University of Hohenheim

About: University of Hohenheim is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Population & Soil water. The organization has 8585 authors who have published 16406 publications receiving 567377 citations.

Regulation and function of ammonium carriers in bacteria, fungi, and plants

Abstract: The ammonium transport (Amt) family of proteins comprises a unique and ubiquitous group of integral membrane proteins found in all domains of life. They are present in bacteria, archaea, fungi, plants, and animals, including humans where they are represented by the Rhesus proteins. The Amt proteins have a variety of functions. In bacteria and fungi, they act to scavenge ammonium and to recapture ammonium lost from cells by diffusion across the cell membrane. In fungi, they have also been proposed to act as ammonium sensors to control filamentous growth. In plants, they make a major contribution to nitrogen nutrition and in higher animals; they are involved in ammonium fluxes in kidney and liver. In this paper, we review current knowledge of the biology of Amt proteins in bacteria, fungi, and plants with particular attention to the different functions of the proteins and their modes of regulation.

Influence of droplet size on the efficacy of oil-in-water emulsions loaded with phenolic antimicrobials

Abstract: In this study we investigated the effect of droplet size on the antimicrobial activity of emulsions containing two essential oil compounds that are known for their antimicrobial effectiveness: carvacrol and eugenol. Coarse emulsions were prepared by blending a triacylglyceride (Miglyol 812N) containing various concentrations of carvacrol or eugenol (5, 15, 30, 50 wt%) at an oil droplet mass fraction of 10 wt% with an aqueous phase containing 2 wt% Tween 80®. Premixes were then further dispersed using a high shear blender, a high pressure homogenizer at different pressures or an ultrasonicator to produce droplets with a variety of mean diameters. Microscopy and light scattering storage stability studies over 10 days indicated that manufactured emulsions were stable, i.e. that no aggregation, creaming or other destabilization mechanisms occurred and droplet size distributions remained unchanged. The antimicrobial activity of emulsions was assessed against two model microorganisms, the Gram negative Escherichia coli C 600 and the Gram positive Listeria innocua, by determining growth over time behavior. The analysis yielded the unexpected result that emulsions with larger droplet sizes were more effective at inhibiting growth and inactivating cells than smaller ones. For example, emulsions with a mean oil droplet size of 3000 nm at a concentration of 800 ppm carvacrol completely inhibited L. innocua, while for 80 nm emulsions, only a delay of growth could be observed. Measurements of the concentration of the antimicrobial compounds in the aqueous phase indicated that concentrations of eugenol and carvacrol decreased with decreasing oil droplet sizes. Determination of interfacial tension further showed that eugenol and carvacrol are preferentially located in the oil–water interfaces. Theoretical calculations of Tween 80® concentrations needed to saturate interfaces suggested that in small emulsions for the given formulation less Tween 80® micelles are present in the aqueous phase. We therefore attribute the fact that antimicrobial nanoemulsions are less active than macroemulsions due to an increased sequestering of antimicrobials in emulsion interfaces and a decreased solubilization in excess Tween 80® micelles.

Error estimates for scattered data interpolation on spheres

Abstract: We study Sobolev type estimates for the approximation order resulting from using strictly positive definite kernels to do interpolation on the n-sphere. The interpolation knots are scattered. Our approach partly follows the general theory of Golomb and Weinberger and related estimates. These error estimates are then based on series expansions of smooth functions in terms of spherical harmonics. The Markov inequality for spherical harmonics is essential to our analysis and is used in order to find lower bounds for certain sampling operators on spaces of spherical harmonics.