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Background Salmonella, a foodborne pathogen, possesses a type I-E clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated (Cas) system. We investigated the system's role in regulating Salmonella virulence by deleting the CRISPR arrays and Cas operon. Results Our study demonstrates invasion and proliferation defects of CRISPR-Cas knockout strains in intestinal epithelial cells and macrophages owing to the repression of invasion and virulence genes. However, proliferation defects were not observed in the Gp91.sup.phox-/- macrophages, suggesting the system's role in the pathogens' antioxidant defense. We deduced that the CRISPR-Cas system positively regulates H.sub.2O.sub.2 importer (OmpW), catalase (katG), peroxidase (ahpC), and superoxide dismutase (soda and sodCI), thereby protecting the cells from oxidative radicals. The knockout strains were attenuated in in-vivo infection models (Caenorhabditis elegans and BALB/c mice) due to hypersensitivity against antimicrobial peptides, complement proteins, and oxidative stress. The attenuation in virulence was attributed to the suppression of LPS modifying (pmr) genes, antioxidant genes, master regulators, and effectors of the SPI-1 (invasion) and SPI-2 (proliferation) islands in knockout strains. The regulation could be attributed to the partial complementarity of the CRISPR spacers with these genes. Conclusions Overall, our study extends our understanding of the role of the CRISPR-Cas system in Salmonella pathogenesis and its virulence determinants. Keywords: Salmonella, Type 1-E CRISPR-Cas system, Virulence, SPI-1-T3SS, SPI-2-T3SS, Anti-oxidant genes, Author(s): Nandita Sharma[sup.1], Ankita Das[sup.1], Abhilash Vijay Nair[sup.2], Palash Sethi[sup.1], Vidya Devi Negi[sup.3], Dipshikha Chakravortty[sup.2] and Sandhya Amol Marathe[sup.1] Introduction The bacterial adaptive immune system, Clustered Regularly Interspaced Short Palindromic [...]

We employ polymer integral equation theory to study a simplified model of semiflexible polymerized ionic liquids (PolyILs) that interact via hard core repulsions and short range screened Coulomb interactions. The multi-scale structure in real and Fourier space of PolyILs (ions chosen to mimic Li, Na, K, Br, PF6, and TFSI) are determined as a function of melt density, Coulomb interaction strength, and ion size. Comparisons with a homopolymer melt, a neutral polymer–solvent-like athermal mixture, and an atomic ionic liquid are carried out to elucidate the distinct manner that ions mediate changes of polymer packing, the role of excluded volume effects, and the influence of chain connectivity, respectively. The effect of Coulomb strength depends in a rich manner on ion size and density, reflecting the interplay of steric packing, ion adsorption, and charge layering. Ion-mediated bridging of monomers is found, which intensifies for larger ions. Intermediate range charge layering correlations are characterized by a many-body screening length that grows with PolyIL density, cooling, and Coulomb strength, in disagreement with Debye–Hückel theory, but in accord with experiments. Qualitative differences in the collective structure, including an ion-size-dependent bifurcation of the polymer structure factor peak and pair correlation function, are predicted. The monomer cage order parameter increases significantly, but its collective ion counterpart decreases, as ions become smaller. Such behaviors allow one to categorize PolyILs into two broad classes of small and large ions. Dynamical implications of the predicted structural results are qualitatively discussed. [ABSTRACT FROM AUTHOR]

Relativistic effects are important to understand the chemistry of heavier elements across the periodic table (PT). Three important relativistic effects are: contraction of s- and p-orbitals (direct relativistic effect), expansion of d- and f-orbitals (indirect relativistic effect) and spin–orbit (SO) coupling to split the p-, d- and f-orbitals. Each of these effects is approximately proportional to Z 2 (Z = atomic number) for the valence shell electrons in many electron atoms and consequently, these relativistic effects dominantly control the properties of the heavier elements (mainly the 6th and 7th period elements). These aspects are not given the proper importance in most of the inorganic chemistry text books and in chemistry education at the university level.

Man-made activities can release the ozone depleting substances (ODSs) like chlorofluorocarbons (CFCs) and other halocarbons stable in atmosphere and ultimately, they migrate to the stratosphere where they can destroy the ozone layer through the XOx catalytic cycle (X = Cl, Br). The active forms in this catalytic cycle are X and XO that can be arrested in the inactive forms like XONO2 (halogen nitrate, an additive compound of two odd electron molecules XO and NO2) and HX (produced in the reaction of X with CH4) in the stratosphere to prevent the ozone depletion cycle. The catalytically active forms from these inactive species can be regenerated in the reactions on heterogeneous solid surface like polar stratospheric cloud (specially Type II PSC formed at about −85 °C). Formation of such PSC in the stratosphere is only possible in the supercooled stable Antarctic vortex produced in the prolonged winter. In fact, formation of such PSC in the stratosphere is not possible in the other regions of the earth and not even in the Arctic pole where no stable Arctic vortex is generally formed in the winter. Thus nature confines the ozone depletion reactions mainly in the stratosphere of Antarctica pole which is practically inhabited.