Identification and characterization of a glucan-producing enzyme from Lactobacillus hilgardii TMW 1.828 involved in granule formation of water kefir

Water kefir is a home made fermented beverage based on a sucrose solution with fruit extracts. The inoculum of such fermentations consists of macroscopic granula containing lactic and acetic acid bacteria, and yeasts, which are embedded in an exopolysaccharide (EPS) matrix. In this work, a strain of Lactobacillus hilgardii producing large amounts of the granule-forming dextran could be isolated. The glycosyltransferans (Gtf) commonly called glucansucrase responsible for the production of this dextran was purified from L. hilgardii. Characteristic enzyme kinetic data were obtained. Optimum activity was observed between pH 4.3 and 4.6 and temperatures between 40 °C and 45 °C. A Michaelis–Menten kinetic could be fit to the experimental data and a K_M of 0.0385 M was calculated. The corresponding gtf gene was identified and characterized. It encodes a 1448 amino acid protein with higher homologies to Gtfs of Lactobacillus parabuchneri, Lactobacillus sakei and Lactobacillus fermentum followed by lower homologies to Lactobacillus reuteri Gtfs. By knockout experiments the role of this gene in granule dextran production was demonstrated.     

On Floating‐Point Normal Vectors

In this paper we analyze normal vector representations. We derive the error of the most widely used representation, namely 3D floating‐point normal vectors. Based on this analysis, we show that, in theory, the discretization error inherent to single precision floating‐point normals can be achieved by 2^50.2 uniformly distributed normals, addressable by 51 bits. We review common sphere parameterizations and show that octahedron normal vectors perform best: they are fast and stable to compute, have a controllable error, and require only 1 bit more than the theoretical optimal discretization with the same error.     

Investigation of the Gas‐Liquid Flow in a Stopper‐Rod Controlled SEN

The behaviour of two‐phase gas‐liquid flows in a stopper‐rod controlled submerged entry nozzle (SEN) is investigated in water model experiments. The observed two‐phase flow patterns can be classified into either bubble coring or bubbly slug. The scaling of the two‐phase flows by means of similarity parameters is discussed. In the experiments, it is found that the liquid flow rates depend strongly on the two‐phase flow patterns. Additionally, the influence of swirl on the flow patterns is investigated in detail. It is shown that swirl has a marked impact on the transition from bubble coring to bubbly slug. Finally, an estimation of the two‐phase argon‐steel flow patterns in industrialscale SEN flows is given.     

Analysis of spatial arrangement of particles in thin foil of Al-Al4C3 material

TEM images of thin foils with quasi-globular particles are examined by means of two methods of spatial statistics. The spatial arrangement of particle reference points is described by means of quadrat count statistics and by polygonal method (the analysis of the Voronoi mosaic generated by patterns of particle reference points). A good agreement between the both approaches is found, the polygonal method is more sensitive and its results are more conclusive.