Investigating the persistence of tick-borne pathogens via the R-0 model

In the epidemiology of infectious diseases, the basic reproduction number, R-0, has a number of important applications, most notably it can be used to predict whether a pathogen is likely to become established, or persist, in a given area. We used the R-0 model to investigate the persistence of 3 tick-borne pathogens; Babesia microti, Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato in an Apodemus sylvaticus-Ixodes ricinus system. The persistence of these pathogens was also determined empirically by screening questing ticks and wood mice by PCR. All 3 pathogens behaved differently in response to changes in the proportion of transmission hosts on which I. ricinus fed, the efficiency of transmission between the host and ticks and the abundance of larval and nymphal ticks found on small mammals. Empirical data supported theoretical predictions of the R-0 model. The transmission pathway employed and the duration of systemic infection were also identified as important factors responsible for establishment or persistence of tick-borne pathogens in a given tick-host system. The current study demonstrates how the R-0 model can be put to practical use to investigate factors affecting tick-borne pathogen persistence, which has important implications for animal and human health worldwide.

Late-Holocene marine radiocarbon reservoir correction (Delta R) for the west coast of South Africa

In order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or Delta R value. This study measured the Delta R on both known-age pre-bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of South Africa: the southwestern Cape and Namaqualand. Pooling the data by region produces Delta R values that are similar enough to use a west coast weighted mean Delta R of 146 +/- 85 C-14 years to correctly calibrate marine shell or mixed marine and terrestrial C-14 ages. There are however temporal differences in Delta R throughout the Holocene, which we compare with proxy data for upwelling and sea surface temperatures.

Catalysing open innovation through publicly funded R&D: A Comparison of University and Company-based research centres

Public funding of university and company-based R&D centres of excellence is widespread both in core and more peripheral regions. What is less well-known is whether these R&D centres can catalyse multi-directional, multi-actor and iterative innovation. Based on data from a real-time monitoring study, this article explores the development of 18 R&D centres’ external connections. University-based R&D centres establish more new connections than company-based centres and are more likely to be interacting with small or micro-firms. However, there is a general bias towards links with larger firms; micro, small and medium-sized enterprises also are less likely to be involved in collaborative R&D with research centres than other types of relationships. The results suggest the potential for R&D centres to act as a catalyst for open innovation but emphasise the need to ensure that the focus of the R&D being conducted is relevant to the needs of smaller firms.

Epitaxial strain stabilization of ferroelectric phase in PbZrO3 thin films

PbZrO3/SrRuO3/SrTiO3 (100) epitaxial heterostructures with different thickness of the PbZrO3 (PZO) layer (d(PZO) similar to 5-160 nm) were fabricated by pulsed laser deposition. The ultrathin PZO films (d(PZO) <= 10 nm) were found to possess a rhombohedral structure. On increasing the PZO film thickness, a bulk like orthorhombic phase started forming in the film with d(PZO) similar to 22 nm and became abundant in the thicker films. Nanobeam electron diffraction and room-temperature micro-Raman measurements revealed that the stabilization of the rhombohedral phase of PZO could be attributed to the epitaxial strain accommodated by the heterostructures. Room-temperature polarization vs electric field measurements performed on different samples showed characteristic double hysteresis loops of antiferroelectric materials accompanied by a small remnant polarization for the thick PZO films (dPZO >= 50 nm). The remnant polarization increased by reducing the PZO layer thickness, and a ferroelectric like hysteresis loop was observed for the sample with d(PZO) similar to 22 nm. Local ferroelectric properties measured by piezoresponse force microscopy also exhibited a similar thickness-dependent antiferroelectric-ferroelectric transition. Room-temperature electrical properties observed in the PZO thin films in correlation to their structural characteristics suggested that a ferroelectric rhombohedral phase could be stabilized in thin epitaxial PZO films experiencing large interfacial compressive stress.

Membrane Topology and Identification of Critical Amino Acid Residues in the Wzx O-Antigen Translocase from Escherichia coli O157:H4

Wzx belongs to a family of membrane proteins involved in the translocation of isoprenoid lipid-linked glycans, which is loosely related to members of the major facilitator superfamily. Despite Wzx homologs performing a conserved function, it has been difficult to pinpoint specific motifs of functional significance in their amino acid sequences. Here, we elucidate the topology of the Escherichia coli O157 Wzx (Wzx(EcO157)) by a combination of bioinformatics and substituted cysteine scanning mutagenesis, as well as targeted deletion-fusions to green fluorescent protein and alkaline phosphatase. We conclude that Wzx(EcO157) consists of 12 transmembrane (TM) helices and six periplasmic and five cytosolic loops, with N and C termini facing the cytoplasm. Four TM helices (II, IV, X, and XI) contain polar residues (aspartic acid or lysine), and they may form part of a relatively hydrophilic core. Thirty-five amino acid replacements to alanine or serine were targeted to five native cysteines and most of the aspartic acid, arginine, and lysine residues. From these, only replacements of aspartic acid-85, aspartic acid-326, arginine-298, and lysine-419 resulted in a protein unable to support O-antigen production. Aspartic acid-85 and lysine-419 are located in TM helices II and XI, while arginine-298 and aspartic acid-326 are located in periplasmic and cytosolic loops 4, respectively. Further analysis revealed that the charge at these positions is required for Wzx function since conservative substitutions maintaining the same charge polarity resulted in a functional protein, whereas those reversing or eliminating polarity abolished function. We propose that the functional requirement of charged residues at both sides of the membrane and in two TM helices could be important to allow the passage of the Und-PP-linked saccharide substrate across the membrane.

Photon collisions with atoms and ions within an intermediate-energy R-matrix framework

Recent experimental advances in light technology necessitate the availability of sophisticated theoretical models which can incorporate an accurate treatment of double-electron continua. We describe here a new intermediate-energy R-matrix approach to photoionisation and photo-double-ionisation and illustrate its feasibilty by application to photoionisation and photo-double-ionisation of He, and photodetachment and photo-double-detachment of H^-. Results are shown to be in excellent agreement with previous theoretical and experimental studies. This work is a key step in the development of a multipurpose R-matrix code for multiple-electron ejection. © 2012 American Physical Society

Identification of a UDP-Gal:GlcNAc-R galactosyltransferase activity in Escherichia coli VW187

A novel acceptor substrate for galactosyltransferase was synthesized containing GlcNAcalpha-pyrophosphate, covalently bound to a hydrophobic phenoxyundecyl moiety (GlcNAc alpha-O-PO(3)-PO(3)-(CH(2))(11)-O-Phenyl). The new substrate was used to develop an assay for a galactosyltransferase activity from Escherichia coli strain VW187 that is involved in lipopolysaccharide synthesis and has not been studied by others. We showed that Gal was transferred from UDP-Gal to the novel acceptor substrate. This was a significant improvement over our previous preliminary assays of the enzyme using endogenous substrate, and showed that these synthetic substrates are useful for assaying enzymes that utilize lipid-bound substrates in O-chain synthesis in Gram-negative bacteria.

The wbbD gene of E. coli strain VW187 (O7:K1) encodes a UDP-Gal:GlcNAc{alpha}-pyrophosphate-R {beta}1,3-galactosyltransferase involved in the biosynthesis of O7-specific lipopolysaccharide

In this work, we demonstrate that the wbbD gene of the O7 lipopolysaccharide (LPS) biosynthesis cluster in Escherichia coli strain VW187 (O7:K1) encodes a galactosyltransferase involved in the synthesis of the O7-polysaccharide repeating unit. The galactosyltransferase catalyzed the transfer of Gal from UDP-Gal to the GlcNAc residue of a GlcNAc-pyrophosphate-lipid acceptor. A mutant strain with a defective wbbD gene was unable to form O7 LPS and lacked this specific galactosyltransferase activity. The normal phenotype was restored by complementing the mutant with the cloned wbbD gene. To characterize the WbbD galactosyltransferase, we used a novel acceptor substrate containing GlcNAcalpha-pyrophosphate covalently bound to a hydrophobic phenoxyundecyl moiety (GlcNAc alpha-O-PO(3)-PO(3)-(CH(2))(11)-O-phenyl). The WbbD galactosyltransferase had optimal activity at pH 7 in the presence of 2.5 mM MnCl(2). Detergents in the assay did not increase glycosyl transfer. Digestion of enzyme product by highly purified bovine testicular beta-galactosidase demonstrated a beta-linkage. Cleavage of product by pyrophosphatase and phosphatase, followed by HPLC and NMR analyses, revealed a disaccharide with the structure Gal beta1-3GlcNAc. Our results conclusively demonstrate that WbbD is a UDP-Gal: GlcNAcalpha-pyrophosphate-R beta1,3-galactosyltransferase and suggest that the novel synthetic glycolipid acceptor may be generally applicable to characterize other bacterial glycosyltransferases.

B-spline methods in R-matrix theory for scattering in two-electron systems

The use of B-spline basis sets in R-matrix theory for scattering processes has been investigated. In the present approach a B-spline basis is used for the description of the inner region, which is matched to the physical outgoing wavefunctions by the R-matrix. Using B-splines, continuum basis functions can be determined easily, while pseudostates can be included naturally. The accuracy for low-energy scattering processes is demonstrated by calculating inelastic scattering cross sections for e colliding on H. Very good agreement with other calculations has been obtained. Further extensions of the codes to quasi two-electron systems and general atoms are discussed as well as the application to (multi) photoionization.