Fucoidan degradation by marine bacteria

The oceans are an important carbon sink that have sequestered about half of all anthropogenic CO2 emissions. Marine carbon cycling is driven by the deposition of photosynthetic micro- and macroalgae in ocean sediments, where carbon is stored over thousands of years. The algal polysaccharide fucoidan is considered to be recalcitrant to microbial degradation and may therefore facilitate long-term carbon storage. Yet, factors that render fucoidan recalcitrant against microbial degradation remain unidentified, hampering our understanding of fucoidans in the carbon cycle. Fucoidans originating from the cell wall of brown algae are often co-extracted with other cell wall components. In Chapter I, I develop a simple step-wise protocol to purify fucoidans from different brown algae. Using mass spectrometry and nuclear magnetic resonance analyses, I describe the highly diverse and branched structures of different fucoidans. In Chapter II, I examine how marine bacteria degrade those complex branched fucoidans. Using genomics, proteomics and biochemistry, I characterize the newly isolated Verrucomicrobium a Lentimonasa sp. CC4 and show that fucoidan degradation requires highly dedicated pathways of over 100 enzymes covering 20% of the a Lentimonasa sp. CC4 proteome. The complexity of these pathways implies that only highly specialized bacteria can effectively degrade fucoidans and gives a clue why it may be recalcitrant. The proteomic analysis of a Lentimonasa sp. CC4 in chapter II suggested that two protein families, S1 15 and GH29, are key in fucoidan degradation. In Chapter III, I biochemically and structurally characterize one S1 15 sulfatase and one GH29 fucosidase, revealing their exo-enzyme activity and a novel catalytic pair of two aspartate residues. This provides insights into the molecular mechanism of exo-enzymatic fucoidan degradation. In Chapter IV, I trace the dynamics of different polysaccharides during a diatom spring bloom in Helgoland. I found that the dominant bloom-forming diatom Chaetoceros socialis secretes fucoidan in dissolved form, which aggregates and accumulates in particles at the end of the bloom. Known enzymes to degrade this polysaccharide are not expressed in the microbial community which indicates that fucoidans are not microbially degraded and act as vector for organic carbon drawdown. To summarize, fucoidans are diverse, highly branched polysaccharides whose degradation requires a large set of enzymes found in very few specialized marine bacteria. Their stability-enhancing properties lead to increased brown algal deposition in coastal sediments and in the open ocean they may acts as aggregation nuclei that enhance aggregation and settling of phytoplankton aggregates. Their abundance, recalcitrant nature and stickiness make fucoidans a likely key players in oceanic carbon sequestration

Constitutional Review of Socijal Law-Reforms in Germany and Its Impact on Legislation/Nadzor ustavnosti reformi socijalnih propisa u Njemačkoj i njegov utjecaj na zakonodavstvo

Značaj nadzora ustavnosti u odnosu na socijalno zakonodavstvo u Njemačkoj postaje očit kada se sagleda brojnost ustavnosudskih predmeta koji obuhvaćaju različite socijalne kategorije te utjecaj takvih odluka na socijalnu politiku i zakonodavstvo. Jednakost pred zakonom i načelo socijalne države blagostanja samo su dvije primjenjive ustavne odredbe, no one sadrže temeljne standarde za odlučivanje. Primjena načela jednakosti pred zakonom prilikom ocjene ustavnosti zahtijeva stavljanje u odnos konkretnih kategorija. Ustavni sud utvrđuje eventualna neustavna razlikovanja na zahtjev ovlaštene stranke. U slučaju utvrđenja povrede jednakosti pred zakonom, Ustavni sud može naložiti zakonodavcu da redefinira određene kategorije. Zakonodavac tako ima zadaću stvoriti i preurediti društveni poredak u okvirima koje postavlja Ustav koristeći pri tome široke diskrecijske ovlasti. Posebno se razmatraju najnovije reforme modernih usluga na tržištu rada radi odgovarajuće ilustracije izazova koji su vezani uz smanjenje izdataka iz državnog proračuna

Quantum size effects and carrier dynamics in two-dimensional lead halide perovskite nanostructures

In recent years, lead halide perovskites have not only proven to be a promising material for solar cell applications, but they have also shown a huge potential for light-emitting devices and other optoelectronic applications. Most of the initial studies focused on bulk perovskite materials. However, emerging colloidal perovskite nanocrystals have been shown to exhibit superior qualities relating to their efficiency and functionality. On the nanoscale, size-dependent effects can be exploited to tune the nanocrystals’ properties. In the present work, two-dimensional perovskite nanoplatelets and quasi-two-dimensional layered hybrid perovskites are investigated. A new and systematic variation of the ligand concentration during the nanocrystal synthesis is presented. This enables the fabrication of colloidal two-dimensional methylammonium lead bromide perovskite nanoplatelets of varying thicknesses down to only a single unit cell. Photoluminescence and absorption spectra show the appearance of clear excitonic features in the thinnest structures and a blue-shift in the emission wavelength of more than 90 nm in comparison to the bulk counterpart. Additionally, in the thinnest structures the exciton binding energy increases up to several hundreds of meV due to a reduced excitonic screening. For the first time the quantum size effect in these nanoplatelets is quantitatively described through model calculations. Miniband formation in the multilayer structures lowers the emission energy with respect to the isolated nanoplatelet. Thickness-dependent photoluminescence lifetime measurements are performed. The recorded lifetimes decrease with thinner nanoplatelets as the exciton binding energy increases. Temperature-dependent photoluminescence measurements on cesium lead bromide perovskite nanoplatelets are carried out. A theoretical model considering acoustic and optical phonons as the main sources for scattering of excitons, shows that the former dominate at temperatures below 90 K and the latter above this temperature. Interestingly, temperature-dependent time-resolved photoluminescence measurements display contributions of bright and dark excitons to the decay curves below 60 K. At higher temperatures an antiquenching behavior of the luminescence is observed, indicating that ligands play an important role in these structures with a high surface-to-volume ratio. The interlayer distance in layered hybrid perovskites is systematically varied to investigate its impact on structure-function relationships and electronic coupling between the perovskite layers. It is found that the optical bandgap is determined mainly by two parameters. First, the length of the organic ligands separating the inorganic perovskite sheets influences the tilt angle of the perovskite octahedra. An increase of the optical bandgap with larger tilt angles is observed. Secondly, electronic coupling between the perovskite sheets constituting the multilayer structures is found to have an impact on the bandgap, albeit significantly smaller than the effect induced by the change in tilt angles. Importantly, the electronic coupling only occurs for perovskite multilayers with an interlayer distance below 1.5 nm. This thesis contributes to a fundamental understanding of optical properties of two-dimensional perovskites. It focuses on thickness-dependent quantum size effects, exciton-phonon interactions, and structure-function relationships

Identity, abundance and reactivation kinetics of thermophilic fermentative endospores in cold marine sediment and seawater

Cold marine sediments harbor endospores of fermentative and sulfate-reducing, thermophilic bacteria. These dormant populations of endospores are believed to accumulate in the seabed via passive dispersal by ocean currents followed by sedimentation from the water column. However, the magnitude of this process is poorly understood because the endospores present in seawater were so far not identified, and only the abundance of thermophilic sulfate-reducing endospores in the seabed has been quantified. We investigated the distribution of thermophilic fermentative endospores (TFEs) in water column and sediment of Aarhus Bay, Denmark, to test the role of suspended dispersal and determine the rate of endospore deposition and the endospore abundance in the sediment. We furthermore aimed to determine the time course of reactivation of the germinating TFEs. TFEs were induced to germinate and grow by incubating pasteurized sediment and water samples anaerobically at 50 degrees C. We observed a sudden release of the endospore component dipicolinic acid immediately upon incubation suggesting fast endospore reactivation in response to heating. Volatile fatty acids (VFAs) and H-2 began to accumulate exponentially after 3.5 h of incubation showing that reactivation was followed by a short phase of outgrowth before germinated cells began to divide. Thermophilic fermenters were mainly present in the sediment as endospores because the rate of VFA accumulation was identical in pasteurized and non-pasteurized samples. Germinating TFEs were identified taxonomically by reverse transcription, PCR amplification and sequencing of 16S rRNA. The water column and sediment shared the same phylotypes, thereby confirming the potential for seawater dispersal. The abundance of TFEs was estimated by most probable number enumeration, rates of VFA production, and released amounts of dipicolinic acid during germination. The surface sediment contained similar to 105-106 inducible TFEs cm(-3). TFEs thus outnumber thermophilic sulfate-reducing endospores by an order of magnitude. The abundance of cultivable TFEs decreased exponentially with sediment depth with a half-life of 350 years. We estimate that 6 X 109 anaerobic thermophilic endospores are deposited on the seafloor per m2 per year in Aarhus Bay, and that these thermophiles represent >10% of the total endospore community in the surface sediment

Ion-exchange purification and structural characterization of five sulfated fucoidans from brown algae

Fucoidans are a diverse class of sulfated polysaccharides integral to the cell wall of brown algae, and due to their various bioactivities, they are potential drugs. Standardized work with fucoidans is required for structure-function studies, but remains challenging since available fucoidan preparations are often contaminated with other algal compounds. Additionally, fucoidans are structurally diverse depending on species and season, urging the need for standardized purification protocols. Here, we use ion-exchange chromatography to purify different fucoidans and found a high structural diversity between fucoidans. Ion-exchange chromatography efficiently removes the polysaccharides alginate and laminarin and other contaminants such as proteins and phlorotannins across a broad range of fucoidans from major brown algal orders including Ectocarpales, Laminariales and Fucales. By monomer composition, linkage analysis and NMR characterization, we identified galacturonic acid, glucuronic acid and O-acetylation as new structural features of certain fucoidans and provided a novel structure of fucoidan from Durvillaea potatorum with alpha-1,3-linked fucose backbone and beta-1,6 and beta-1,3 galactose branches. This study emphasizes the use of standardized ion-exchange chromatography to obtain defined fucoidans for subsequent molecular studies

Identifying Vessel Branching from Fluid Stresses on Microscopic Robots

Objects moving in fluids experience patterns of stress on their surfaces determined by the geometry of nearby boundaries. Flows at low Reynolds number, as occur in microscopic vessels such as capillaries in biological tissues, have relatively simple relations between stresses and nearby vessel geometry. Using these relations, this paper shows how a microscopic robot moving with such flows can use changes in stress on its surface to identify when it encounters vessel branches.Comment: Version 2 has minor clarification

Optics-less smart sensors and a possible mechanism of cutaneous vision in nature

Optics-less cutaneous (skin) vision is not rare among living organisms, though its mechanisms and capabilities have not been thoroughly investigated. This paper demonstrates, using methods from statistical parameter estimation theory and numerical simulations, that an array of bare sensors with a natural cosine-law angular sensitivity arranged on a flat or curved surface has the ability to perform imaging tasks without any optics at all. The working principle of this type of optics-less sensor and the model developed here for determining sensor performance may be used to shed light upon possible mechanisms and capabilities of cutaneous vision in nature