Weizmann Institute of Science

About: Weizmann Institute of Science is a education organization based out in Rehovot, Israel. It is known for research contribution in the topics: Population & Gene. The organization has 21942 authors who have published 54561 publications receiving 3032812 citations. The organization is also known as: Bessie F. Lawrence International Summer Science Institute & Weitzman Institute.

Bacterial Adherence to Cell Surface Sugars

Abstract: Bacterial adherence to animal cell surfaces is of interest because of its relation to pathogenicity and the insight it provides into determinants of intercellular recognition. The attachment of various strains of Escherichia coli and Salmonella spp. to epithelial cells and phagocytes is inhibited by D-mannose, and the adherence of other bacteria is inhibited by sugars such as L-fucose and D-galactose, suggesting that sugar-mediated adherence is widespread. This intercellular recognition is thought to be mediated by sugar residues (e.g. D-mannose) on the surface of animal cells, to which bacteria attach by a sugar-binding substance on their surface. The nature of the receptors on the animal cells is unknown. There is evidence that E. coli produces lectin-like substances specific for D-mannose, by which it binds to the cells. The most common form of these lectin-like substances appears to be the bacterial pili, which can be reversibly dissociated into their protein subunits. The lectin can also be in the form of bacterial flagella or tightly attached to the outer membrane of the bacteria. Mannose-specific attachment may assist bacteria in colonizing and invading their hosts: methyl alpha-D-mannoside (but not methyl alpha-D-glucoside) significantly reduced infection of the urinary tract of mice by virulent strains of E. coli. Once bacteria penetrate the host their ability to binding sugars on phagocytes may impair their virulence by facilitating phagocytosis. Further studies of the sugar-mediated bacterial adherence by organisms growing in vivo and the structural identification of the host cell receptors may lead to the design of more effective adherence inhibitors that may help to prevent certain bacterial infections.

Dynamic changes in optical and chemical properties of tar ball aerosols by atmospheric photochemical aging

Abstract: Following wood pyrolysis, tar ball aerosols were laboratory generated from wood tar separated into polar and nonpolar phases Chemical information of fresh tar balls was obtained from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and single-particle laser desorption/resonance enhanced multiphoton ionization mass spectrometry (SP-LD-REMPI-MS) Their continuous refractive index (RI) between 365 and 425 nm was retrieved using a broadband cavity enhanced spectroscopy (BBCES) Dynamic changes in the optical and chemical properties for the nonpolar tar ball aerosols in NOx -dependent photochemical process were investigated in an oxidation flow reactor (OFR) Distinct differences in the chemical composition of the fresh polar and nonpolar tar aerosols were identified Nonpolar tar aerosols contain predominantly high-molecular weight unsubstituted and alkyl-substituted polycylic aromatic hydrocarbons (PAHs), while polar tar aerosols consist of a high number of oxidized aromatic substances (eg, methoxy-phenols, benzenediol) with higher O : C ratios and carbon oxidation states Fresh tar balls have light absorption characteristics similar to atmospheric brown carbon (BrC) aerosol with higher absorption efficiency towards the UV wavelengths The average retrieved RI is 1661+0020i and 1635+0003i for the nonpolar and polar tar aerosols, respectively, with an absorption Angstrom exponent (AAE) between 57 and 78 in the detected wavelength range The RI fits a volume mixing rule for internally mixed nonpolar/polar tar balls The RI of the tar ball aerosols decreased with increasing wavelength under photochemical oxidation Photolysis by UV light (254 nm), without strong oxidants in the system, slightly decreased the RI and increased the oxidation state of the tar balls Oxidation under varying OH exposure levels and in the absence of NOx diminished the absorption (bleaching) and increased the O : C ratio of the tar balls The photobleaching via OH radical initiated oxidation is mainly attributed to decomposition of chromophoric aromatics, nitrogen-containing organics, and high-molecular weight components in the aged particles Photolysis of nitrous oxide ( N2O ) was used to simulate NOx -dependent photochemical aging of tar balls in the OFR Under high- NOx conditions with similar OH exposure, photochemical aging led to the formation of organic nitrates, and increased both oxidation degree and light absorption for the aged tar ball aerosols These observations suggest that secondary organic nitrate formation counteracts the bleaching by OH radical photooxidation to eventually regain some absorption of the aged tar ball aerosols The atmospheric implication and climate effects from tar balls upon various oxidation processes are briefly discussed

A global transcriptional switch between the attack and growth forms of Bdellovibrio bacteriovorus.

Abstract: Bdellovibrio bacteriovorus is an obligate predator of bacteria ubiquitously found in the environment. Its life cycle is composed of two essential phases: a free-living, non-replicative, fast swimming attack phase (AP) wherein the predator searches for prey; and a non-motile, actively dividing growth phase (GP) in which it consumes the prey. The molecular regulatory mechanisms governing the switch between AP and GP are largely unknown. We used RNA-seq to generate a single-base-resolution map of the Bdellovibrio transcriptome in AP and GP, revealing a specific "AP" transcriptional program, which is largely mutually exclusive of the GP program. Based on the expression map, most genes in the Bdellovibrio genome are classified as "AP only" or "GP only". We experimentally generated a genome-wide map of 140 AP promoters, controlling the majority of AP-specific genes. This revealed a common sigma-like DNA binding site highly similar to the E. coli flagellar genes regulator sigma28 (FliA). Further analyses suggest that FliA has evolved to become a global AP regulator in Bdellovibrio. Our results also reveal a non-coding RNA that is massively expressed in AP. This ncRNA contains a c-di-GMP riboswitch. We suggest it functions as an intracellular reservoir for c-di-GMP, playing a role in the rapid switch from AP to GP.