No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Resistance to tetracycline (Tc), an inhibitor of protein synthesis, decreases its effectiveness for the treatment of bacterial infections. Tc resistance (TcR) can be mediated by the ribosomal protection protein, Tet(O), which was first reported in Campylobacter jejuni, a cause of bacterial diarrhea worldwide. Tet(O) confers TcR by mediating Tc release from 70S ribosomes, thus restoring protein synthesis. Tet(O) is widely distributed in a variety of bacterial genera, restraining the clinical use of Tc. This thesis is the first investigation into the role of the conserved set of amino acid residues, YSPVST, occupying positions 507-512 at the tip of domain IV of Tet(O). Impaired Tc release from 70S ribosomes observed with Tet(O)mutants lacking one or more of these conserved residues suggests residues at positions 509-512 play a role in Tet(O)-mediated TcR. This study provides insight into the molecular mechanism of TcR, which is essential for the development of novel therapeutics.

In the present study, the corrosion behaviour of several magnesia-chrome (MC) and magnesia-alumina spinel (MA) bricks against fayalite type slags was investigated and the role of the spinel phases was highlighted . The experimental results revealed that the corrosion resistance of the MC bricks was superior to the MA bricks against KIVCET slags in static and dynamic conditions . As a result of the interaction between MgO from MC bricks and the slag, a modified forsterite phase (Mg, Fe, Zn, Ca)₂SiO₄ was formed, which destroyed the precipitated complex spinel bonds at the grain boundaries of periclase and magnesia-chromia spinel . Furthermore, both MgO and MgO-MgAl₂O₄ spinel in the MA brick dissolved into the slag, which resulted in modified forsterite phases of (Mg, Fe, Zn, Ca)₂SiO₄ and (Mg, Fe, Zn)(Fe, Al)₂O₄ complex spinels, respectively. In addition, the accretion formation in the KIVCET furnace was investigated through solubility experiments of Cr₂0₃ in the KIVCET slag with various amounts of lead, which revealed that the net contribution of Cr₂0₃ to the spinel formation is the highest in the barren (no Pb) slag, followed by high-lead (11% Pb) and it is the lowest for the low-lead (6% Pb) slag. The amount of spinel solid solution increased consistently with increasing Cr₂0₃ dissolved and the PbO existent in the slag. From examinations of several used bricks from the tuyere area of a Peirce Smith nickel converter, it was found that the corrosion is due to the interaction of the partially oxidized matte penetrating deep into the brick and the magnesia grains forming (Mg, Fe, Ni, Co) xOy spinels . Analyses of brick samples used in the KIVCET Electric Furnace roof identified deep reaching sulphation, which weakened the bonding phase between coarse magnesia grains. In the Bottom Blown Oxygen Converter, a highly aggressive lead and bismuth oxide rich slag penetrated deep into the brick, which destroyed the grain boundaries, causing the refractory to be easily eroded at the refractory-slag interface. Our studies concluded that the spinel phases, either as magnesium chromate, magnesium aluminate or complex spinel [(Mg, Fe)(Cr, Al, Fe)₂O₄], enhanced the corrosion resistance of a basic refractory to fayalite type slags from the non-ferrous smelting and converting furnaces.