Biogeochemical cycling of iron: Implications for biocementation and slope stabilisation

Rintoul

et al. 2020

Sci Rep

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Robust methods for the characterisation of microbial biosignatures in geological matrices is critical for developing mineralogical biosignatures. Studying microbial fossils is fundamental for our understanding of the role microorganisms have played in elemental cycling in modern and ancient environments on Earth and potentially Mars. Here, we aim to understand what promotes the fossilisation of microorganisms after the initial stages of biomineralisation, committing bacteriomorphic structures to the geological record within iron-rich environments. Mineral encrusted cell envelope structures were routinely identified within a goethite-rich vein that cross-cut the saprolite (iron ore) of a weathered banded iron formation (BIF) system in the Quadrilátero Ferrífero, Brazil. The preservation of potential organic and mineralogical biosignatures associated with these fossils was characterised using the following high-resolution analytical techniques: scanning and transmission electron microscopy, focused ion beam scanning electron microscopy, nanoscale secondary ion mass spectrometry, synchrotron-based Fourier transform infrared spectroscopy and Raman spectroscopy. Electron microscopy demonstrated that mineral nucleation associated with a range of cell envelope structures typically followed the extant cell templates. These biologically-influenced iron-rich minerals are microcrystalline with minimal secondary growth. In contrast, intracellular mineralisation formed larger minerals that grew inward from the cell membrane to infill intracellular voids after cell death. A three dimensional reconstruction of encrusted cell envelopes in a fossilised biofilm suggests that microorganisms may be able to replicate, during the initial stages of mineralisation. Carbon and nitrogen signatures are preserved associated with the cell envelope structures; however, there were no conclusive mineralogical biosignatures associated with the mineralised cell envelopes highlighting the classical importance of morphology and elemental biosignatures in determining the biogenicity of bacteriomorphic structures.

Section: Discussionmentioning

confidence: 99%

Characterisation of iron oxide encrusted microbial fossils

Rintoul

et al. 2020

Sci Rep

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“…Iron reduction is the rate‐limiting step in the natural biogeochemical cycling of iron in canga (Levett et al ., 2020b) and is controlled by the availability of electron donors (carbon or hydrogen) and the presence of anaerobic conditions for microbial respiration to electron acceptors other than oxygen (Gagen et al ., 2018). Providing an easily metabolizable carbon source facilitated the rapid development of anaerobic conditions in our experiment, confirmed by the presence of ferrous iron in pore waters 6 days after reactor construction [if conditions were oxic, at circumneutral pH ferrous iron would have been rapidly oxidized to ferric iron (Hem and Cropper, 1959)].…”

Section: Discussionmentioning

confidence: 99%

“…Cangas are extremely resistant to erosion and represent some of the longest‐lived continuously exposed surfaces on Earth (Monteiro et al ., 2018a). The stability of these kilometre‐scale features is partly the result of repeated biologically mediated dissolution and subsequent reprecipitation of the goethite cements in canga (Monteiro et al ., 2014; Levett et al ., 2020b). If the natural geobiological processes that result in cementation and ‘self‐healing’ of canga over geologic time could be accelerated in the present day, stable iron oxide surface crusts may be re‐formed during the rehabilitation of iron ore mines.…”

Section: Introductionmentioning

confidence: 99%

“…Under circumneutral conditions, the dissolution of crystalline iron oxides (e.g. goethite, hematite) is the rate‐limiting step in the iron cycling necessary for cementation of canga (Monteiro et al ., 2014; Levett et al ., 2020b). We recently enriched a microbial consortium from a canga area, dominated by a novel iron‐reducing Telmatospirillum and capable of significant goethite reduction via sugar fermentation (Gagen et al ., 2019a).…”

Section: Introductionmentioning

confidence: 99%

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Accelerating microbial iron cycling promotes re‐cementation of surface crusts in iron ore regions

Microbial Biotechnology

Paz

et al. 2020

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Accelerating microbial iron cycling is an innovative environmentally responsible strategy for mine remediation. In the present study, we extend the application of microbial iron cycling in environmental remediation, to include biocementation for the aggregation and stabilization of mine wastes. Microbial iron reduction was promoted monthly for 10 months in crushed canga (a by-product from iron ore mining, dominated by crystalline iron oxides) in 1 m 3 containers. Ferrous iron concentrations reached 445 ppm in treatments and diverse lineages of the candidate phyla radiation dominated pore waters, implicating them in fermentation and/or metal cycling in this system. After a 6-month evaporation period, iron-rich cements had formed between grains and 20-cm aggregates were recoverable from treatments throughout the 1-m depth profile, while material from untreated and water-only controls remained unconsolidated. Canga-adapted plants seeded into one of the treatments germinated and grew well. Therefore, application of this geobiotechnology offers promise for stabilization of mine wastes, as well as reformation of surface crusts that underpin unique and threatened plant ecosystems in iron ore regions.

“…The present study aimed to develop a biotechnological approach to canga stabilization for mine remediation. It was, in part, inspired by the microbial communities that contribute to iron cementation in natural duricrusts on the sloped edge of lakes in canga environments (7). New biotechnologies that stabilize canga for iron ore remediation may also be transferable to the stabilization of tailings dams, which are urgently needed given the doubling of dam failures in the last 20 y (8).…”

mentioning

confidence: 99%

Biocement stabilization of an experimental-scale artificial slope and the reformation of iron-rich crusts

Proc. Natl. Acad. Sci. U.S.A.

Zhao

et al. 2020

Self Cite

Novel biotechnologies are required to remediate iron ore mines and address the increasing number of tailings (mine waste) dam collapses worldwide. In this study, we aimed to accelerate iron reduction and oxidation to stabilize an artificial slope. An open-air bioreactor was inoculated with a mixed consortium of microorganisms capable of reducing iron. Fluid from the bioreactor was allowed to overflow onto the artificial slope. Carbon sources from the bioreactor fluid promoted the growth of a surface biofilm within the artificial slope, which naturally aggregated the crushed grains. The biofilms provided an organic framework for the nucleation of iron oxide minerals. Iron-rich biocements stabilized the artificial slope and were significantly more resistant to physical deformation compared with the control experiment. These biotechnologies highlight the potential to develop strategies for mine remediation and waste stabilization by accelerating the biogeochemical cycling of iron.