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Accepted: 02/10/2016] [Indexed: 06/05/2023]
Abstract
The Earth has had a permanently oxic atmosphere only since the great oxygenation event (GOE) 2.3-2.4 billion years ago but recent geochemical research has revealed short periods of oxygen in the atmosphere up to a billion years earlier before the permanent oxygenation. If these "whiffs" of oxygen truly occurred, then oxygen-evolving (proto)cyanobacteria must have existed throughout the Archaean aeon. Trapping of oxygen by ferrous iron and other reduced substances present in Archaean oceans has often been suggested to explain why the oxygen content of the atmosphere remained negligible before the GOE although cyanobacteria produced oxygen. We tested this hypothesis by growing cyanobacteria in anaerobic high-CO2 atmosphere in a medium with a high concentration of ferrous iron. Microcystins are known to chelate iron, which prompted us also to test the effects of microcystins and nodularins on iron tolerance. The results show that all tested cyanobacteria, especially nitrogen-fixing species grown in the absence of nitrate, and irrespective of the ability to produce cyanotoxins, were iron sensitive in aerobic conditions but tolerated high concentrations of iron in anaerobicity. This result suggests that current cyanobacteria would have tolerated the high-iron content of Archaean oceans. However, only 1 % of the oxygen produced by the cyanobacterial culture was trapped by iron, suggesting that large-scale cyanobacterial photosynthesis would have oxygenated the atmosphere even if cyanobacteria grew in a reducing ocean. Recent genomic analysis suggesting that ability to colonize seawater is a secondary trait in cyanobacteria may offer a partial explanation for the sustained inefficiency of cyanobacterial photosynthesis during the Archaean aeon, as fresh water has always covered a very small fraction of the Earth's surface. If oxygenic photosynthesis originated in fresh water, then the GOE marks the adaptation of cyanobacteria to seawater, and the late-Proterozoic increase in oxygen concentration of the atmosphere is caused by full oxidation of the oceans.
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Affiliation(s)
- Susanne Rantamäki
- Department of Biochemistry/Molecular Plant Biology, University of Turku, 20014, Turku, Finland
| | - Jussi Meriluoto
- Biochemistry, Faculty of Biosciences, Åbo Akademi University, Tykistökatu 6 A, 20520, Turku, Finland
| | - Lisa Spoof
- Biochemistry, Faculty of Biosciences, Åbo Akademi University, Tykistökatu 6 A, 20520, Turku, Finland
| | - Eeva-Maija Puputti
- Department of Biochemistry/Molecular Plant Biology, University of Turku, 20014, Turku, Finland
| | - Taina Tyystjärvi
- Department of Biochemistry/Molecular Plant Biology, University of Turku, 20014, Turku, Finland
| | - Esa Tyystjärvi
- Department of Biochemistry/Molecular Plant Biology, University of Turku, 20014, Turku, Finland.
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Konhauser KO, Robbins LJ, Pecoits E, Peacock C, Kappler A, Lalonde SV. The Archean Nickel Famine Revisited. ASTROBIOLOGY 2015; 15:804-815. [PMID: 26426143 DOI: 10.1089/ast.2015.1301] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Iron formations (IF) preserve a history of Precambrian oceanic elemental abundance that can be exploited to examine nutrient limitations on early biological productivity. However, in order for IF to be employed as paleomarine proxies, lumped-process distribution coefficients for the element of interest must be experimentally determined or assumed. This necessitates consideration of bulk ocean chemistry and which authigenic ferric iron minerals controlled the sorption reactions. It also requires an assessment of metal mobilization reactions that might have occurred in the water column during particle descent and during post-depositional burial. Here, we summarize recent developments pertaining to the interpretation and fidelity of the IF record in reconstructions of oceanic trace element evolution. Using an updated compilation, we reexamine and validate temporal trends previously reported for the nickel content in IF (see Konhauser et al., 2009 ). Finally, we reevaluate the consequences of methanogen Ni starvation in the context of evolving views of the Archean ocean-climate system and how the Ni famine may have ultimately facilitated the rise in atmospheric oxygen.
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Affiliation(s)
- Kurt O Konhauser
- 1 Department of Earth and Atmospheric Sciences, University of Alberta , Edmonton, Canada
| | - Leslie J Robbins
- 1 Department of Earth and Atmospheric Sciences, University of Alberta , Edmonton, Canada
| | - Ernesto Pecoits
- 1 Department of Earth and Atmospheric Sciences, University of Alberta , Edmonton, Canada
- 2 Equipe Géobiosphère, Institut de Physique du Globe-Sorbonne Paris Cité, Université Paris Diderot , CNRS, Paris, France
| | - Caroline Peacock
- 3 School of Earth and Environment, University of Leeds , Leeds, UK
| | - Andreas Kappler
- 4 Geomicrobiology, Center for Applied Geoscience, Eberhard-Karls-University Tuebingen , Tuebingen, Germany
| | - Stefan V Lalonde
- 5 CNRS-UMR6538 Laboratoire Domaines Océaniques, European Institute for Marine Studies , Technopôle Brest-Iroise, Plouzané, France
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Pecoits E, Smith ML, Catling DC, Philippot P, Kappler A, Konhauser KO. Atmospheric hydrogen peroxide and Eoarchean iron formations. GEOBIOLOGY 2015; 13:1-14. [PMID: 25324177 DOI: 10.1111/gbi.12116] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 09/15/2014] [Indexed: 06/04/2023]
Abstract
It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and the precipitation of iron formations (IF) during the Late Archean-Early Paleoproterozoic (2.7-2.4 Ga). It is less clear whether microbes similarly caused the deposition of the oldest IF at ca. 3.8 Ga, which would imply photosynthesis having already evolved by that time. Abiological alternatives, such as the direct oxidation of dissolved Fe(II) by ultraviolet radiation may have occurred, but its importance has been discounted in environments where the injection of high concentrations of dissolved iron directly into the photic zone led to chemical precipitation reactions that overwhelmed photooxidation rates. However, an outstanding possibility remains with respect to photochemical reactions occurring in the atmosphere that might generate hydrogen peroxide (H2 O2 ), a recognized strong oxidant for ferrous iron. Here, we modeled the amount of H2 O2 that could be produced in an Eoarchean atmosphere using updated solar fluxes and plausible CO2 , O2 , and CH4 mixing ratios. Irrespective of the atmospheric simulations, the upper limit of H2 O2 rainout was calculated to be <10(6) molecules cm(-2) s(-1) . Using conservative Fe(III) sedimentation rates predicted for submarine hydrothermal settings in the Eoarchean, we demonstrate that the flux of H2 O2 was insufficient by several orders of magnitude to account for IF deposition (requiring ~10(11) H2 O2 molecules cm(-2) s(-1) ). This finding further constrains the plausible Fe(II) oxidation mechanisms in Eoarchean seawater, leaving, in our opinion, anoxygenic phototrophic Fe(II)-oxidizing micro-organisms the most likely mechanism responsible for Earth's oldest IF.
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Affiliation(s)
- E Pecoits
- Equipe Géobiosphère, Institut de Physique du Globe-Sorbonne Paris Cité, Université Paris Diderot, CNRS, Paris, France; Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
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Walter XA, Picazo A, Miracle MR, Vicente E, Camacho A, Aragno M, Zopfi J. Phototrophic Fe(II)-oxidation in the chemocline of a ferruginous meromictic lake. Front Microbiol 2014; 5:713. [PMID: 25538702 PMCID: PMC4258642 DOI: 10.3389/fmicb.2014.00713] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Accepted: 11/30/2014] [Indexed: 12/02/2022] Open
Abstract
Precambrian Banded Iron Formation (BIF) deposition was conventionally attributed to the precipitation of iron-oxides resulting from the abiotic reaction of ferrous iron (Fe(II)) with photosynthetically produced oxygen. Earliest traces of oxygen date from 2.7 Ga, thus raising questions as to what may have caused BIF precipitation before oxygenic photosynthesis evolved. The discovery of anoxygenic phototrophic bacteria thriving through the oxidation of Fe(II) has provided support for a biological origin for some BIFs, but despite reports suggesting that anoxygenic phototrophs may oxidize Fe(II) in the environment, a model ecosystem of an ancient ocean where they are demonstrably active was lacking. Here we show that anoxygenic phototrophic bacteria contribute to Fe(II) oxidation in the water column of the ferruginous sulfate-poor, meromictic lake La Cruz (Spain). We observed in-situ photoferrotrophic activity through stimulation of phototrophic carbon uptake in the presence of Fe(II), and determined light-dependent Fe(II)-oxidation by the natural chemocline microbiota. Moreover, a photoferrotrophic bacterium most closely related to Chlorobium ferrooxidans was enriched from the ferruginous water column. Our study for the first time demonstrates a direct link between anoxygenic photoferrotrophy and the anoxic precipitation of Fe(III)-oxides in a ferruginous water column, providing a plausible mechanism for the bacterial origin of BIFs before the advent of free oxygen. However, photoferrotrophs represent only a minor fraction of the anoxygenic phototrophic community with the majority apparently thriving by sulfur cycling, despite the very low sulfur content in the ferruginous chemocline of Lake La Cruz.
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Affiliation(s)
- Xavier A Walter
- Laboratory of Microbiology, Institute of Biology, University of Neuchâtel Neuchâtel, Switzerland ; Faculty of Environment and Technology, Bristol BioEnergy Centre, University of the West of England Bristol, UK
| | - Antonio Picazo
- Department of Microbiology and Ecology, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia Burjassot, Spain
| | - Maria R Miracle
- Department of Microbiology and Ecology, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia Burjassot, Spain
| | - Eduardo Vicente
- Department of Microbiology and Ecology, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia Burjassot, Spain
| | - Antonio Camacho
- Department of Microbiology and Ecology, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia Burjassot, Spain
| | - Michel Aragno
- Laboratory of Microbiology, Institute of Biology, University of Neuchâtel Neuchâtel, Switzerland
| | - Jakob Zopfi
- Laboratory of Microbiology, Institute of Biology, University of Neuchâtel Neuchâtel, Switzerland ; Aquatic and Stable Isotope Biogeochemistry, Department of Environmental Sciences, University of Basel Basel, Switzerland
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Melton ED, Swanner ED, Behrens S, Schmidt C, Kappler A. The interplay of microbially mediated and abiotic reactions in the biogeochemical Fe cycle. Nat Rev Microbiol 2014; 12:797-808. [DOI: 10.1038/nrmicro3347] [Citation(s) in RCA: 503] [Impact Index Per Article: 50.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Biological carbon precursor to diagenetic siderite with spherical structures in iron formations. Nat Commun 2013; 4:1741. [DOI: 10.1038/ncomms2770] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Accepted: 03/19/2013] [Indexed: 11/08/2022] Open
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Bourbin M, Derenne S, Gourier D, Rouzaud JN, Gautret P, Westall F. Electron paramagnetic resonance study of a photosynthetic microbial mat and comparison with Archean cherts. ORIGINS LIFE EVOL B 2012; 42:569-85. [PMID: 23254854 DOI: 10.1007/s11084-012-9320-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Accepted: 11/07/2012] [Indexed: 11/25/2022]
Abstract
Organic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts.
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Affiliation(s)
- M Bourbin
- Biogéochimie et Ecologie des Milieux Continentaux, UMR CNRS 7618, Université Pierre et Marie Curie, 4 place Jussieu, 75252, Paris Cedex 05, France
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Wu W, Li B, Hu J, Li J, Wang F, Pan Y. Iron reduction and magnetite biomineralization mediated by a deep-sea iron-reducing bacteriumShewanella piezotoleransWP3. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jg001728] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Cockell CS, Kelly LC, Summers S, Marteinsson V. Following the kinetics: iron-oxidizing microbial mats in cold icelandic volcanic habitats and their rock-associated carbonaceous signature. ASTROBIOLOGY 2011; 11:679-694. [PMID: 21895443 DOI: 10.1089/ast.2011.0606] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Icelandic streams with mean annual temperatures of less than 5 °C, which receive the cationic products of basaltic rock weathering, were found to host mats of iron-cycling microorganisms. We investigated two representative sites. Iron-oxidizing Gallionella and iron-reducing Geobacter species were present. The mats host a high bacterial diversity as determined by culture-independent methods. β-Proteobacteria, Actinobacteria, α-Proteobacteria, and Bacteroidetes were abundant microbial taxa. The mat contained a high number of phototroph sequences. The carbon compounds in the mat displayed broad G and D bands with Raman spectroscopy. This signature becomes incorporated into the weathered oxidized surface layer of the basaltic rocks and was observed on rocks that no longer host mats. The presence of iron-oxidizing taxa in the stream microbial mats, and the lack of them in previously studied volcanic rocks in Iceland that have intermittently been exposed to surface water flows, can be explained by the kinetic limitations to the extraction of reduced iron from rocks. This type of ecosystem illustrates key factors that control the distribution of chemolithotrophs in cold volcanic environments. The data show that one promising sample type for which the hypothesis of the existence of past life on Mars can be tested is the surface of volcanic rocks that, previously, were situated within channels carved by flowing water. Our results also show that the carbonaceous signatures of life, if life had occurred, could be found in or on these rocks.
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Affiliation(s)
- Charles S Cockell
- Centre for Earth, Planetary, Space and Astronomical Research, Open University, Milton Keynes, UK.
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Cockell CS. Life in the lithosphere, kinetics and the prospects for life elsewhere. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2011; 369:516-537. [PMID: 21220278 DOI: 10.1098/rsta.2010.0232] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The global contiguity of life on the Earth today is a result of the high flux of carbon and oxygen from oxygenic photosynthesis over the planetary surface and its use in aerobic respiration. Life's ability to directly use redox couples from components of the planetary lithosphere in a pre-oxygenic photosynthetic world can be investigated by studying the distribution of organisms that use energy sources normally bound within rocks, such as iron. Microbiological data from Iceland and the deep oceans show the kinetic limitations of living directly off igneous rocks in the lithosphere. Using energy directly extracted from rocks the lithosphere will support about six orders of magnitude less productivity than the present-day Earth, and it would be highly localized. Paradoxically, the biologically extreme conditions of the interior of a planet and the inimical conditions of outer space, between which life is trapped, are the locations from which volcanism and impact events, respectively, originate. These processes facilitate the release of redox couples from the planetary lithosphere and might enable it to achieve planetary-scale productivity approximately one to two orders of magnitude lower than that produced by oxygenic photosynthesis. The significance of the detection of extra-terrestrial life is that it will allow us to test these observations elsewhere and establish an understanding of universal relationships between lithospheres and life. These data also show that the search for extra-terrestrial life must be accomplished by 'following the kinetics', which is different from following the water or energy.
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Affiliation(s)
- Charles S Cockell
- Planetary and Space Sciences Research Institute, The Open University, Milton Keynes MK7 6AA, UK.
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21
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Cockell CS. Vacant habitats in the Universe. Trends Ecol Evol 2011; 26:73-80. [DOI: 10.1016/j.tree.2010.11.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2010] [Revised: 11/13/2010] [Accepted: 11/15/2010] [Indexed: 12/14/2022]
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Chan CS, Fakra SC, Emerson D, Fleming EJ, Edwards KJ. Lithotrophic iron-oxidizing bacteria produce organic stalks to control mineral growth: implications for biosignature formation. ISME JOURNAL 2010; 5:717-27. [PMID: 21107443 DOI: 10.1038/ismej.2010.173] [Citation(s) in RCA: 175] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Neutrophilic Fe-oxidizing bacteria (FeOB) are often identified by their distinctive morphologies, such as the extracellular twisted ribbon-like stalks formed by Gallionella ferruginea or Mariprofundus ferrooxydans. Similar filaments preserved in silica are often identified as FeOB fossils in rocks. Although it is assumed that twisted iron stalks are indicative of FeOB, the stalk's metabolic role has not been established. To this end, we studied the marine FeOB M. ferrooxydans by light, X-ray and electron microscopy. Using time-lapse light microscopy, we observed cells excreting stalks during growth (averaging 2.2 μm h(-1)). Scanning transmission X-ray microscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy show that stalks are Fe(III)-rich, whereas cells are low in Fe. Transmission electron microscopy reveals that stalks are composed of several fibrils, which contain few-nanometer-sized iron oxyhydroxide crystals. Lepidocrocite crystals that nucleated on the fibril surface are much larger (∼100 nm), suggesting that mineral growth within fibrils is retarded, relative to sites surrounding fibrils. C and N 1s NEXAFS spectroscopy and fluorescence probing show that stalks primarily contain carboxyl-rich polysaccharides. On the basis of these results, we suggest a physiological model for Fe oxidation in which cells excrete oxidized Fe bound to organic polymers. These organic molecules retard mineral growth, preventing cell encrustation. This model describes an essential role for stalk formation in FeOB growth. We suggest that stalk-like morphologies observed in modern and ancient samples may be correlated confidently with the Fe-oxidizing metabolism as a robust biosignature.
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Affiliation(s)
- Clara S Chan
- Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA.
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Poulain AJ, Newman DK. Rhodobacter capsulatus catalyzes light-dependent Fe(II) oxidation under anaerobic conditions as a potential detoxification mechanism. Appl Environ Microbiol 2009; 75:6639-46. [PMID: 19717624 PMCID: PMC2772431 DOI: 10.1128/aem.00054-09] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Accepted: 08/22/2009] [Indexed: 11/20/2022] Open
Abstract
Diverse bacteria are known to oxidize millimolar concentrations of ferrous iron [Fe(II)] under anaerobic conditions, both phototrophically and chemotrophically. Yet whether they can do this under conditions that are relevant to natural systems is understood less well. In this study, we tested how light, Fe(II) speciation, pH, and salinity affected the rate of Fe(II) oxidation by Rhodobacter capsulatus SB1003. Although R. capsulatus cannot grow photoautotrophically on Fe(II), it oxidizes Fe(II) at rates comparable to those of bacteria that do grow photoautotrophically on Fe(II) as soon as it is exposed to light, provided it has a functional photosystem. Chelation of Fe(II) by diverse organic ligands promotes Fe(II) oxidation, and as the pH increases, so does the oxidation rate, except in the presence of nitrilotriacetate; nonchelated forms of Fe(II) are also more rapidly oxidized at higher pH. Salt concentrations typical of marine environments inhibit Fe(II) oxidation. When growing photoheterotrophically on humic substances, R. capsulatus is highly sensitive to low concentrations of Fe(II); it is inhibited in the presence of concentrations as low as 5 microM. The product of Fe(II) oxidation, ferric iron, does not hamper growth under these conditions. When other parameters, such as pH or the presence of chelators, are adjusted to promote Fe(II) oxidation, the growth inhibition effect of Fe(II) is alleviated. Together, these results suggest that Fe(II) is toxic to R. capsulatus growing under strictly anaerobic conditions and that Fe(II) oxidation alleviates this toxicity.
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Affiliation(s)
- Alexandre J. Poulain
- Biaology Department, Massachusetts Institute of Technology, 68-380, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Earth, Atmospheric and Planetary Sciences Department, Massachusetts Institute of Technology, 68-380, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Howard Hughes Medical Institute, 68-380, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
| | - Dianne K. Newman
- Biaology Department, Massachusetts Institute of Technology, 68-380, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Earth, Atmospheric and Planetary Sciences Department, Massachusetts Institute of Technology, 68-380, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Howard Hughes Medical Institute, 68-380, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
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