Direct precipitation of siderite in ferruginous environments

Siderite (FeCO3) is often assumed to precipitate from dissimilatory reduction of Fe-(oxyhydr)oxides, but geochemical and mineralogical analyses from ferruginous (anoxic, Fe-rich) Canyon Lake, USA, suggest Fe-carbonate represents a direct early precipitate unrelated to substantial oxide burial. X-ray absorption near edge structure (XANES) spectroscopy of sediment trap materials and an anoxic sediment core indicated a mixture of Fe(II) and Fe(III) in water column particulates and ferruginous surface sediments, while all Mn phases were reduced. About 60 cm below the sediment–water interface, Fe-Mn carbonates were detected by X-ray diffraction and XANES, while Fe extended X-ray absorption fine structure (EXAFS) spectra were best fit with combinations of a biogenic Fe-oxyhydroxide (“Bio Fe”), greigite, and siderite. Sediment Fe speciation indicates a large pool of reduced Fe with a minor component of oxides. Although we found no evidence of significant carbonate phases above or below the 60 cm horizon, equilibrium modelling indicates siderite supersaturation throughout surface sediment porewater, with pH as the primary control on supersaturation. We conclude that delivery of wildfire ash to sediments increased pH, initiating siderite precipitation from ferruginous porewater.This article is published as Grengs, A., G. Ledesma, Y. Xiong, S. Katsev, S. W. Poulton, E. D. Swanner, and C. Wittkop. "Direct precipitation of siderite in ferruginous environments." 30 (2024): 1-6. https://doi.org/10.7185/geochemlet.2414. © 2024 The Authors. Under Creative Commons License CC BY-NC-ND 4.0

Iron Isotope Fractionation during Fe(II) Oxidation Mediated by the Oxygen-Producing Marine Cyanobacterium Synechococcus PCC 7002

In this study, we couple iron isotope analysis to microscopic and mineralogical investigation of iron speciation during circumneutral Fe(II) oxidation and Fe(III) precipitation with photosynthetically produced oxygen. In the presence of the cyanobacterium Synechococcus PCC 7002, aqueous Fe(II) (Fe(II)aq) is oxidized and precipitated as amorphous Fe(III) oxyhydroxide minerals (iron precipitates, Feppt), with distinct isotopic fractionation (ε56Fe) values determined from fitting the δ56Fe(II)aq (1.79‰ and 2.15‰) and the δ56Feppt (2.44‰ and 2.98‰) data trends from two replicate experiments. Additional Fe(II) and Fe(III) phases were detected using microscopy and chemical extractions and likely represent Fe(II) and Fe(III) sorbed to minerals and cells. The iron desorbed with sodium acetate (FeNaAc) yielded heavier δ56Fe compositions than Fe(II)aq. Modeling of the fractionation during Fe(III) sorption to cells and Fe(II) sorption to Feppt, combined with equilibration of sorbed iron and with Fe(II)aq using published fractionation factors, is consistent with our resulting δ56FeNaAc. The δ56Feppt data trend is inconsistent with complete equilibrium exchange with Fe(II)aq. Because of this and our detection of microbially excreted organics (e.g., exopolysaccharides) coating Feppt in our microscopic analysis, we suggest that electron and atom exchange is partially suppressed in this system by biologically produced organics. These results indicate that cyanobacteria influence the fate and composition of iron in sunlit environments via their role in Fe(II) oxidation through O2 production, the capacity of their cell surfaces to sorb iron, and the interaction of secreted organics with Fe(III) minerals

Manganese-Rich Sandstones as an Indicator of Ancient Oxic Lake Water Conditions in Gale Crater, Mars

Manganese has been observed on Mars by the NASA Curiosity rover in a variety of contexts and is an important indicator of redox processes in hydrologic systems on Earth. Within the Murray formation, an ancient primarily fine-grained lacustrine sedimentary deposit in Gale crater, Mars, have observed up to 45× enrichment in manganese and up to 1.5× enrichment in iron within coarser grained bedrock targets compared to the mean Murray sediment composition. This enrichment in manganese coincides with the transition between two stratigraphic units within the Murray: Sutton Island, interpreted as a lake margin environment, and Blunts Point, interpreted as a lake environment. On Earth, lacustrine environments are common locations of manganese precipitation due to highly oxidizing conditions in the lakes. Here, we explore three mechanisms for ferromanganese oxide precipitation at this location: authigenic precipitation from lake water along a lake shore, authigenic precipitation from reduced groundwater discharging through porous sands along a lake shore, and early diagenetic precipitation from groundwater through porous sands. All three scenarios require highly oxidizing conditions and we discuss oxidants that may be responsible for the oxidation and precipitation of manganese oxides. This work has important implications for the habitability of Mars to microbes that could have used Mn redox reactions, owing to its multiple redox states, as an energy source for metabolism.This article is published as Gasda, P. J., Lanza, N. L., Meslin, P.‐Y., Lamm, S. N., Cousin, A., Anderson, R., et al. (2024). Manganese‐rich sandstones as an indicator of ancient oxic lake water conditions in Gale crater, Mars. Journal of Geophysical Research: Planets, 129, e2023JE007923. https://doi.org/10.1029/2023JE007923. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA

Potential for Nitrogen Fixation and Nitrification in the Granite-Hosted Subsurface at Henderson Mine, CO

The existence of life in the deep terrestrial subsurface is established, yet few studies have investigated the origin of nitrogen that supports deep life. Previously, 16S rRNA gene surveys cataloged a diverse microbial community in subsurface fluids draining from boreholes 3000 feet deep at Henderson Mine, CO, USA (Sahl et al., 2008). The prior characterization of the fluid chemistry and microbial community forms the basis for the further investigation here of the source of NH(4)(+). The reported fluid chemistry included N(2), NH(4)(+) (5–112 μM), NO(2)(−) (27–48 μM), and NO(3)(−) (17–72 μM). In this study, the correlation between low NH(4)(+) concentrations in dominantly meteoric fluids and higher NH(4)(+) in rock-reacted fluids is used to hypothesize that NH(4)(+) is sourced from NH(4)(+)-bearing biotite. However, biotite samples from the host rocks and ore-body minerals were analyzed by Fourier transform infrared (FTIR) microscopy and none-contained NH(4)(+). However, the nitrogenase-encoding gene nifH was successfully amplified from DNA of the fluid sample with high NH(4)(+), suggesting that subsurface microbes have the capability to fix N(2). If so, unregulated nitrogen fixation may account for the relatively high NH(4)(+) concentrations in the fluids. Additionally, the amoA and nxrB genes for archaeal ammonium monooxygenase and nitrite oxidoreductase, respectively, were amplified from the high NH(4)(+) fluid DNA, while bacterial amoA genes were not. Putative nitrifying organisms are closely related to ammonium-oxidizing Crenarchaeota and nitrite-oxidizing Nitrospira detected in other subsurface sites based upon 16S rRNA sequence analysis. Thermodynamic calculations underscore the importance of NH(4)(+) as an energy source in a subsurface nitrification pathway. These results suggest that the subsurface microbial community at Henderson is adapted to the low nutrient and energy environment by their capability of fixing nitrogen, and that fixed nitrogen may support subsurface biomass via nitrification

“Candidatus Chlorobium masyuteum,” a Novel Photoferrotrophic Green Sulfur Bacterium Enriched From a Ferruginous Meromictic Lake

Anoxygenic phototrophic bacteria can be important primary producers in some meromictic lakes. Green sulfur bacteria (GSB) have been detected in ferruginous lakes, with some evidence that they are photosynthesizing using Fe(II) as an electron donor (i.e., photoferrotrophy). However, some photoferrotrophic GSB can also utilize reduced sulfur compounds, complicating the interpretation of Fe-dependent photosynthetic primary productivity. An enrichment (BLA1) from meromictic ferruginous Brownie Lake, Minnesota, United States, contains an Fe(II)-oxidizing GSB and a metabolically flexible putative Fe(III)-reducing anaerobe. “Candidatus Chlorobium masyuteum” grows photoautotrophically with Fe(II) and possesses the putative Fe(II) oxidase-encoding cyc2 gene also known from oxygen-dependent Fe(II)-oxidizing bacteria. It lacks genes for oxidation of reduced sulfur compounds. Its genome encodes for hydrogenases and a reverse TCA cycle that may allow it to utilize H2 and acetate as electron donors, an inference supported by the abundance of this organism when the enrichment was supplied by these substrates and light. The anaerobe “Candidatus Pseudopelobacter ferreus” is in low abundance (∼1%) in BLA1 and is a putative Fe(III)-reducing bacterium from the Geobacterales ord. nov. While “Ca. C. masyuteum” is closely related to the photoferrotrophs C. ferroooxidans strain KoFox and C. phaeoferrooxidans strain KB01, it is unique at the genomic level. The main light-harvesting molecule was identified as bacteriochlorophyll c with accessory carotenoids of the chlorobactene series. BLA1 optimally oxidizes Fe(II) at a pH of 6.8, and the rate of Fe(II) oxidation was 0.63 ± 0.069 mmol day–1, comparable to other photoferrotrophic GSB cultures or enrichments. Investigation of BLA1 expands the genetic basis for phototrophic Fe(II) oxidation by GSB and highlights the role these organisms may play in Fe(II) oxidation and carbon cycling in ferruginous lakes.This article is published as Lambrecht N, Stevenson Z, Sheik CS, Pronschinske MA, Tong H and Swanner ED (2021) “Candidatus Chlorobium masyuteum,” a Novel Photoferrotrophic Green Sulfur Bacterium Enriched From a Ferruginous Meromictic Lake. Front. Microbiol. 12:695260. doi: 10.3389/fmicb.2021.695260. Posted with permission. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms

Subsurface Microbial Diversity in Deep-Granitic-Fracture Water in Colorado▿

A microbial community analysis using 16S rRNA gene sequencing was performed on borehole water and a granite rock core from Henderson Mine, a >1,000-meter-deep molybdenum mine near Empire, CO. Chemical analysis of borehole water at two separate depths (1,044 m and 1,004 m below the mine entrance) suggests that a sharp chemical gradient exists, likely from the mixing of two distinct subsurface fluids, one metal rich and one relatively dilute; this has created unique niches for microorganisms. The microbial community analyzed from filtered, oxic borehole water indicated an abundance of sequences from iron-oxidizing bacteria (Gallionella spp.) and was compared to the community from the same borehole after 2 weeks of being plugged with an expandable packer. Statistical analyses with UniFrac revealed a significant shift in community structure following the addition of the packer. Phospholipid fatty acid (PLFA) analysis suggested that Nitrosomonadales dominated the oxic borehole, while PLFAs indicative of anaerobic bacteria were most abundant in the samples from the plugged borehole. Microbial sequences were represented primarily by Firmicutes, Proteobacteria, and a lineage of sequences which did not group with any identified bacterial division; phylogenetic analyses confirmed the presence of a novel candidate division. This “Henderson candidate division” dominated the clone libraries from the dilute anoxic fluids. Sequences obtained from the granitic rock core (1,740 m below the surface) were represented by the divisions Proteobacteria (primarily the family Ralstoniaceae) and Firmicutes. Sequences grouping within Ralstoniaceae were also found in the clone libraries from metal-rich fluids yet were absent in more dilute fluids. Lineage-specific comparisons, combined with phylogenetic statistical analyses, show that geochemical variance has an important effect on microbial community structure in deep, subsurface systems

Phytoplankton contributions to the trace-element composition of Precambrian banded iron formations

Banded iron formations are economically important sedimentary deposits in Earth's Precambrian rock record, consisting of alternating iron-rich (hematite, magnetite, and siderite) and silicate/carbonate (quartz, claylike minerals, dolomite, and ankerite) layers. Based on chemical analyses from banded iron formation units of the 2.48 Ga Dales Gorge Member of the Hamersley Group in Western Australia, it has been previously suggested that most, if not all, of the iron in banded iron formations could have been oxidized by anoxygenic phototrophic bacteria (photoferrotrophs) at cell densities considerably less than those found in modern iron-rich aqueous environments. However, oxygen-producing phytoplankton may have also been capable of supplying the necessary oxidizing power. Here, we revisit the question of the anoxygenic and oxygenic phytoplankton populations necessary to account for banded iron formation deposition and quantify the amount of selected trace elements (P, Mn, Co, Ni, Cu, Zn, Mo, Cd) that could have been associated with their biomass. Using an expanded geochemical data set for the Dales Gorge Member as an example, we find that with turnover times comparable to those seen in modern ecosystems, the same phytoplankton populations required to form banded iron formations could have supplied the entirety of trace elements found in this iron-rich deposit. Further, spurred by the similarities between banded iron formation and anoxygenic phytoplankton trace-element stoichiometries, we suggest that much of the trace-element inventory preserved in the banded iron formation was at some point biologically assimilated in the water column, released from degrading photoferrotrophic biomass at the seafloor and in the sediment pile, and ultimately fixed in the iron-rich sediment in approximately stoichiometric proportions by near-quantitative adsorption to ferrihydrite. Our observations suggest that, as today, phytoplankton and the recycling of their biomass exerted control over the trace-element composition of ancient seawater and sediment