| 1. |
- Huld, Sigrid, et al.
(författare)
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Chemical Gardens Mimic Electron Paramagnetic Resonance Spectra and Morphology of Biogenic Mn Oxides
- 2023
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Ingår i: Astrobiology. - : Mary Ann Liebert. - 1531-1074 .- 1557-8070. ; 23:1, s. 24-32
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Tidskriftsartikel (refereegranskat)abstract
- Manganese (Mn) oxides are ubiquitous in nature and occur as both biological and abiotic minerals, but empirically distinguishing between the two remains a problem. Recently, electron paramagnetic resonance (EPR) spectroscopy has been proposed for this purpose. It has been reported that biogenic Mn oxides display a characteristic narrow linewidth in contrast to their pure abiotic counterparts, which is explained in part by the large number of cation vacancies that form within the layers of biogenic Mn oxides. It was, therefore, proposed that natural samples that display a narrow EPR linewidth, delta H-pp < 580G, could be assigned to a biogenic origin. However, in poorly crystalline or amorphous solids, both dipolar broadening and exchange narrowing simultaneously determine the linewidth. Considering that the spectral linewidth is governed by several mechanisms, this approach might be questioned. In this study, we report synthetic chemical garden Mn oxide biomorphs that exhibit both morphologically life-like structures and narrow EPR linewidths, suggesting that a narrow EPR line may be unsuitable as reliable evidence in assessment of biogenicity. Key Words: Mn oxides & mdash;EPR & mdash;Chemical gardens & mdash;Biomorphs. Astrobiology 23, 24-32.
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| 2. |
- Huld, Sigrid, et al.
(författare)
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Experimental mineralisation in carbonate, phosphate, and silicate of the filamentous hydrogenotrophic methanogen Methanobacterium oryzae
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Methanogens are thought to be some of the most ancient organisms to have lived on Earth. Fossils of ancient mineralised filamentous forms have been described before from hydrothermal vents to sediments. The peculiarity of Archaea lies in their cell walls, where they lack the peptidoglycan layer found in Bacteria and instead have a proteinaceous S-layer that has been shown to promote mineralisation through the presence of charged polymers on the cell surface. Some methanogens, like the filamentous Methanobacterium oryzae do not have an S-layer but a cell wall made of pseudomurein, similar in structure to bacterial murein. In this work, experimental mineralisation with carbonate, phosphate, and silica on a strain of M. oryzae were analysed. Differences in the degree of morphological preservation in the various fossilisation agents were observed over a period of 3 months and chemical analyses using EDX and XRD were carried out on precipitates. Results indicate that the various minerals precipitate differently in association with the methanogens and only silica replicates the morphology with a relatively high degree of fidelity. This shows the presence of possible taphonomic biases in the rock record depending on mineralisation, size differences, and cell wall structure. Therefore, this work has important outcomes for the recognition of filamentous fossils in the rock record and on the different mineralisation mechanisms on early Earth.
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| 3. |
- Huld, Sigrid
(författare)
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Untangling ambiguities in the microbial fossil record : experimental abiotic and biological approaches
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Life on early earth has long been the topic of discussion for many researchers: how did it come to be? Which cells came first? Where can we find them? The most ancient rocks on our planet may hold some of the answers to these questions, but many may only be answered in laboratories. Chemical and morphological traces can be found from Archaean deposits, tantalisingly similar to modern day prokaryotes. Often, they are interpreted as the fossilised remains of bacteria or archaea. However, the caveat remains the abiotic mechanisms with which many similar traces and markers can be formed. The purpose of this thesis was to look into the similarities and differences in abiotic and biological formation of filamentous structures in rocks and observe whether there are chemical or morphological factors that allow for distinguishing between the two. Various laboratory methods were used: chemical gardens to form filamentous abiotic structures and experimental mineralisation of a filamentous methanogen in carbonate, phosphate, and silicate in order to compare and contrast the various mineralisation mechanisms in the fidelity of preservation of the microbes. In the former experiment, analysis with electron paramagnetic resonance (EPR) spectroscopy was carried out to identify potential chemical biomarkers. A combination of scanning and transmission electron microscopy, energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Raman spectroscopy were also used to analyse the minerals and precipitates formed in both sets of experiments. The results of this research indicate that morphology of filamentous structures and the chemical signatures in biominerals may not be reliable as biogenic indicators. Furthermore, the work on experimental mineralisation reveals the possible biases in the rock record of microbial preservation which is highly dependent on the structure of the cell wall, chemistry of the environment, and the mineral formed. Finally, this work has important outcomes for the search for biomarkers on earth and on other planets and for the recognition of pseudofossils versus microbial fossils in the rock record.
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| 4. |
- Qvarnström, Martin, et al.
(författare)
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Exceptionally preserved beetles in a Triassic coprolite of putative dinosauriform origin
- 2021
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Ingår i: Current Biology. - : Elsevier. - 0960-9822 .- 1879-0445. ; 31:15, s. 3374-
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Tidskriftsartikel (refereegranskat)abstract
- The Triassic was a crucial period for the early evolution and diversification of insects, including Coleoptera(1-3)-the most diverse order of organisms on Earth. The study of Triassic beetles, however, relies almost exclusively on flattened fossils with limited character preservation. Using synchrotron microtomography, we investigated a fragmentary Upper Triassic coprolite, which contains a rich record of 3D-preserved minute beetle remains of Triamyxa coprolithica gen. et sp. nov. Some specimens are nearly complete, preserving delicate structures of the legs and antennae. Most of them are congruent morphologically, implying that they are conspecific. Phylogenetic analyses suggest that T. coprolithica is a member of Myxophaga, a small suborder of beetles with a sparse fossil record, and that it represents the only member of the extinct family Triamyxidae fam. nov. Our findings highlight that coprolites can contain insect remains, which are almost as well preserved as in amber. They are thus an important source of information for exploring insect evolution before the Cretaceous-Neogene "amber time window."Treated as food residues, insect remains preserved in coprolites also have important implications for the paleoecology of insectivores, in this case, likely the dinosauriform Silesaurus opolensis.
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| 5. |
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