Inhibitory Effects of Artificial Sweeteners on Bacterial Quorum Sensing

Despite having been tagged as safe and beneficial, recent evidence remains inconclusive regarding the status of artificial sweeteners and their putative effects on gut microbiota. Gut microorganisms are essential for the normal metabolic functions of their host. These microorganisms communicate within their community and regulate group behaviors via a molecular system termed quorum sensing (QS). In the present study, we aimed to study the effects of artificial sweeteners on this bacterial communication system. Using biosensor assays, biophysical protein characterization methods, microscale thermophoresis, swarming motility assays, growth assays, as well as molecular docking, we show that aspartame, sucralose, and saccharin have significant inhibitory actions on the Gram-negative bacteria N-acyl homoserine lactone-based (AHL) communication system. Our studies indicate that these three artificial sweeteners are not bactericidal. Protein-ligand docking and interaction profiling, using LasR as a representative participating receptor for AHL, suggest that the artificial sweeteners bind to the ligand-binding pocket of the protein, possibly interfering with the proper housing of the native ligand and thus impeding protein folding. Our findings suggest that these artificial sweeteners may affect the balance of the gut microbial community via QS-inhibition. We, therefore, infer an effect of these artificial sweeteners on numerous molecular events that are at the core of intestinal microbial function, and by extension on the host metabolism.     

Cellophane for kidney dialysis

A new cellophane has been developed for use as a membrane in artificial kidney dialysis. Modification of the standard viscose casting and regeneration conditions produced films having permeabilities highly competitive with the cellulosic membranes presently employed in kidney dialysis. These modified cellophanes have permeabilities superior to the European cuprammonium films for all molecular species investigated. The greater permeabilities were found to be due to a much increased sweiling of these films resulting in a very small amount of cellulose which forms the barrier to molecular diffusion. These new cellophane structures also exhibit reasonable wet strength characteristics. The cellophane membranes offer the potential for obtaining a domestic membrane supply. This study indicates that although additional development work is required to produce a highly competitive membrane, these early results look extremely promising.     

Towards the Native Binding Modes of Antibiotics that Target Lipid II

The alarming rise of antimicrobial resistance (AMR) imposes severe burdens on healthcare systems and the economy worldwide, urgently calling for the development of new antibiotics. Antimicrobial peptides could be ideal templates for next-generation antibiotics, due to their low propensity to cause resistance. An especially promising branch of antimicrobial peptides target lipid II, the precursor of the bacterial peptidoglycan network. To develop these peptides into clinically applicable compounds, detailed information on their pharmacologically relevant modes of action is of critical importance. Here we review the binding modes of a selection of peptides that target lipid II and highlight shortcomings in our molecular understanding that, at least partly, relate to the widespread use of artificial membrane mimics for structural studies of membrane-active antibiotics. In particular, with the example of the antimicrobial peptide nisin, we showcase how the native cellular membrane environment can be critical for understanding of the physiologically relevant binding mode.     

Thermo-induced Vesicular Dynamics of Membranes Containing Cholesterol Derivatives

Membrane structural organization is an intrinsic property of a cell membrane. Any changes in lipid composition, and/or any stimuli that affect molecular packing induce structural re-organization. It membrane dynamics provide a means by which changes in structure organization can be determined, upon a change in the membrane internal or external environment. Here, we report on the effect of thermo-stress on membranes containing cholesterol liquid crystal (LC) compounds cholesterol benzoate (BENZO) and oxidized cholesterols. We have (1) revealed that lipid vesicles containing this artificial cholesterol derivative (BENZO) is thermo-responsive, and that this thermo-sensitivity is significantly similar to naturally oxy-cholesterols (2) elucidated the mechanism behind the membrane perturbation. Using Langmuir monolayer experiments, we have demonstrated that membrane perturbation was due to an increase in the molecular surface area, (3) discussed the similarities between cholesterol benzoate in the cholesterol LC state and in lipid bilayer membranes. Last, (4) drawing from previously reported findings, our new data on membrane dynamics, and the discussion above, we propose that artificial cholesterol derivatives such as BENZO, open new possibilities for controlled and tailored design using model membrane systems. Examples could include the development of membrane technology and provide a trigger for progress in thermo-tropical liquid crystal engineering.     

Solvent extraction using dialysis through artificial phase boundaries

Several solvent extraction systems were studied using a cellulose dialysis membrane as an artificial phase boundary separating one solvent phase from the other. Solutes were allowed to come to extraction equilibrium by permeation through the membrane. The rate of permeation depended on the osmotic properties of the solute, such as the molecular size and the presence of colloidal species. The extraction equilibrium was established by the solvent-extraction properties of the solute in each system, and the equilibrium was approached through the cellulose membrane by a first-order kinetic process. The method appears to be useful for ‘packaging’ organic solvents in membrane containers to be used for extractions in which time is not a factor. In certain cases, equally well extracted solutes, such as zirconium and aluminium 8-hydroxyquinolates, can be separated because one solute exists as a partially colloidal material [Zr(IV)] and hence does not pass through the membrane rapidly.     

Molecularly Imprinted Composite Membranes for Selective Detection of 2-Deoxyadenosine in Urine Samples

An important challenge for scientific research is the production of artificial systems able to mimic the recognition mechanisms occurring at the molecular level in living systems. A valid contribution in this direction resulted from the development of molecular imprinting. In this work, a novel molecularly imprinted polymer composite membrane (MIM) was synthesized and employed for the selective detection in urine samples of 2-deoxyadenosine (2-dA), an important tumoral marker. By thermal polymerization, the 2-dA-MIM was cross-linked on the surface of a polyvinylidene-difluoride (PVDF) membrane. By characterization techniques, the linking of the imprinted polymer on the surface of the membrane was found. Batch-wise guest binding experiments confirmed the absorption capacity of the synthesized membrane towards the template molecule. Subsequently, a time-course of 2-dA retention on membrane was performed and the best minimum time (30 min) to bind the molecule was established. HPLC analysis was also performed to carry out a rapid detection of target molecule in urine sample with a recovery capacity of 85%. The experiments indicated that the MIM was highly selective and can be used for revealing the presence of 2-dA in urine samples.     

试论人造香料的研发之路

论述了硝基麝香和多环麝香的研发简史、芳香族化合物的分子结构和香气之间的关系,以及Simmons-Smith反应在开发新香料中的应用,在此基础上探讨了人造香料的研究和开发之思路.     

Link between Lipid Second Messengers and Osmotic Stress in Plants

Plants are subject to different types of stress, which consequently affect their growth and development. They have developed mechanisms for recognizing and processing an extracellular signal. Second messengers are transient molecules that modulate the physiological responses in plant cells under stress conditions. In this sense, it has been shown in various plant models that membrane lipids are substrates for the generation of second lipid messengers such as phosphoinositide, phosphatidic acid, sphingolipids, and lysophospholipids. In recent years, research on lipid second messengers has been moving toward using genetic and molecular approaches to reveal the molecular setting in which these molecules act in response to osmotic stress. In this sense, these studies have established that second messengers can transiently recruit target proteins to the membrane and, therefore, affect protein conformation, activity, and gene expression. This review summarizes recent advances in responses related to the link between lipid second messengers and osmotic stress in plant cells.     

改性化合物对聚酰胺膜材料亲水性及抗污染性能影响的分子力学计算与实验研究

以反渗透技术应用于海水淡化为背景,采用分子力学方法计算聚酰胺反渗透膜材料PA及3种改性化合物(PEGMA,SPM,AMPS)与水分子、典型有机污染物海藻酸AA形成各种氢键复合物的相互作用能、生成几率与平均相互作用能,以此为基础选择适宜的膜改性化合物,增加膜表面亲水性,降低海藻酸污染。分子力学计算表明,PA及三种改性化合物与水分子结合的强弱顺序为：PEGMA＞PA＞SPM＞AMPS;它们与海藻酸AA分子结合的强弱顺序为：AMPS＞PA＞SPM＞PEGMA。将PEGA“链接”到聚酰胺膜SW30表面,制得改性聚酰胺膜MSW30。实验表明,改性聚酰胺膜MSW30的亲水性能及抗污染性能均较原膜SW30有显著提高,实验结果与分子力学计算结果一致。     

Influences of molecular weight, molecular size, flux, and recovery for aromatic pesticide removal by nanofiltration membranes

Eleven aromatic pesticides were used for a removal study using a 4040 spiral-wound polyamide nanofiltration (NF) membrane. The influences of molecular weight, molecular size (length and width), flux, and recovery were studied. The molecular weights of these pesticides are from 198 Da to 286 Da. Molecular sizes were determined by theoretical calculation for their length and width by “Hyperchem” based on their structures and orientation. Furthermore, the study held constant for two operated recoveries and fluxes to determine their effects. The results showed that the NF membrane can remove pesticides from 46% to 100% based on their molecular weights, lengths, fluxes and recoveries. The rejections were increased as the molecular weight increased, and a sharp increase to complete rejection (100%) was observed around MW 200 Da. Therefore, a molecular weight cut-off (MWC) of 200 Da can be determined for this membrane from this result. In addition, the results showed the molecular length was more significant than molecular width for these pesticides. The rejections were not only dependent on molecular weight and length, but also on operational flux and recovery. For a particular pesticide in the two operational fluxes and recoveries, the highest percent rejections occurred on high flux and low recovery, and lowest percent rejection occurred on low flux and high recovery, which would indicate the basic diffusion control theory.     

UNC119A Decreases the Membrane Binding of Myristoylated c‐Src

Plasma membrane localization of myristoylated c‐Src, a proto‐oncogene protein‐tyrosine kinase, is required for its signaling activity. Recent studies proposed that UNC119 protein functions as a solubilizing factor for myristoylated proteins, thereby regulating their subcellular distribution and signaling. The underlying molecular mechanism by which UNC119 regulates the membrane binding of c‐Src has remained elusive. By combining different biophysical techniques, we have found that binding of a myristoylated c‐Src‐derived N‐terminal peptide (Myr‐Src) by UNC119A results in a reduced membrane binding affinity of the peptide, due to the competition of binding to membranes. The dissociation of Myr‐Src from membranes is facilitated in the presence of UNC119A, as a consequence of which the clustering propensity of this peptide on the membrane is partially impaired. By these means, UNC119A is able to regulate c‐Src spatially in the cytoplasm and on cellular membranes, and this has important implications for its cellular signaling.     

PVC涂层膜材料老化研究进展

介绍了PVC涂层膜材料的光氧老化机理;系统地介绍了人工加速老化试验和自然老化试验方法及参照的国内外标准,并对材料老化后的测试方法做了介绍;最后分析了PVC膜材料在人工加速老化试验和自然老化试验下的相关性的研究现状及存在的问题。     

Antimicrobial Action of Water-Soluble β-Chitosan against Clinical Multi-Drug Resistant Bacteria

Recently, the number of patients infected by drug-resistant pathogenic microbes has increased remarkably worldwide, and a number of studies have reported new antibiotics from natural sources. Among them, chitosan, with a high molecular weight and α-conformation, exhibits potent antimicrobial activity, but useful applications as an antibiotic are limited by its cytotoxicity and insolubility at physiological pH. In the present study, the antibacterial activity of low molecular weight water-soluble (LMWS) α-chitosan (α1k, α5k, and α10k with molecular masses of 1, 5, and 10 kDa, respectively) and β-chitosan (β1k, β5k, and β10k) was compared using a range of pathogenic bacteria containing drug-resistant bacteria isolated from patients at different pH. Interestingly, β5k and β10k exhibited potent antibacterial activity, even at pH 7.4, whereas only α10k was effective at pH 7.4. The active target of β-chitosan is the bacterial membrane, where the leakage of calcein is induced in artificial PE/PG vesicles, bacterial mimetic membrane. Moreover, scanning electron microscopy showed that they caused significant morphological changes on the bacterial surfaces. An in vivo study utilizing a bacteria-infected mouse model found that LMWS β-chitosan could be used as a candidate in anti-infective or wound healing therapeutic applications.     

Deliver on Time or Pay the Fine: Scheduling in Membrane Trafficking

Membrane trafficking is all about time. Automation in such a biological process is crucial to ensure management and delivery of cellular cargoes with spatiotemporal precision. Shared molecular regulators and differential engagement of trafficking components improve robustness of molecular sorting. Sequential recruitment of low affinity protein complexes ensures directionality of the process and, concomitantly, serves as a kinetic proofreading mechanism to discriminate cargoes from the whole endocytosed material. This strategy helps cells to minimize losses and operating errors in membrane trafficking, thereby matching the appealed deadline. Here, we summarize the molecular pathways of molecular sorting, focusing on their timing and efficacy. We also highlight experimental procedures and genetic approaches to robustly probe these pathways, in order to guide mechanistic studies at the interface between biochemistry and quantitative biology.     

污水深度超滤过程的数学模拟及应用研究

以流体力学理论为基础，从膜结构的角度出发，以膜孔密度和膜孔径为主要参数建立了超滤膜过滤受污染水的膜结构参数模型，并以不同分子量分布的城市污水二级处理水为原水，对模型参数进行了拟合、验证。结果表明：膜结构参数模型能较好地反映深度处理污水的超滤膜污染过程。     

Stabilization of All-in-Water Emulsions To Form Capsules as Artificial Cells

Building artificial cells through a bottom-up approach is a remarkable challenge that would be of interest for our understanding of the origin of life, research into the minimal conditions required for life, the formation of bioreactors, and for industrial applications. To date, capsules such as liposomes, including polymersomes, are widely used, but the low membrane permeability and method to encapsulate biological materials within these structures hamper their use. By contrast, all-in-water emulsion droplets, including coacervate droplets, are promising compartments, mainly because they can spontaneously sequester chemicals. However, they lack a membrane necessary to control exchange between the inner and outer media. Moreover, droplets tend to coalesce with time, yielding macroscopic phase separation that is deleterious for any use as artificial cells. Recent advances, which are reviewed herein, have shown that such droplets can be stabilized by using lipid membranes, liposomes, polymers, proteins, and particles, and thus, preventing coalescence. Finally, different strategies that could allow the future development of artificial cells from these stabilized all-in-water emulsion droplets are discussed.     

Thermotropic and Barotropic Phase Behavior of Phosphatidylcholine Bilayers

Bilayers formed by phospholipids are frequently used as model biological membranes in various life science studies. A characteristic feature of phospholipid bilayers is to undergo a structural change called a phase transition in response to environmental changes of their surroundings. In this review, we focus our attention on phase transitions of some major phospholipids contained in biological membranes, phosphatidylcholines (PCs), depending on temperature and pressure. Bilayers of dipalmitoylphosphatidylcholine (DPPC), which is the most representative lipid in model membrane studies, will first be explained. Then, the bilayer phase behavior of various kinds of PCs with different molecular structures is revealed from the temperature–pressure phase diagrams, and the difference in phase stability among these PC bilayers is discussed in connection with the molecular structure of the PC molecules. Furthermore, the solvent effect on the phase behavior is also described briefly.     

Positive roles of biofilm during the operation of membrane bioreactor for water reuse

Generally, membrane biofilm have been believed to be minimized during the operation of membrane bioreactor (MBR) for wastewater treatment and reuse. In this study, positive roles of membrane biofilm in the intermittently aerated MBR system were highlighted. During the long-term operation using real domestic wastewater, membrane biofilm played secondary filtration barrier for both low and high molecular weight organic matters. The biofilm on the membrane surface was responsible for the removal of low molecular weight organic matters by the use of easily degradable organic matters (i.e. <1 kDa) as microbial carbon and energy sources during the filtration. Also, track study showed that the significant denitrification took place by the membrane biofilm, proved by the degradation of carbon source and increase of alkalinity such as inorganic carbon. Nevertheless the necessity of further study, this study will give unique insight into positive roles of membrane biofilm, and also continue to aid both fundamental studies and developments of MBR processes.