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Abstract: Bacteria are abundant in many natural and engineered environments where they are thought to exert important controls on the cycling, mobility, bioavailability, and toxicity of metal contaminants. In order to probe their role in moderating the behavior of lanthanides, pH-dependent adsorption edges of 13 individual lanthanides and yttrium to the Gram-negative bacterium Pantoea agglomerans were used to generate discrete site surface complexation constants. The calculated surface complexation constants were compared with stability constants estimated using linear free energy relationships based on a number of hydroxyl-containing ligands. The experimental data suggests that lanthanide adsorption edges below pH 6.5 are consistent with adsorption to phosphate groups for the light and some of the middle lanthanides (La to Gd), whereas some of the middle and heavy lanthanides appear to favor carboxyl co-ordination (Tb to Yb), although exceptions occur in each grouping. The experimentally derived surface complexation constants for carboxyl coordination were of similar magnitude to stability constants estimated from linear free energy correlations using fulvic acid stability constants. The implication is that the adsorption of lanthanides to bacterial surfaces could be modeled reasonably well using lanthanide stability constants for natural organic matter, except perhaps at low pH where phosphate binding dominates.

Open Access

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Abstract: The transient complex between cytochrome f and plastocyanin from the cyanobacterium Nostoc sp. PCC 7119 has been analysed by X-ray Absorption Spectroscopy in solution, using both proteins in their oxidized and reduced states. Fe K-edge data mainly shows that the atypical metal coordination geometry of cytochrome f, in which the N-terminal amino acid acts as an axial ligand of the heme group, remains unaltered upon binding to its redox partner, plastocyanin. This fact suggests that cytochrome f provides a stable binding site for plastocyanin and minimizes the reorganization energy required in the transient complex formation, which could facilitate the electron transfer between the two redox partners.

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Abstract: For the initiation of DNA replication, dsDNA is unwound by helicases. Primases then recognize specific sequences on the template DNA strands and synthesize complementary oligonucleotide primers that are elongated by DNA polymerases in leading- and lagging-strand mode. The bacterial plasmid RSF1010 provides a model for the initiation of DNA replication, because it encodes the smallest known primase RepB? (35.9 kDa), features only 1 single-stranded primase initiation site on each strand (ssiA and ssiB, each 40 nt long with 5?- and 3?-terminal 6 and 13 single-stranded nucleotides, respectively, and nucleotides 7–27 forming a hairpin), and is replicated exclusively in leading strand mode. We present the crystal structure of full-length dumbbell-shaped RepB? consisting of an N-terminal catalytic domain separated by a long ?-helix and tether from the C-terminal helix-bundle domain and the structure of the catalytic domain in a specific complex with the 6 5?-terminal single-stranded nucleotides and the C7–G27 base pair of ssiA, its single-stranded 3?-terminus being deleted. The catalytic domains of RepB? and the archaeal/eukaryotic family of Pri-type primases share a common fold with conserved catalytic amino acids, but RepB? lacks the zinc-binding motif typical of the Pri-type primases. According to complementation studies the catalytic domain shows primase activity only in the presence of the helix-bundle domain. Primases that are highly homologous to RepB? are encoded by broad-host-range IncQ and IncQ-like plasmids that share primase initiation sites ssiA and ssiB and high sequence identity with RSF1010.

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Abstract: We report a thermodynamic investigation of the adsorption of saturated and unsaturated (cis- and trans-) alkyl amides onto the surface of graphite from their pure liquids and from binary mixtures. We identify the formation of solid monolayers of the amides at temperatures when the bulk materials are liquid. The extent of this presolidification is much more extensive than other related materials, indicating that these amide layers are significantly more stable. The monolayer stability is found to be greatest for saturated amides. In addition, the stability of unsaturated amides is extremely sensitive to the location of the double bonds in the alkyl chain of the molecules, and trans isomers are found to be more stable than cis. We also address the preferential adsorption and mixing behavior of amide mixtures and amides mixed with other species coadsorbed onto graphite from binary solution. The results indicate that the amide molecules appear to be adsorbed with their principal axis parallel to the graphite surface and that amides are found to be strongly preferentially adsorbed with respect to alkanes. Interestingly the amides appear to mix rather better than might have been expected. There is also evidence of a number of other transitions in the adsorbates.

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Abstract: We present the design of a synchrotron x-ray beamline (BL-I11) dedicated to powder diffraction experiments, currently under construction at Diamond Light Source (DLS). An in-vaCLIurn Lindulator will provide an intense and highly collimated x-ray Source and with the necessary optics, a high purity beam of low energy-bandpass x-rays in the range 5-30 keV will be delivered at the sample. The diffraction instrument is designed to have the flexibility to house a variety of sample environments and to have two detection systems to collect high quality diffraction data, i.e. multi-analysing crystals for high angular resolution experiments and a fast position sensitive detector for tirne-resolved studies. BL-I11 will be a powerful state-of-the-art dedicated user facility for high resolution (d-space and time) powder diffraction studies of polycrystalline materials under ambient and non-ambient conditions.