Browsing by Subject "degradation"

Now showing 1 - 5 of 5
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    Accumulation of recalcitrant dissolved organic matter in aerobic aquatic systems
    (2021-02-09) Cotner, James; Anderson, NJ; Osburn, Christopher; cotne002@umn.edu; Cotner, James; Cotner Lab
    An oxygenated atmosphere led to many changes to life on Earth but it also provided a negative feedback to organic matter accumulation over billions of years by increasing decomposition rates. Nonetheless, dissolved organic carbon (DOC) is a huge carbon pool (>750 Pg) and it can accumulate to high concentrations (20-100 mg C L-1) in some freshwater aquatic systems, yet it is not clear why. Here, we examine DOC in several arctic lakes with varying concentrations and identify processes that alter its composition to make it recalcitrant to further degradation processes. Aging of DOC (from radiocarbon Δ14C ratios) corresponded with changes in its concentration, degradation rates, δ13C-DOC isotope ratios and optical quality, all suggesting that photochemical and microbial degradation processes contributed to decreased DOC reactivity over time. The degradation of young DOC was strongly stimulated by inorganic phosphorus, but older DOC was not, suggesting an important role for nutrients in regulating organic carbon degradation rates and pool sizes. Photochemical processing coupled with decreased habitat and microbial diversity in hydrologically isolated systems may enable recalcitrant DOC to accumulate with important implications for the Earth's carbon and oxygen cycles.
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    Deciphering the mechanism of Transferrin Receptor mRNA degradation under iron replete conditions
    (2016-05) Rupani, Dhwani
    Iron is an essential co-factor required for many biochemical reactions in our body, however iron overload can be detrimental to the cells. Thus, intra-cellular iron concentration is meticulously controlled. For most cells in the body, the transferrin receptor (TFRC-1) is the major means through which iron is imported into the cell. Influx of transferrin bound iron is regulated by changes in the stability of TFRC-1 mRNA. Under iron deplete conditions, iron regulatory proteins 1 and 2 (IRP-1 & 2) bind to specific sequence elements within the 3’ untranslated region (3’UTR) of the TFRC-1 mRNA and prevent its degradation. Whereas under iron replete conditions there is minimal binding between the IRPs and TFRC-1 mRNA, resulting in TFRC-1 mRNA degradation, the precise mechanism of which is yet unknown. This study was based on three hypotheses that could lead to identification of the mechanism of TFRC-1 mRNA degradation. First, there could be a microRNA mediated silencing of the TFRC-1 mRNA. Secondly, the TFRC-1 mRNA could catalyse its own degradation or lastly an iron responsive endonuclease could degrade the TFRC-1 mRNA. Using a luciferase reporter system, we have performed a detailed mutagenesis study of a previously minimized TFRC-1 construct and identified three critical elements for degradation. The three elements impart a graded response to stability and a similar graded response is also observed in endogenous TFRC-1 mRNA under certain conditions. Results from the mutagenesis study strongly suggest that an unidentified endonuclease is responsible for degradation. Identifying this endonuclease will provide a novel therapeutic target to manipulate iron concentration in pathological cells.
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    Factors Controlling the Decomposition of Ectomycorrhizal Fungal Tissue and the Formation of Soil Organic Matter
    (2019-06) Ryan, Maeve Elizabeth
    The turnover of ectomycorrhizal (ECM) fungi accounts for up to half of the organic carbon found in forest soils and therefore represents an important pathway for the removal of carbon from the atmosphere to be stored belowground as long-lived soil organic matter (SOM). Understanding the flux of fungal necromass inputs to SOM, and their subsequent stabilization potential in forest soils, requires an understanding of the chemical changes that occur during the degradation of fungal tissue. Additionally, it is hypothesized that degradation of fungal necromass is slowed by high melanin content and accelerated by high nitrogen content. A field degradation study was carried out at the Cedar Creek Ecosystem Science Reserve in East Bethel, Minnesota. Necromass from four species of ECM fungi with varying degrees of melanization was buried in litter bags in a Pinus-dominated forest below the soil litter layer, allowed to degrade naturally, and harvested nine times over a period of 90 days. Harvest was more frequent during the first week to gain insight into the dynamic early decomposition period. Elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR), and thermochemolysis-gas chromatography-mass spectrometry (pyGCMS), including novel methods of quantifying the contribution from various types of biopolymers to the total remaining tissue, supplement mass loss data to provide an overview of the chemical changes that occur as fungal necromass decomposes. Each of the four species lost a significant amount of mass in the first seven days of incubation but, at the end of the three-month degradation sequence, a significant fraction of fungal necromass remained. This necromass was chemically distinct from undegraded necromass, containing more aromatic compounds, suggesting that the relative abundance of melanin, which is highly aromatic, increased as other cellular components degraded away. Although melanin content was hypothesized to slow degradation, a high-melanin species degraded at effectively the same rate as the two low-melanin species. Differences in degradation rates across species can be attributed to initial nitrogen content, while melanin content could explain differences in degradation rate within a species.
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    Quantifying Polymer Surface Degradation Using Fluorescence Spectroscopy
    (2023) Tigner, Jonathan
    One solution to minimizing plastic pollution is to improve reuse and recycling strategies. Recycling, however, is limited by the overall degradation of plastics being used. Photochemical or thermal driving forces facilitate the incorporation of oxygen into the backbone and chain cleavage; yet, current techniques for monitoring this plastic degradation fail to observe early stages of degradation, which is key for optimizing reusability. This research seeks to develop a cheap, reproducible, and nondestructive technique for monitoring degradation of polyethylene and polypropylene materials using Nile red as a fluorescent probe. Changes in Nile red’s fluorescence spectra were observed upon exposure to stained, aged polyethylene and polypropylene samples. As the surface hydrophobicity of the plastic decreases, Nile red’s fluorescence signal undergoes corresponding signal shift to longer wavelengths (lower energy). The trends seen in the fluorescent profile were related to more commonly used measurements of plastic degradation, namely carbonyl index from infrared spectroscopy and bulk crystallinity from calorimetry. Results demonstrate clear trends in fluorescence spectra shifts as related to the chemical and physical changes to the plastics, with trends dependent on polymer type but independent of polymer film thickness. The strength of this technique is divided into two defined fits of the fluorescence signal; one fit characterizes the degradation throughout the whole range of degradative oxidation and the other is tailored to provide insight into the early stages of degradation. Overall, this work establishes a characterization tool that assesses the extent of plastics’ degradation, which may ultimately impact our ability to recover plastics and minimize plastic waste.
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    Testing the Hydrolysis-Driven Degradation of Sutures: Impacts on Tensile Strength Over Time
    (2024-12-19) Madhaparia, Mihir
    This study investigates the rate of tensile strength loss in absorbable sutures due to hydrolytic degradation under simulated in vivo conditions. Sutures were subjected to tensile and degradation testing in a controlled environment to evaluate the impact of moisture and time on suture performance. Results indicate an initial increase in tensile strength upon hydration, followed by a progressive decline due to hydrolysis. These findings provide critical insights for surgeons regarding suture performance in high-stress environments, such as the fascia layer, and underscore the need for further research in dynamic loading and in vivo scenarios.