Biosynthesis of exopolysaccharide by a Bacillus licheniformis strain isolated from ropy cider

Listeria monocytogenes accumulates low molecular weight compounds (osmolytes, or compatible solutes) in response to chill stress. This response has been shown to be responsible, in part, for the chill tolerance of the species. Among the osmolytes tested to date, glycine betaine, gamma-butyrobetaine and carnitine display the strongest cryoprotective effect. These osmolytes are not synthesized in the cell and must be transported from the medium. In this study, the compatible solute accumulation profile of the food-borne pathogen L. monocytogenes was determined in balanced growth and stationary phase cultures grown in milk whey at 7 and 30 degrees C. In balanced growth cultures at 7 degrees C, glycine betaine (720 nmol/10(10) cfu) and carnitine (130 nmol/10(10) cfu) were the major osmolytes accumulated by wild-type L. monocytogenes 10403S, whereas carnitine (490 nmol/10(10) cfu) was the dominant osmolyte and glycine betaine was present in smaller amounts (270 nmol/10(10) cfu) in a mutant (L. monocytogenes LTG59) blocked in the major glycine betaine uptake system, glycine betaine porter II. In strain 10403S, glycine betaine and carnitine were present in eightfold and twofold excess at 7 degrees C compared to 30 degrees C; the respective ratios for strain LTG59 were 6 and 8. The intracellular concentration of osmolytes in stationary phase cultures at 7 degrees C was markedly reduced compared to that during balanced growth. Furthermore, at 4 degrees C, small but highly significant differences in growth were observed between strains. Strain LTG59 grew with a lag phase that was significantly longer, a generation time that was significantly greater and reached a final cell yield that was significantly lower than that of strain 10403S. The elevated accumulation of carnitine in the absence of glycine betaine porter II was insufficient to confer the magnitude of the cryoprotective effect displayed by the wild type.     

G-Quadruplex Formation in a Putative Coding Region of White Spot Syndrome Virus: Structural and Thermodynamic Aspects

White spot disease (WSD) is one of the most devastating viral infections of crustaceans caused by the white spot syndrome virus (WSSV). A conserved sequence WSSV131 in the DNA genome of WSSV was found to fold into a polymorphic G-quadruplex structure. Supported by two mutant sequences with single G→T substitutions in the third G₄ tract of WSSV131, circular dichroism and NMR spectroscopic analyses demonstrate folding of the wild-type sequence into a three-tetrad parallel topology comprising three propeller loops with a major 1 : 3 : 1 and a minor 1 : 2 : 2 loop length arrangement. A thermodynamic analysis of quadruplex formation by differential scanning calorimetry (DSC) indicates a thermodynamically more stable 1 : 3 : 1 loop isomer. DSC also revealed the formation of additional highly stable multimeric species with populations depending on potassium ion concentration.     

Nonswelling,Ultralow Content Inverse Electron‐Demand Diels–Alder Hyaluronan Hydrogels with Tunable Gelation Time: Synthesis and In Vitro Evaluation

Hyaluronan (HA) is a major component of the extracellular matrix and is particularly attractive for cell‐based assays; yet, common crosslinking strategies of HA hydrogels are not fully tunable and bioorthogonal, and result in gels subject to swelling, which affects their physicochemical properties. To overcome these limitations, HA hydrogels based on the inverse electron‐demand Diels–Alder (IEDDA) “click” reaction are designed. By crosslinking two modified HA components together, as opposed to using telechelic components, tunable gelation times as fast as 4.4 ± 0.4 min and as slow as 46.2 ± 1.8 min are achieved for facile use. By optimizing HA molar mass, ultralow polymer content hydrogels of 0.5% (w/v), resulting in minimal (<3–5% mass variation) to nonswelling (<1%), transparent and biodegradable hydrogels are synthesized. To demonstrate their versatility, the newly designed hydrogels are tested as matrices for 3D cell culture and retinal explant imaging where transparency is important. IEDDA hydrogels are cytocompatible with primary photoreceptors and enable multiphoton imaging of embedded retinal explants for double the time (>38 h) than agarose thermogels (<20 h). IEDDA HA hydrogels constitute a new hydrogel platform. They have low polymer content, tunable gelation time, and are stable, thereby making them suitable for a diversity of applications.     

Motion Estimation Based on Spline Interpolation in H.264/AVC Video Coder for Videoconferencing Application: Performance Versus Computation Load

The powerful H.264/AVC video coder involves a large encoding computational cost than the existing video standards due mainly to the motion-compensated estimation scheme based on a full search of multiple reference frames in the sequence. This strategy decreases the residual errors of the predicted frames and may improve the performance of the video coder. However a great number of computations are usually wasted without improving significantly the quality of the decoded video mostly in videoconferencing applications. To reduce the encoding computational load and preserve the performance of the video coder, this paper proposes to substitute the motion-compensated estimation method implemented in H.264/AVC by a temporal spline interpolation. Simulations on several test sequences show that important encoding saving times are achieved with a competitive quality of the decoded video compared to the exhaustive search of multiple reference frames in the H.264/AVC video coder.     

人脸图像超分辨率非线性学习算法

针对一般学习算法效率低下的问题,提出一种马尔可夫网络模型下的非线性学习算法。对输入的低分辨率图像以及训练用高分辨率图像和对应的低分辨率图像进行分块,并使图像基本对齐,构造训练图像集,利用训练集人脸图像的差异,采用块坐标限位操作技术,给出一种非线性样本搜索算法,降低搜索空间复杂度,提高了匹配效率和相关性。利用搜索到的高分辨率图像分块样本,直接输出超分辨率图像。分析和实验证实,与传统学习算法相比,该方法具有输出质量好、效率高的特点。     

Motion Estimation Algorithms Using the Deformation of Planar Hierarchical Mesh Grid for Videoconferencing Applications at Low Bit-rate Transmission

This paper studies the issue of reducing the temporal redundancy between consecutive frames of a videoconferencing sequence at low bit-rate transmission. To overcome the drawbacks of the traditional block matching algorithm implemented in the most current video coding standards, we propose to better describe the motion of objects through the deformation of planar rectangular mesh grid adapted to the edges of the moving objects in the scene. The traditional inter coding modes are then replaced by two new classes of encoding algorithms. The first one concerns the B-frames where the problem of motion estimation is solved by a bidirectional prediction algorithm which reconstructs the quadrilateral mesh grids without any coding cost. The second class of algorithm much more complex than the first one is specific to the P-frames based on the principle of merging two hierarchical grids of reference. This algorithm addresses not only the motion estimation problem based on the adaptive quadrilateral mesh grid but also the issue of the relevant information (e.g. the positions of the nodes, the connectivity of each quadrilateral mesh of the grid and the motion compensation) to efficiently encode. The implementation of these algorithms in a complete coding scheme offers good performance compared to the H.264/AVC video coder at low bit-rate transmission.