University of Konstanz

About: University of Konstanz is a education organization based out in Konstanz, Baden-Württemberg, Germany. It is known for research contribution in the topics: Population & Visualization. The organization has 12115 authors who have published 27401 publications receiving 951162 citations. The organization is also known as: University of Constance & Universität Konstanz.

Kinetics of CH4 oxidation in oxic soils exposed to ambient air or high CH4 mixing ratios

Abstract: The kinetic parameters of CH4 oxidation (Km, Vmax, apparent threshold = Tha) were measured using different oxic soils (cultivated cambisol, forest luvisol, meadow cambisol, paddy soil) both in a fresh state and after 3 weeks preincubation under high CH4 mixing ratios (20%). The preincubation resulted in an increase of the most probable number of methanotrophic bacteria. In fresh soils, CH4 oxidation followed Michaelis-Menten kinetics with a low Km (30–51 nM CH4), low Vmax (0.7–3.6 nmol CH4 h−1g−1dw soil), and low Tha (0.2–2.7 ppmv CH4). In preincubated soils, CH4 oxidation exhibited biphasic kinetics in which two different CH4 saturation curves were apparently superimposed on each other. Eadie-Hofstee plots of the data showed two activities with different kinetic parameters: a high-affinity activity with low Km (13–470 nM CH4), low Vmax (2.1–150.0 nmol CH4 h−1g−1dw) and low Tha (0.3–4.1 ppmv CH4) being similar to the kinetic parameters in fresh soils; and a low-affinity activity with high Km (1740–27 900 nM CH4), high Vmax (270–3 690 nmol CH4 h−1g−1dw) and high Tha (11–45 ppmv CH4) being similar to the kinetic parameters known from methanotrophic bacteria. The low-affinity activity was also observed in a soil over a deep natural gas source which was permanently exposed to high CH4 mizing ratios (>5% CH4). Bacteria culturable as methanotrophs are probably responsible for the low-affinity activity which is typical for the soils exposed to high CH4 mixing ratios. However, the bacteria responsible for the high-affinity activity are still unknown. This activity is typical for the soils exposed to only ambient CH4 mixing ratios. Both high- and low-affinity activities were inhibited by autoclaving and by acetylene.

In situ detection of heavy metal substituted chlorophylls in water plants

Abstract: The in vivo substitution of magnesium, the central atom of chlorophyll, by heavy metals (mercury, copper, cadmium, nickel, zinc, lead) leads to a breakdown in photosynthesis and is an important damage mechanism in heavy metal-stressed plants In this study, a number of methods are presented for the efficient in situ detection of this substitution (ie in whole plants or in chloroplasts) While macroscopic observations point to the formation of heavy metal chlorophylls at higher concentrations, fluorescence microscopy enables the detection of this reaction at very low substitution rates Therefore, the course of the reaction can be followed by continuously measuring the fluorescence of whole plants Furthermore absorbance spectroscopy of whole cells or isolated chloroplasts also enables the in situ detection of heavy metal chlorophylls These methods provide practicable approaches in detecting the formation of these compounds in situ, avoiding artefacts that might occur using extraction methods based on polar solvents In addition to the new methods for in situ detection, an extreme heterogeneity in the reaction of cells in the same tissue upon heavy metal stress was observed: while some cells are already disintegrating, others still show normal fluorescence and photosynthetic activity Measurements of fluorescence kinetics gave a further hint that in high light intensity a substitution of Mg by heavy metals might take place specifically in PS II reaction centres

Calcium Carbonate Polyamorphism and Its Role in Biomineralization : How Many Amorphous Calcium Carbonates Are There?

Abstract: Although the polymorphism of calcium carbonate is well known, and its polymorphs--calcite, aragonite, and vaterite--have been highly studied in the context of biomineralization, polyamorphism is a much more recently discovered phenomenon, and the existence of more than one amorphous phase of calcium carbonate in biominerals has only very recently been understood. Here we summarize what is known about polyamorphism in calcium carbonate as well as what is understood about the role of amorphous calcium carbonate in biominerals. We show that consideration of the amorphous forms of calcium carbonate within the physical notion of polyamorphism leads to new insights when it comes to the mechanisms by which polymorphic structures can evolve in the first place. This not only has implications for our understanding of biomineralization, but also of the means by which crystallization may be controlled in medical, pharmaceutical, and industrial contexts.