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  • 1
    Publication Date: 2018-01-23
    Print ISSN: 0037-0746
    Electronic ISSN: 1365-3091
    Topics: Geosciences
    Published by Wiley
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  • 2
  • 3
    Publication Date: 2021-02-08
    Description: The earliest diagenetic post-mortem exposure of biogenic carbonates at the sea floor and in the uppermost sediment column results in the colonization of hard-part surfaces by bacterial communities. Some of the metabolic redox processes related to these communities have the potential to alter carbonate shell properties, and hence affect earliest diagenetic pathways with significant consequences for archive data. During a three-month in vitro study, shell subsamples of the ocean quahog Arctica islandica (Linnaeus, 1767) were incubated in natural anoxic sediment slurries and bacterial culture medium of the heterotrophic Shewanella sediminisHAW-EB3. Bulk analyses of the liquid media from the Shewanella sediminis incubation revealed an over ten-fold increase in total alkalinity, dissolved inorganic carbon and ΩAragonite, and the alteration of the Mg/Ca, Mg/Sr and Sr/Ca ratios relative to control incubations without cultures. Ion ratios were most affected in the incubation with anoxic sediment, depicting a 25% decrease in Mg/Ca relative to the control. Shell sample surfaces that were exposed to both incubations displayed visible surface dissolution features, and an 8 wt% loss in calcium content. No such alteration features were detected in control shells. Apparently, alteration of shell carbonate properties was induced by microbially driven decomposition of shell intercrystalline organic constituents and subsequent opening of pathways for pore fluid-crystal exchange. This study illustrates the potential influence of benthic bacterial metabolism on biogenic carbonate archives during the initial stages of diagenetic alteration within a relatively short experimental duration of only three months. These results suggest that foremost the biological effect of bacterial cation adsorption on divalent cation ratios has the potential to complicate proxy interpretation. Results shown here highlight the necessity to consider bacterial metabolic activities in marine sediments for the interpretation of palaeo-environmental proxies from shell carbonate archives.
    Type: Article , PeerReviewed
    Format: text
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  • 4
    Publication Date: 2024-02-07
    Description: Carbonates that exhibit obvious diagenetic alteration are usually excluded as archives in palaeoenvironmental studies. However, the potential impact of microbial alteration during early diagenesis is still poorly explored. To investigate the sensitivity of sulphur concentration, distribution, oxidation state and isotopic composition in marine aragonite to microbial alteration, Arctica islandica bivalves and Porites sp. corals were experimentally exposed to anaerobic microbial activity. The anoxic incubation media included a benthic bacterial strain Shewanella sediminis and a natural anoxic sediment slurry with a natural microbial community of unknown species. Combined fluorescence microscopy and synchrotron‐based analysis of the sulphur distribution and oxidation state enabled a comparison of organic matter and sulphur content in the two materials. Results revealed a higher proportion of reduced sulphur species and locally stronger fluorescence within the pristine bivalve shell compared to the pristine coral skeleton. Within the pristine bivalve specimen, reduced sulphur was enriched in layers along the inner shell margin. After incubation in the anoxic sediment slurry, this region revealed rust‐brown staining and a patchy S2‐ distribution pattern rather than S2‐‐layers. Another effect on sulphur distribution was rust‐brown coloured fibres along one growth line, revealing a locally higher proportion of sulphur. The δ34S value of carbonate‐associated sulphate remained largely unaffected by both incubation media, but a lower δ34S value of water‐soluble sulphate reflected the degradation of insoluble organic matter by microbes in both experiments. No significant alteration was detected in the coral samples exposed to microbial alteration. The data clearly identified a distinct sensitivity of organically bound sulphur in biogenic aragonite to microbial alteration even when “traditional” geochemical proxies such as δ18OCARB or δ13CCARB in the carbonate didn’t show any effect. Differences in the intensity of microbial alteration documented are likely due to inherent variations in the concentration and nature of original organic compositions in the samples.
    Type: Article , PeerReviewed
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  • 5
    Publication Date: 2017-01-06
    Description: Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pallial mantle could be induced in central mantle tissue underlying the damaged shell areas. This experimental approach makes it possible to identify gene products that control the chemical micro-environment during calcification as well as organic matrix components. This is unlike existing methodological approaches that work retroactively to characterize calcification relevant molecules and are just able to examine organic matrix components that are present in completed shells. In our assay an orthogonal array of nine 1 mm holes was drilled into the left valve, and mussels were suspended in net cages for 20, 29 and 36 days to regenerate. Structural observations using stereo-microscopy, SEM and Raman spectroscopy revealed organic sheet synthesis (day 20) as the first step of shell-repair followed by the deposition of calcite crystals (days 20 and 29) and aragonite tablets (day 36). The regeneration period was characterized by time-dependent shifts in gene expression in left central mantle tissue underlying the injured shell, (i) increased expression of two tyrosinase isoforms (TYR3: 29-fold and TYR6: 5-fold) at day 20 with a decline thereafter, (ii) an increase in expression of a gene encoding a nacrein-like protein (max. 100-fold) on day 29. The expression of an acidic Asp-Ser-rich protein was enhanced during the entire regeneration process. This proof-of-principle study demonstrates that genes that are specifically expressed in pallial and marginal mantle tissue can be induced (4 out of 10 genes) in central mantle following experimental injury of the overlying shell. Our findings suggest that regeneration assays can be used systematically to better characterize gene products that are essential for distinct phases of the shell formation process, particularly those that are not incorporated into the organic shell matrix.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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