Many iron (Fe) redox processes that were previously assumed to be purely abiotic, such as photochemical Fe reactions, are now known to also be microbially mediated. Owing to this overlap, discerning ...whether biotic or abiotic processes control Fe redox chemistry is a major challenge for geomicrobiologists and biogeochemists alike. Therefore, to understand the network of reactions within the biogeochemical Fe cycle, it is necessary to determine which abiotic or microbially mediated reactions are dominant under various environmental conditions. In this Review, we discuss the major microbially mediated and abiotic reactions in the biogeochemical Fe cycle and provide an integrated overview of biotic and chemically mediated redox transformations.
A fundamental challenge in human missions to Mars is producing consumable foods efficiently with the in situ resources such as soil, water, nutrients and solar radiation available on Mars. The low ...nutrient content of martian soil and high salinity of water render them unfit for direct use for propagating food crops on Mars. It is therefore essential to develop strategies to enhance nutrient content in Mars soil and to desalinate briny water for long-term missions on Mars. We report simple and efficient strategies for treating basaltic regolith simulant soil and briny water simulant for suitable resources for growing plants. We show that alfalfa plants grow well in a nutrient-limited basaltic regolith simulant soil and that the alfalfa biomass can be used as a biofertilizer to sustain growth and production of turnip, radish and lettuce in the basaltic regolith simulant soil. Moreover, we show that marine cyanobacterium Synechococcus sp. PCC 7002 effectively desalinates the briny water simulant, and that desalination can be further enhanced by filtration through basalt-type volcanic rocks. Our findings indicate that it is possible to grow food crops with alfalfa treated basaltic regolith martian soil as a substratum watered with biodesalinated water.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The use of the phenoxy herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) has been steadily increasing in recent years due to its selectivity against broad‐leafed weeds and use on genetically ...modified crops resistant to 2,4‐D. This increases the likelihood of 2,4‐D persisting in agriculturally impacted soils, sediments, and aquatic systems. Aerobic microorganisms are capable of degrading 2,4‐D enzymatically. Anaerobic degradation also occurs, though the enzymatic pathway is unclear. Iron‐reducing bacteria (FeRB) have been hypothesized to augment anaerobic degradation through the production of a chemically reactive Fe(II) adsorbed to Fe(III) oxyhydroxides. To test whether this iron species can catalyze abiotic degradation of 2,4‐D, an enrichment culture (BLA1) containing a photosynthetic Fe(II)‐oxidizing bacterium (FeOB) "
Candidatus
Chlorobium masyuteum" and the FeRB "
Candidatus
Pseudopelobacter ferreus", both of which lacked known 2,4‐D degradation genes was investigated. BLA1 produces Fe(II)‐adsorbed to Fe(III) oxyhydroxides during alternating photoautotrophic iron oxidation and dark iron reduction (amended with acetate) cycles. No 2,4‐D degradation occurred during iron oxidation by FeOB
Ca
. C. masyuteum or during iron reduction by FeRB
Ca
. P. ferreus under any incubation conditions tested (i.e., +/−Fe(II), +/−cells, and +/−light), or due to the presence of Fe(II) adsorbed to Fe(III) oxyhydroxides. Our results cast doubt on the hypothesis that the mineral‐bound Fe(II) species augments the anaerobic degradation of 2,4‐D in anoxic soils and waters by iron‐cycling bacteria, and further justify the need to identify the genetic underpinnings of anaerobic 2,4‐D degradation.
Core Ideas
2,4‐D use has steadily increased due to genetically modified crops.
Biological and chemical degradation pathways are not well understood in anaerobic organisms.
An Fe‐oxidizing and Fe‐reducing bacterial co‐culture did not degrade 2,4‐D in biotic or abiotic 2,4‐D degradation.
No chemical degradation of 2,4‐D by Fe during microbial Fe‐cycling was detected in co‐culture experiments.
Microaerophilic Fe(II)-oxidizing bacteria are often chemolithoautotrophs, and the Fe(III) (oxyhydr)oxides they form could immobilize arsenic (As). If such microbes are active in karstic paddy ...soils, their activity would help increase soil organic carbon and mitigate As contamination. We therefore used gel-stabilized gradient systems to cultivate microaerophilic Fe(II)-oxidizing bacteria from karstic paddy soil to investigate their capacity for Fe(II) oxidation, carbon fixation, and As sequestration. Stable isotope probing demonstrated the assimilation of inorganic carbon at a maximum rate of 8.02 mmol C m–2 d–1. Sequencing revealed that Bradyrhizobium, Cupriavidus, Hyphomicrobium, Kaistobacter, Mesorhizobium, Rhizobium, unclassified Phycisphaerales, and unclassified Opitutaceas were fixing carbon. Fe(II) oxidation produced Fe(III) (oxyhydr)oxides, which can absorb and/or coprecipitate As. Adding As(III) decreased the diversity of functional bacteria involved in carbon fixation, the relative abundance of predicted carbon fixation genes, and the amount of carbon fixed. Although the rate of Fe(II) oxidation was also lower in the presence of As(III), over 90% of the As(III) was sequestered after oxidation. The potential for microbially mediated As(III) oxidation was revealed by the presence of arsenite oxidase gene (aioA), denoting the potential of the Fe(II)-oxidizing and autotrophic microbial community to also oxidize As(III). Thisstudy demonstrates that carbon fixation coupled to Fe(II) oxidation can increase the carbon content in soils by microaerophilic Fe(II)-oxidizing bacteria, as well as accelerate As(III) oxidation and sequester it in association with Fe(III) (oxyhydr)oxides.
Anoxygenic phototrophic Fe(II)-oxidizing bacteria potentially contributed to the deposition of Archean banded iron formations (BIFs), before the evolution of cyanobacterially-generated molecular ...oxygen (O2), by using sunlight to oxidize aqueous Fe(II) and precipitate Fe(III) (oxyhydr)oxides. Once deposited at the seafloor, diagenetic reduction of the Fe(III) (oxyhydr)oxides by heterotrophic bacteria produced secondary Fe(II)-bearing minerals, such as siderite (FeCO3) and magnetite (Fe3O4), via the oxidation of microbial organic carbon (i.e., cellular biomass). During deeper burial at temperatures above the threshold for life, thermochemical Fe(III) reduction has the potential to form BIF-like minerals. However, the role of thermochemical Fe(III) reduction of primary BIF minerals during metamorphism, and its impact on mineralogy and geochemical signatures in BIFs, is poorly understood. Consequently, we simulated the metamorphism of the precursor and diagenetic iron-rich minerals (ferrihydrite, goethite, hematite) at low-grade metamorphic conditions (170 °C, 1.2 kbar) for 14 days by using (1) mixtures of abiotically synthesized Fe(III) minerals and either microbial biomass or glucose as a proxy for biomass, and (2) using biogenic minerals formed by phototrophic Fe(II)-oxidizing bacteria. Mössbauer spectroscopy and μXRD showed that thermochemical magnetite formation was limited to samples containing ferrihydrite and glucose, or goethite and glucose. No magnetite was formed from Fe(III) minerals when microbial biomass was present as the carbon and electron sources for thermochemical Fe(III) reduction. This could be due to biomass-derived organic molecules binding to the mineral surfaces and preventing solid-state conversion to magnetite. Mössbauer spectroscopy revealed siderite contents of up to 17% after only 14 days of incubation at elevated temperature and pressure for all samples with synthetic Fe(III) minerals and biomass, whereas 6% of the initial Fe(III) was reduced to sideritic Fe(II) in biogenic Fe(III) minerals during incubation. Based on our data, magnetite in BIF is unlikely to be formed by thermochemical Fe(III) reduction in sediments of biogenic ferrihydrite, hematite or goethite-dominated sediments with complex microbial biomass present. Instead, our results suggest that diagenetic magnetite in BIF was either formed by microbial Fe(III) reduction during early diagenesis, i.e., below 120 °C, or by thermochemical Fe(III) reduction with simple organic compounds at higher temperatures, whereas siderite was formed by both microbial, diagenetic Fe(III) reduction and thermogenic Fe(III) reduction with complex biomass. Thermochemical Fe(III) reduction coupled to biomass oxidation during metamorphism provides another origin for BIF siderites and could have led to a significant increase in Fe(II) content in BIF after deposition over geological timescales.
•Thermochemical Fe(III) reduction by microbial biomass led to siderite formation.•Thermochemical magnetite formation during BIF low-grade metamorphism is unlikely.•Silica preserved primary ferrihydrite against transformation to hematite.•The presence of silica led to higher Fe(III) reduction yields.•Silica did not influence the final mineralogy during simulated BIF metamorphism.
Anoxic and iron-rich (ferruginous) conditions prevailed in the ocean under the low-oxygen atmosphere that occurred through most of the Archean Eon. While euxinic conditions (i.e. anoxic and hydrogen ...sulfide-rich waters) became more common in the Proterozoic, ferruginous conditions persisted in deep waters. Ferruginous ocean regions would have been a major biosphere and Earth surface reservoir through which elements passed through as part of their global biogeochemical cycles. Understanding key biological events, such as the rise of oxygen in the atmosphere, or even the transitions from ferruginous to euxinic or oxic conditions, requires understanding the biogeochemical processes occurring within ferruginous oceans, and their indicators in the rock record. Important analogs for transitions between ferruginous and oxic or euxinic conditions are paleoferruginous lakes; their sediments commonly host siderite and Ca-carbonates, which are important Precambrian records of the carbon cycling. Lakes that were ferruginous in the past, or euxinic lakes with cryptic iron cycling may also help understand transitions between ferruginous and euxinic conditions in shallow and mid-depth oceanic waters during the Proterozoic. Modern ferruginous meromictic lakes, which host diverse anaerobic microbial communities, are increasingly utilized as biogeochemical analogues for ancient ferruginous oceans. Such lakes are believed to be rare, but regional and geological factors indicate they may be more common than previously thought. While physical mixing processes in lakes and oceans are notably different, many chemical and biological processes are similar. The diversity of sizes, stratifications, and water chemistries in ferruginous lakes thus can be leveraged to explore biogeochemical controls in a range of marine systems: near-shore, off-shore, silled basins, or those dominated by terrestrial or hydrothermal element sources. Ferruginous systems, both extant and extinct, lacustrine and marine, host a continuum of biogeochemical processes that highlight the important role of iron in the evolution of Earth’s surface environment.
•Precambrian marine sediments indicate frequent ferruginous conditions with euxinic intervals.•Siderite from ferruginous lakes informs formation pathways in ferruginous oceans.•Ferruginous meromictic lakes are an expected feature of postglacial landscapes.•Ferruginous lakes can be biogeochemical analogues of ferruginous oceans.
As iron sulfide mineral phases are important sedimentary sinks for naturally occurring or contaminant metals, it is important to know the fate of metals during the diagenetic transformation of ...primary sulfide minerals into more stable phases, such as pyrite (FeS2). Furthermore, the trace metal content of pyrite has been proposed as a marine paleoredox proxy. Given the diverse low-temperature diagenetic formation pathways for pyrite, this use of pyrite requires validation. We, therefore, studied nickel (Ni) and cobalt (Co) incorporation into freshly precipitated mackinawite (FeSm), and after experimental diagenesis to pyrite (FeS2) using S0 as an oxidant at 65 °C. Metal incorporation was quantified on bulk digests using ICP-OES or ICP-AES. Bulk mineralogy was characterized with micro-X-ray diffraction (micro-XRD), documenting the transformation of mackinawite to pyrite. Epoxy grain mounts were made anoxically of mackinawite and pyrite grains. We used synchrotron-based micro-X-ray fluorescence (µXRF) to map the distribution of Co and Ni, as well as to collect multiple energy maps throughout the sulfur (S) K-edge. Iron (Fe) and S K-edge micro-X-ray absorption near edge spectroscopy (µXANES) was used to identify the oxidation state and mineralogy within the experimentally synthesized and diagenetically transformed minerals, and map end-member solid phases within the grain mounts using the multiple energy maps. Metal-free FeSm transformed to pyrite, with residual FeSm detectable. Co- and Ni-containing FeSm also transformed to pyrite, but with multiple techniques detecting FeSm as well as S0, implying less complete transformation to pyrite as compared to metal-free FeSm. These results indicate that Co and Ni may inhibit transformation for FeSm to pyrite, or slow it down. Cobalt concentrations in the solid diminished by 30% during pyrite transformation, indicating that pyrite Co may be a conservative tracer of seawater or porewater Co concentrations. Nickel concentrations increased several-fold after pyrite formation, suggesting that pyrite may have scavenged Ni from the dissolution of primary FeSm grains. Nickel in pyrites thus may not be a reliable proxy for seawater or porewater metal concentrations.
Cyanobacterial harmful algal blooms (CyanoHABs) pose serious risks to inland water resources. Despite advancements in our understanding of associated environmental factors and modeling efforts, ...predicting CyanoHABs remains challenging. Leveraging an integrated water quality data collection effort in Iowa lakes, this study aimed to identify factors associated with hazardous microcystin levels and develop one-week-ahead predictive classification models. Using water samples from 38 Iowa lakes collected between 2018 and 2021, feature selection was conducted considering both linear and nonlinear properties. Subsequently, we developed three model types (Neural Network, XGBoost, and Logistic Regression) with different sampling strategies using the nine selected variables (mcyA_M, TKN, % hay/pasture, pH, mcyA_M:16S, % developed, DOC, dewpoint temperature, and ortho-P). Evaluation metrics demonstrated the strong performance of the Neural Network with oversampling (ROC-AUC 0.940, accuracy 0.861, sensitivity 0.857, specificity 0.857, LR+ 5.993, and 1/LR– 5.993), as well as the XGBoost with downsampling (ROC-AUC 0.944, accuracy 0.831, sensitivity 0.928, specificity 0.833, LR+ 5.557, and 1/LR– 11.569). This study exhibited the intricacies of modeling with limited data and class imbalances, underscoring the importance of continuous monitoring and data collection to improve predictive accuracy. Also, the methodologies employed can serve as meaningful references for researchers tackling similar challenges in diverse environments.
Post-depositional diagenetic alteration makes the accurate interpretation of key precipitation processes in ancient sediments, such as Precambrian banded iron formations (BIFs), difficult. While ...microorganisms are proposed as key contributors to BIF deposition, the diagenetic transformation of precursor Fe(III) minerals associated with microbial biomass had not been experimentally tested. We incubated mixtures of ferrihydrite (proxy for biogenic ferric oxyhydroxide minerals) and glucose (proxy for microbial biomass) in gold capsules at 1.2kbar and 170°C. Both wet chemical analysis and mineralogical methods (microscopy, X-ray diffraction and Mössbauer spectroscopy) were used to analyze the reaction products. Under these conditions, ferrihydrite (FeIII(OH)3) transforms to hematite (Fe2IIIO3), magnetite (FeIIFe2IIIO4), and siderite (FeIICO3). Silica-coated ferrihydrite prepared at conservative Si:Fe ratios (as predicted for the Precambrian oceans) and mixed with glucose yielded hematite and siderite, whereas magnetite could not be identified microscopically. Our results show that electron transfer from organic carbon to Fe(III) minerals during temperature/pressure diagenesis can drive the production of key BIF minerals. Our results also demonstrate that the post-depositional mineralogy of BIF does not directly archive the oceanic or atmospheric conditions present on Earth during their lithification. As a consequence, atmospheric composition regarding concentrations of methane and CO2 during the time of BIF mineral deposition cannot be directly inferred from BIF mineralogical data alone.
•Magnetite, hematite and siderite are found in banded iron formations (BIFs).•Ferrihydrite and glucose diagenesis yields magnetite, hematite and siderite.•Ferrihydrite and glucose mixture is a simple cell–Fe mineral aggregate proxy.•The joint deposition of biomass with Fe(III) oxyhydroxides may have formed BIF.•BIF deposition was decoupled from oceanic or atmospheric conditions.
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