Manganese- and Iron-Dependent Marine Methane Oxidation Beal, Emily J.; House, Christopher H.; Orphan, Victoria J.
Science (American Association for the Advancement of Science),
07/2009, Letnik:
325, Številka:
5937
Journal Article
Recenzirano
Anaerobic methanotrophs help regulate Earth's climate and may have been an important part of the microbial ecosystem on the early Earth. The anaerobic oxidation of methane (AOM) is often thought of ...as a sulfate-dependent process, despite the fact that other electron acceptors are more energetically favorable. Here, we show that microorganisms from marine methane-seep sediment in the Eel River Basin in California are capable of using manganese (birnessite) and iron (ferrihydrite) to oxidize methane, revealing that marine AOM is coupled, either directly or indirectly, to a larger variety of oxidants than previously thought. Large amounts of manganese and iron are provided to oceans from rivers, indicating that manganese- and iron-dependent AOM have the potential to be globally important.
All terrestrial organisms depend on nucleic acids (RNA and DNA), which use pyrimidine and purine nucleobases to encode genetic information. Carbon-rich meteorites may have been important sources of ...organic compounds required for the emergence of life on the early Earth; however, the origin and formation of nucleobases in meteorites has been debated for over 50 y. So far, the few nucleobases reported in meteorites are biologically common and lacked the structural diversity typical of other indigenous meteoritic organics. Here, we investigated the abundance and distribution of nucleobases and nucleobase analogs in formic acid extracts of 12 different meteorites by liquid chromatography–mass spectrometry. The Murchison and Lonewolf Nunataks 94102 meteorites contained a diverse suite of nucleobases, which included three unusual and terrestrially rare nucleobase analogs: purine, 2,6-diaminopurine, and 6,8-diaminopurine. In a parallel experiment, we found an identical suite of nucleobases and nucleobase analogs generated in reactions of ammonium cyanide. Additionally, these nucleobase analogs were not detected above our parts-per-billion detection limits in any of the procedural blanks, control samples, a terrestrial soil sample, and an Antarctic ice sample. Our results demonstrate that the purines detected in meteorites are consistent with products of ammonium cyanide chemistry, which provides a plausible mechanism for their synthesis in the asteroid parent bodies, and strongly supports an extraterrestrial origin. The discovery of new nucleobase analogs in meteorites also expands the prebiotic molecular inventory available for constructing the first genetic molecules.
Obtaining carbon isotopic information for organic carbon from Martian sediments has long been a goal of planetary science, as it has the potential to elucidate the origin of such carbon and aspects ...of Martian carbon cycling. Carbon isotopic values (δ
C
) of the methane released during pyrolysis of 24 powder samples at Gale crater, Mars, show a high degree of variation (-137 ± 8‰ to +22 ± 10‰) when measured by the tunable laser spectrometer portion of the Sample Analysis at Mars instrument suite during evolved gas analysis. Included in these data are 10 measured δ
C values less than -70‰ found for six different sampling locations, all potentially associated with a possible paleosurface. There are multiple plausible explanations for the anomalously depleted
C observed in evolved methane, but no single explanation can be accepted without further research. Three possible explanations are the photolysis of biological methane released from the subsurface, photoreduction of atmospheric CO
, and deposition of cosmic dust during passage through a galactic molecular cloud. All three of these scenarios are unconventional, unlike processes common on Earth.
The Sample Analysis at Mars instrument stepped combustion experiment on a Yellowknife Bay mudstone at Gale crater, Mars revealed the presence of organic carbon of Martian and meteoritic origins. The ...combustion experiment was designed to access refractory organic carbon in Mars surface sediments by heating samples in the presence of oxygen to combust carbon to CO
2
. Four steps were performed, two at low temperatures (less than ∼550 °C) and two at high temperatures (up to ∼870 °C). More than 950 μg C/g was released at low temperatures (with an isotopic composition of δ
13
C = +1.5 ± 3.8‰) representing a minimum of 431 μg C/g indigenous organic and inorganic Martian carbon components. Above 550 °C, 273 ± 30 μg C/g was evolved as CO
2
and CO (with estimated δ
13
C = −32.9‰ to −10.1‰ for organic carbon). The source of high temperature organic carbon cannot be definitively confirmed by isotopic composition, which is consistent with macromolecular organic carbon of igneous origin, meteoritic infall, or diagenetically altered biomass, or a combination of these. If from allochthonous deposition, organic carbon could have supported both prebiotic organic chemistry and heterotrophic metabolism at Gale crater, Mars, at ∼3.5 Ga.
Thioamide bonds are important intermediates in prebiotic chemistry. In cyanosulfidic prebiotic chemistry, they serve as crucial intermediates in the pathways that lead to the formation of many ...important biomolecules (e.g., amino acids). They can also serve as purine and pyrimidine precursors, the two classes of heterocycle employed in genetic molecules. Despite their importance, the formation of thioamide bonds from nitriles under prebiotic conditions has required large excesses of sulfide or compounds with unknown prebiotic sources. Here, we describe the thiol-catalyzed formation of thioamide bonds from nitriles. We show that the formation of the simplest of these compounds, thioformamide, forms readily in spark-discharge experiments from hydrogen cyanide, sulfide, and a methanethiol catalyst, suggesting potential accumulation on early Earth. Lastly, we demonstrate that thioformamide has a Gibbs energy of hydrolysis (
Δ
G
r
∘
) comparable to other energy-currencies on early Earth such as pyrophosphate and thioester bonds. Overall, our findings imply that thioamides might have been abundant on early Earth and served a variety of functions during chemical evolution.
The subseafloor marine biosphere may be one of the largest reservoirs of microbial biomass on Earth and has recently been the subject of debate in terms of the composition of its microbial ...inhabitants, particularly on sediments from the Peru Margin. A metagenomic analysis was made by using whole-genome amplification and pyrosequencing of sediments from Ocean Drilling Program Site 1229 on the Peru Margin to further explore the microbial diversity and overall community composition within this environment. A total of 61.9 Mb of genetic material was sequenced from sediments at horizons 1, 16, 32, and 50 m below the seafloor. These depths include sediments from both primarily sulfate-reducing methane-generating regions of the sediment column. Many genes of the annotated genes, including those encoding ribosomal proteins, corresponded to those from the Chloroflexi and Euryarchaeota. However, analysis of the 16S small-subunit ribosomal genes suggests that Crenarchaeota are the abundant microbial member. Quantitative PCR confirms that uncultivated Crenarchaeota are indeed a major microbial group in these subsurface samples. These findings show that the marine subsurface is a distinct microbial habitat and is different from environments studied by metagenomics, especially because of the predominance of uncultivated archaeal groups.
Penciling in details of the Hadean House, Christopher H.
Proceedings of the National Academy of Sciences - PNAS,
11/2015, Letnik:
112, Številka:
47
Journal Article
Phosphorites can record oceanic conditions during their deposition, but the faithful retention of primary information in Paleoproterozoic deposits can be mitigated by post‐depositional processes. ...Here, we examine a peritidal phosphorite within a microbialite reef complex in the 2.4–2.2 Ga Turee Creek Group in Western Australia to assess the environmental information retained. Field mapping and petrography distinguishes between authigenic and locally transported phosphorite fragments, each of which contains unique information regarding the deposit. Elemental mapping and laser‐ablation analyses differentiate the impact of depositional versus early diagenetic versus metamorphic processes within these fragments. Samples within a near‐shore pebble conglomerate have mixed riverine‐oceanic signals and lack cerium anomalies, consistent with the depositional environment. Clasts from off‐shore peloidal grainstone beds retain “hat‐shaped” patterns with small negative cerium anomalies, reflective of transport and redeposition within potentially oxic seawater. U‐Pb isotopic dates range from ∼1.8 to 2.3 Ga and are generally uncorrelated with rare earth element and yttrium data. The youngest date (∼1.8 Ga) is associated with recrystallized apatite, with concave down, middle rare earth element enriched patterns. A potential depositional age, ∼2.3 Ga, is associated with massive apatite in a chert‐rich clast that has rare earth element patterns reflective of riverine‐oceanic signals. Overall, the peritidal system in the reef was dynamic, with potentially oxic seawater that had a strong riverine influence. Local recycling and reworking, early diagenesis, and later orogenic events impacted the preserved geochemical signals and together show that spatially resolved geochronological and geochemical data are ideal for interpreting ancient phosphorites.
Plain Language Summary
Understanding our ancient rock record is challenging because very few rocks are preserved from early Earth. Phosphorites are sedimentary deposits that are useful environmental archives because apatites can preserve primary chemical information. Here, we examined a shallow water phosphorite deposit from a reef complex in the c. 2.4–2.2 Ga Turee Creek Group to see what information is preserved. Knowing what the environment was like at this time will provide important insights into life at the time of the Great Oxidation Event. The phosphorite here contains a variety of textures of apatite, representative of different environmental and secondary processes, so we used spatially resolved techniques to study the different textures. Our data show that more chemically pristine apatite textures record a potentially oxic, mixed riverine‐oceanic signal, while others are more representative of transport and early diagenesis or metamorphism. Overall, we show that deep‐time phosphorites are useful archives for environmental information and that life at this time may have encountered oxygenated water in the very shallow oceans.
Key Points
Spatially resolved data differentiate depositional and secondary information from a peritidal phosphorite in a Paleoproterozoic microbialite reef complex
Apatite rare earth element data indicate a mixed riverine‐oceanic, potentially oxic signal for the depositional environment
Apatite U‐Pb data show a prospective depositional/early diagenetic age (∼2.3 Ga) alongside ages coincident with regional orogenic events at ∼2.1 and ∼1.8 Ga
Numerous archaeal lineages are known to inhabit marine subsurface sediments, although their distributions, metabolic capacities, and interspecies interactions are still not well understood. Abundant ...and diverse archaea were recently reported in Costa Rica (CR) margin subseafloor sediments recovered during IODP Expedition 334. Here, we recover metagenome-assembled genomes (MAGs) of archaea from the CR margin and compare them to their relatives from shallower settings. We describe 31 MAGs of six different archaeal lineages (Lokiarchaeota, Thorarchaeota, Heimdallarchaeota, Bathyarcheota, Thermoplasmatales, and Hadesarchaea) and thoroughly analyze representative MAGs from the phyla Lokiarchaeota and Bathyarchaeota. Our analysis suggests the potential capability of Lokiarchaeota members to anaerobically degrade aliphatic and aromatic hydrocarbons. We show it is genetically possible and energetically feasible for Lokiarchaeota to degrade benzoate if they associate with organisms using nitrate, nitrite, and sulfite as electron acceptors, which suggests a possibility of syntrophic relationships between Lokiarchaeota and nitrite and sulfite reducing bacteria. The novel Bathyarchaeota lineage possesses an incomplete methanogenesis pathway lacking the methyl coenzyme M reductase complex and encodes a noncanonical acetogenic pathway potentially coupling methylotrophy to acetogenesis via the methyl branch of Wood-Ljungdahl pathway. These metabolic characteristics suggest the potential of this Bathyarchaeota lineage to be a transition between methanogenic and acetogenic Bathyarchaeota lineages. This work expands our knowledge about the metabolic functional repertoire of marine benthic archaea.
biomarker based on the stable isotopes of nickel Cameron, Vyllinniskii; Vance, Derek; Archer, Corey ...
Proceedings of the National Academy of Sciences - PNAS,
07/2009, Letnik:
106, Številka:
27
Journal Article
Recenzirano
Odprti dostop
The new stable isotope systems of transition metals are increasingly used to understand and quantify the impact of primitive microbial metabolisms on the modern and ancient Earth. To date, little ...effort has been expended on nickel (Ni) isotopes but there are good reasons to believe that this system may be more straightforward, and useful in this respect, than some others. Here, we present Ni stable isotope data for abiotic terrestrial samples and pure cultures of methanogens. The dataset for rocks reveals little isotopic variability and provides a lithologic baseline for terrestrial Ni isotope studies. In contrast, methanogens assimilate the light isotopes, yielding residual media with a complementary heavy isotopic enrichment. Methanogenesis may have evolved during or before the Archean, when methane could have been key to Earth's early systems. Our data suggest significant potential in Ni stable isotopes for identifying and quantifying methanogenesis on the early planet. Additionally, Ni stable isotope fractionation may well prove to be the fundamental unambiguous trace metal biomarker for methanogens.
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