TY - THES A1 - Usmani, Shirin T1 - Wood treated with nano metal fluorides - relations between composition, size, and durability T2 - Wood Treated with Nano Metal Fluorides – Relations between Composition, Size, and Durability N2 - In this study, nanoscopic particles of magnesium Fluoride (MgF2) and calcium fluoride (CaF2) also known as nano metal fluorides (NMFs), were evaluated for their potential to improve wood durability. Even though these fluorides are sparingly soluble, their synthesis in the form of nano-sized particles turns them into promising candidates for wood preservation. Their distinct property of low-water solubility is proposed to maintain long-lasting protection of treated wood by reducing the leaching of fluoride. Analytical methods were used to characterize the synthesized NMFs and their distribution in treated wood specimens. Transmission electron microscopy images showed that these fluoride particles are smaller than 10 nm. In nano metal fluoride (NMF) treated specimens, aggregates of these particles are uniformly distributed in the wood matrix as confirmed with scanning electron microscopy images and their corresponding energy-dispersive X-ray spectroscopy maps. The fluoride aggregates form a protective layer around the tracheid walls and block the bordered pits, thus reducing the possible flow path for water absorption into wood. This is reflected in the reduced swelling and increased hydrophobicity of wood treated with NMFs. The biocidal efficacy of NMFs was tested against brown-rot fungi (Coniophora puteanaand Rhodonia placenta), white-rot fungus (Trametes versicolor), and termites (Coptotermes formosanus). The fungal and termite tests were performed in accordance with the EN 113 (1996) and EN 117 (2012) standards, respectively. Prior to fungal tests, the NMF treated wood specimens were leached according to the EN 84 (1997)standard. Compared to untreated specimens, the NMF treated wood specimens have a higher resistance to decay caused by brown-rot fungi, white-rot fungus, and termites. Although all NMF treatments in wood reduce the mass loss caused by fungal decay, only the combined treatment of MgF2 and CaF2 has efficacy against both brown-rot fungi and white-rot fungus. Similarly, wood treated with the combined NMF formulation is the least susceptible to attack by C. formosanus.It is proposed that combining MgF2 and CaF2changes their overall solubility to promote the release of fluoride ions at the optimal concentration needed for biocidal efficacy against fungi and termites. In this thesis, it was proven that even after leaching, sufficient fluoride was present to protect NMF treated wood from fungal decay. This shows that NMFs are robust enough for above ground contact outdoor applications of wood, where permanent wetness cannot be avoided according to Use Class 3.2, as per the EN 335 (2013) standard. Also, they pose a low risk to human health and the environment because they are sparingly soluble. Since NMFs significantly reduce the decay of wood, the CO2 fixed in it will be retained for longer than in unpreserved wood. Overall, the novel results of this study show the potential of NMFs to increase the service life of building materials made from non-durable wood. KW - Termites KW - Nano metal fluorides KW - Solubility KW - Wood protection KW - Fungi PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525108 DO - https://doi.org/10.18452/22553 SP - i EP - 118 PB - Humboldt-Universität zu Berlin CY - Berlin AN - OPUS4-52510 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Gerrits, Ruben T1 - An experimental study of fungal olivine weathering N2 - Free-living and (ecto)-mycorrhizal fungi enhance rock weathering. In their roles as mineral weathering agents and mutualistic partners of phototrophs, fungi supply primary producers like plants and phototrophic microorganisms with mineral-derived nutrients. The exact mechanisms behind fungus-induced mineral weathering processes are however not well understood. Progress can be achieved here by reproducible experimental simulations of the natural processes, using well-characterised model organisms and minerals. In this study, the weathering-affecting, rock-inhabiting fungus, Knufia petricola A95 and the Fe-bearing olivine (Fe0.2Mg1.8SiO4) were selected to investigate fungi-induced effects on mineral dissolution. The availability of a melanin-deficient mutant (ΔKppks) of K. petricola A95, that produced more extracellular polymeric substances (EPS) than the wild type (WT), enabled comparative studies of the role of melanin and EPS in weathering processes. Three experimental systems, which generate long-term microbiological stability, were developed to study the impact of the WT and ΔKppks on olivine weathering: (1) batch and (2) mixed flow dissolution experiments, and (3) biofilm cultivation experiments. In addition, state-of-the-art analytical techniques were used to monitor changes in the growth medium, as well as of the mineral surface and biofilm-mineral interface. Inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of the Mg, Si and Fe concentrations in the reacted growth medium was used to quantify olivine dissolution. In abiotic controls, Mg and Si dissolved congruently, while Fe precipitated. The measured olivine dissolution rates at pH 6 were two orders of magnitude lower than previously reported, but similar at acidic pH. X-ray photoelectron spectroscopy (XPS) analyses of the olivine surface confirmed the presence of Fe (oxyhydr)oxide precipitates. Transmission electron microscopy (TEM) imaging of an abiotically reacted polished olivine section from the long-term cultivation experiment showed the presence of an amorphous layer enriched in Fe. All these observations indicate that the precipitation of Fe (oxyhydr)oxides on the olivine surface inhibits olivine dissolution. Both tested rock-inhabiting fungal strains affect Fe precipitation as well as olivine dissolution. Evaluation of the WT and ΔKppks revealed that the WT formed less biomass but could take up higher amounts of metals (e.g. Fe) and was more efficient in its attachment to olivine. The WT and ΔKppks enhanced olivine dissolution as demonstrated by higher Mg and Si concentration in the reacted growth medium. They furthermore prevented Fe precipitation by binding Fe and retaining it in solution, thereby allowing olivine dissolution to proceed. The WT cells that were attached to the olivine surface were particularly efficient at inhibiting Fe precipitation. By binding Fe directly at the olivine surface, the WT cells removed the inhibition of olivine dissolution almost completely. TEM analysis of polished olivine sections, colonised by a fungal biofilm for seven months, supported this hypothesis. After long-term fungus-olivine interaction, the Fe-enriched, amorphous layer did not develop, and the olivine surface was stronger etched compared to the abiotic control. To study the effect of mutualism on mineral weathering, K. petricola was grown with the cyanobacterium, Nostoc punctiforme ATCC 29133. Both partners showed an enhanced growth and formed a stratified biofilm which attached more strongly to olivine. Nevertheless, the olivine dissolution rate of the fungus-cyanobacterium consortium was moderate. Rock weathering simulation systems developed here are promising research instruments. The experimental conditions allow for the alteration of the studied mineral surface, while the clear definition of these conditions delivers a stable growth of microorganisms. The latter makes these systems universally applicable, especially in combination with integrative multidisciplinary analytics. Processes underlying environmental and biological effects on rock weathering, metal corrosion, plastic degradation, or the deterioration of any other substrate can be studied reproducibly and over a long period of time. The chemical and biological complexity of these simulation systems mimics natural rock weathering processes. The mineral dissolution rates generated in this study are therefore relevant to natural ecosystems. KW - Olivine KW - Weathering KW - Fungus PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:188-refubium-25125-1 DO - https://doi.org/10.17169/refubium-2880 SP - 1 EP - 178 PB - Freie Universität Berlin CY - Berlin AN - OPUS4-48825 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - THES A1 - Breitenbach, Romy T1 - Biochemische und physiologische Charakterisierung der extrazellulären Matrix eines Modellbiofilms N2 - An der Grenzschicht zwischen einer festen Oberfläche und der umgebenden Luft wachsende subaerische Biofilme (SAB) zeichnen sich durch eine erhöhte Toleranz gegenüber extremen Umweltbedingungen und dem Eintrag von Bioziden aus. Dieser Schutz vor äußeren Umwelteinflüssen wird vornehmlich durch den Beitrag von extrazellulären polymeren Substanzen (EPS) und Pigmenten, wie Melanin und Carotinoiden, vieler unterschiedlicher Organismen gewährleistet. Deren Synthese wird wiederum durch intrazelluläre Botenstoffe reguliert. Das Cyanobakterium Nostoc punctiforme und der mikrokoloniale Pilz Knufia petricola, als Partner eines etablierten SAB-Modells und Vertreter zweier typischer Organismengruppen in SAB, wurden genutzt, um Botenstoffe und Pigmente genetisch zu manipulieren und die Biofilmmatrix dieser Mutanten strukturell zu untersuchen. In dieser Arbeit konnten erstmals die EPS beider Organismen extrahiert und die Struktur der extrazellulären Polysaccharide beschrieben werden. Daneben wurden die extrazellulären Polysaccharide von K. petricola Wildtyp mit denen verschiedener Pigmentmutanten verglichen. Das Fehlen des Schutzpigmentes Melanin führte zu einer ausgeprägteren extrazellulären Matrix in den Biofilmen. Gleichzeitig änderte sich die Struktur der extrazellulären Polysaccharide. Während der Wildtyp zu ~80% ein α-Glucan und zu ~20% ein α/β-Galaktomannan sekretierte, war der Anteil des Galaktomannans bei den Melaninmutanten erhöht. Das Ausschalten der Carotinoid-Synthese hatte jedoch keinen Einfluss auf die Beschaffenheit der extrazellulären Polysaccharide. Ein deutlich komplexeres extrazelluläres Polysaccharid aus acht verschiedenen Monosaccharid-Einheiten bildete N. punctiforme. Durch die Überproduktion des bakteriellen sekundären Botenstoffes c-di-GMP konnte zudem ein grundlegender Einfluss auf die Reaktion des Cyanobakteriums gegenüber externen Signalen und die damit verbundene Zelldifferenzierung gezeigt werden. Ein artifiziell erhöhtes c-di-GMP-Level in den Zellen führte zur Ausbildung eines sessilen Lebensstils durch Hemmung der Differenzierung motiler Hormogonien und vermehrte Produktion von EPS. Die Struktur der extrazellulären Polysaccharide wurde dadurch nicht verändert. Neben der strukturellen Analyse konnten die Veränderungen der extrazellulären Matrix beider Organismen zusätzlich durch mikroskopische Methoden visualisiert werden. Beide Organismen steuern komplexe Polymere, deren Produktion maßgeblich mit intrazellulären Faktoren verknüpft ist, zu der extrazellulären Matrix des Modellbiofilms bei. KW - Biofilm KW - EPS KW - Extrazelluläre Polysaccharide PY - 2018 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-471747 SP - 1 EP - 198 CY - Berlin AN - OPUS4-47174 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -