Reactivity difference between protolytic forms of some macrocyclic chromium(III) complexes in ligand substitution and electron transfer processes

The review provides insight into the mechanism of ligand substitution and electron transfer (from chromium(III) to iron(III)) by comparison of the reactivity of some tetraazamacrocyclic chromium(III) complexes in the conjugate acid-base forms. Use of two geometrical isomers made possible to estimate the influence of geometry and protolytic reactions in trans and cis position towards the leaving group on the rate enhancement. Studies on the reaction rates in different media demonstrated the role played by outer sphere interactions in a monodentate ligand substitution. (C) 2009 Published by Elsevier B.V.

OXIDATION OF CHLORIDE TO CHLORINE BY CERIC IONS MEDIATED BY THE 3 FORMS OF CRYSTALLINE CARBON

C-60 is more effective than graphite or diamond as a redox catalyst for the oxidation of chloride to chlorine by cerie ions.

BcsK(C) Is an Essential Protein for the Type VI Secretion System Activity in Burkholderia cenocepacia That Forms an Outer Membrane Complex with BcsL(B)

The type VI secretion system (T6SS) contributes to the virulence of Burkholderia cenocepacia, an opportunistic pathogen causing serious chronic infections in patients with cystic fibrosis. BcsK(C) is a highly conserved protein among the T6SSs in Gram-negative bacteria. Here, we show that BcsK(C) is required for Hcp secretion and cytoskeletal redistribution in macrophages upon bacterial infection. These two phenotypes are associated with a functional T6SS in B. cenocepacia. Experiments employing a bacterial two-hybrid system and pulldown assays demonstrated that BcsK(C) interacts with BcsL(B), another conserved T6SS component. Internal deletions within BcsK(C) revealed that its N-terminal domain is necessary and sufficient for interaction with BcsL(B). Fractionation experiments showed that BcsK(C) can be in the cytosol or tightly associated with the outer membrane and that BcsK(C) and BcsL(B) form a high molecular weight complex anchored to the outer membrane that requires BcsF(H) (a ClpV homolog) to be assembled. Together, our data show that BcsK(C)/BcsL(B) interaction is essential for the T6SS activity in B. cenocepacia.

Construction and biochemical characterization of recombinant cytoplasmic forms of the IucD protein (lysine:N6-hydroxylase) encoded by the pColV-K30 aerobactin gene cluster

The aerobactin gene cluster in pColV-K30 consists of five genes (iucABCD iutA); four of these (iucABCD) are involved in aerobactin biosynthesis, whereas the fifth one (iutA) encodes the ferriaerobactin outer membrane receptor. iucD encodes lysine:N6-hydroxylase, which catalyzes the first step in aerobactin biosynthesis. Regardless of the method used for cell rupture, we have consistently found that IucD remains membrane bound, and repeated efforts to achieve a purified and active soluble form of the enzyme have been unsuccessful. To circumvent this problem, we have constructed recombinant IucD proteins with modified amino termini by creating three in-frame gene fusions of IucD to the amino-terminal amino acids of the cytoplasmic enzyme beta-galactosidase. Two of these constructs resulted in the addition to the iucD coding region of a hydrophilic leader sequence of 13 and 30 amino acids. The other construct involved the deletion of the first 47 amino acids of the IucD amino terminus and the addition of 19 amino acids of the amino terminus of beta-galactosidase. Cells expressing any of the three recombinant IucD forms were found to produce soluble N6-hydroxylysine. One of these proteins, IucD439, was purified to homogeneity from the soluble fraction of the cell lysates, and it was capable of participating in the biosynthesis of aerobactin, as determined in vitro by a cell-free system and in vivo by a cross-feeding bioassay. A medium ionic strength of 0.25 (250 mM NaCl) or higher was required to maintain the protein in a catalytically functional, tetrameric state.(ABSTRACT TRUNCATED AT 250 WORDS)

Coprolites from the Cretaceous Bearpaw Formation of Saskatchewan

Coprolites from the Beechy Member of the Cretaceous Bearpaw Formation, southern Saskatchewan, presumably deposited by one or more species of mosasaur or large fish/shark, were recovered and analyzed using SEM/EDS. The data reveal the presence of pseudomorphous coccoid bacteria, potential filamentous bacteria, bacterial endospores and filamentous fungi. No recorded fossil plant or bone material could be identified, either within the highly compressed coprolitic mat-flattened full coprolite bolus - of recovered marine sediment encased in a mixed mat of hematite-apatite primary minerals heavily coated with Ca-smectite and nontronite, or the full coprolite bolus. The presence of fossil bacteria with morphological characteristics similar to those of endospores in other environments suggests that only robust microbial forms such as these survive diagenesis, partly with some carbon still intact, the remainder replaced with silica and iron. The data support the view that coprolites can serve as a useful source of information on the ancient microbial world. © 2012 Elsevier Ltd.