Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis

<p>Abstract</p> <p>Background</p> <p>Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.</p> <p>Results</p> <p><it>Moraxella catarrhalis </it>strain E22 containing plasmid pLQ510 was shown to inhibit the growth of <it>M. catarrhalis </it>strain O35E. Two genes (<it>mcbA </it>and <it>mcbB</it>) in pLQ510 encoded proteins predicted to be involved in the secretion of a bacteriocin. Immediately downstream from these two genes, a very short ORF (<it>mcbC</it>) encoded a protein which had some homology to double-glycine bacteriocins produced by other bacteria. A second very short ORF (<it>mcbI</it>) immediately downstream from <it>mcbC </it>encoded a protein which had no significant similarity to other proteins in the databases. Cloning and expression of the <it>mcbI </it>gene in <it>M. catarrhalis </it>O35E indicated that this gene encoded the cognate immunity factor. Reverse transcriptase-PCR was used to show that the <it>mcbA</it>, <it>mcbB</it>, <it>mcbC</it>, and <it>mcbI </it>ORFs were transcriptionally linked. This four-gene cluster was subsequently shown to be present in the chromosome of several <it>M. catarrhalis </it>strains including O12E. Inactivation of the <it>mcbA</it>, <it>mcbB</it>, or <it>mcbC </it>ORFs in <it>M. catarrhalis </it>O12E eliminated the ability of this strain to inhibit the growth of <it>M. catarrhalis </it>O35E. In co-culture experiments involving a <it>M. catarrhalis </it>strain containing the <it>mcbABCI </it>locus and one which lacked this locus, the former strain became the predominant member of the culture after overnight growth in broth.</p> <p>Conclusion</p> <p>This is the first description of a bacteriocin and its cognate immunity factor produced by <it>M. catarrhalis</it>. The killing activity of the McbC protein raises the possibility that it might serve to lyse other <it>M. catarrhalis </it>strains that lack the <it>mcbABCI </it>locus, thereby making their DNA available for lateral gene transfer.</p

How ready is China for a China-style world order? China's state media discourse under construction

What exactly is the China-style world order that Chinese officials and intellectual elites have recently been talking about, and how ready is China for it? An examination and analysis of discourses on ‘Africa Live’ on CCTV Africa, the first overseas news center of China Central Television (CCTV), yields some highly noticeable features and significant themes, confirming that although China has shifted from a low-profile approach to a more assertive one, in an attempt to change the global order, its verbal challenge and sometimes harsh criticism of the American-led international system is accompanied by an obvious absence of a clear vision of what the new world order should be like. This lack of a clear vision may be due to the fact that the Chinese discourse on world order is still a work in progress, constrained by internal practices, and Africa is its testing ground for the construction of a discourse that China envisages as an alternative

Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm

Abstract The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17-19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 - 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1-0.5fce (theelectron equatorial gyrofrequency), with a peak spectral density ∼10-4 nT 2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102-103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 h, fitting well with the observation. Key Points Initial RBSP correlated data of chorus waves and relativistic electron fluxes A realistic simulation to examine effect of chorus on relativistic electron flux Chorus yields huge increases inelectron flux rapidly, consistent with data

Nonstorm time dynamics of electron radiation belts observed by the Van Allen Probes

Abstract Storm time electron radiation belt dynamics have been widely investigated for many years. Here we present a rarely reported nonstorm time event of electron radiation belt evolution observed by the Van Allen Probes during 21-24 February 2013. Within 2 days, a new belt centering around L=5.8 formed and gradually merged with the original outer belt, with the enhancement of relativistic electron fluxes by a factor of up to 50. Strong chorus waves (with power spectral density up to 10-4nT2/Hz) occurred in the region L\u3e5. Taking into account the local acceleration driven by these chorus waves, the two-dimensional STEERB can approximately reproduce the observed energy spectrums at the center of the new belt. These results clearly illustrate the complexity of electron radiation belt behaviors and the importance of chorus-driven local acceleration even during the nonstorm times

Forward K+ production in subthreshold pA collisions at 1.0 GeV

K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.Comment: 4 pages, 3 figure

Global Conformational Dynamics of a Y-Family DNA Polymerase during Catalysis

High-resolution analysis of protein, and DNA conformational changes during DNA polymerization, established relationships between the enzymatic function and conformational dynamics of individual domains for a DNA polymerase

Neurochemical Changes in the Mouse Hippocampus Underlying the Antidepressant Effect of Genetic Deletion of P2X7 Receptors.

Recent investigations have revealed that the genetic deletion of P2X7 receptors (P2rx7) results in an antidepressant phenotype in mice. However, the link between the deficiency of P2rx7 and changes in behavior has not yet been explored. In the present study, we studied the effect of genetic deletion of P2rx7 on neurochemical changes in the hippocampus that might underlie the antidepressant phenotype. P2X7 receptor deficient mice (P2rx7-/-) displayed decreased immobility in the tail suspension test (TST) and an attenuated anhedonia response in the sucrose preference test (SPT) following bacterial endotoxin (LPS) challenge. The attenuated anhedonia was reproduced through systemic treatments with P2rx7 antagonists. The activation of P2rx7 resulted in the concentration-dependent release of [3H]glutamate in P2rx7+/+ but not P2rx7-/- mice, and the NR2B subunit mRNA and protein was upregulated in the hippocampus of P2rx7-/- mice. The brain-derived neurotrophic factor (BDNF) expression was higher in saline but not LPS-treated P2rx7-/- mice; the P2rx7 antagonist Brilliant blue G elevated and the P2rx7 agonist benzoylbenzoyl ATP (BzATP) reduced BDNF level. This effect was dependent on the activation of NMDA and non-NMDA receptors but not on Group I metabotropic glutamate receptors (mGluR1,5). An increased 5-bromo-2-deoxyuridine (BrdU) incorporation was also observed in the dentate gyrus derived from P2rx7-/- mice. Basal level of 5-HT was increased, whereas the 5HIAA/5-HT ratio was lower in the hippocampus of P2rx7-/- mice, which accompanied the increased uptake of [3H]5-HT and an elevated number of [3H]citalopram binding sites. The LPS-induced elevation of 5-HT level was absent in P2rx7-/- mice. In conclusion there are several potential mechanisms for the antidepressant phenotype of P2rx7-/- mice, such as the absence of P2rx7-mediated glutamate release, elevated basal BDNF production, enhanced neurogenesis and increased 5-HT bioavailability in the hippocampus

Unwinding of primer-templates by archaeal family-B DNA polymerases in response to template-strand uracil

Archaeal family-B DNA polymerases bind tightly to deaminated bases and stall replication on encountering uracil in template strands, four bases ahead of the primer-template junction. Should the polymerase progress further towards the uracil, for example, to position uracil only two bases in front of the junction, 3′–5′ proof-reading exonuclease activity becomes stimulated, trimming the primer and re-setting uracil to the +4 position. Uracil sensing prevents copying of the deaminated base and permanent mutation in 50% of the progeny. This publication uses both steady-state and time-resolved 2-aminopurine fluorescence to show pronounced unwinding of primer-templates with Pyrococcus furiosus (Pfu) polymerase–DNA complexes containing uracil at +2; much less strand separation is seen with uracil at +4. DNA unwinding has long been recognized as necessary for proof-reading exonuclease activity. The roles of M247 and Y261, amino acids suggested by structural studies to play a role in primer-template unwinding, have been probed. M247 appears to be unimportant, but 2-aminopurine fluorescence measurements show that Y261 plays a role in primer-template strand separation. Y261 is also required for full exonuclease activity and contributes to the fidelity of the polymerase

Evidence for a Two-Metal-Ion Mechanism in the Cytidyltransferase KdsB, an Enzyme Involved in Lipopolysaccharide Biosynthesis

Lipopolysaccharide (LPS) is located on the surface of Gram-negative bacteria and is responsible for maintaining outer membrane stability, which is a prerequisite for cell survival. Furthermore, it represents an important barrier against hostile environmental factors such as antimicrobial peptides and the complement cascade during Gram-negative infections. The sugar 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) is an integral part of LPS and plays a key role in LPS functionality. Prior to its incorporation into the LPS molecule, Kdo has to be activated by the CMP-Kdo synthetase (CKS). Based on the presence of a single Mg2+ ion in the active site, detailed models of the reaction mechanism of CKS have been developed previously. Recently, a two-metal-ion hypothesis suggested the involvement of two Mg2+ ions in Kdo activation. To further investigate the mechanistic aspects of Kdo activation, we kinetically characterized the CKS from the hyperthermophilic organism Aquifex aeolicus. In addition, we determined the crystal structure of this enzyme at a resolution of 2.10 Å and provide evidence that two Mg2+ ions are part of the active site of the enzyme

S. aureus MscL Is a Pentamer In Vivo but of Variable Stoichiometries In Vitro: Implications for Detergent-Solubilized Membrane Proteins

Detergent-induced rearrangements of membrane-protein subunits explain why two MscL channel stoichiometries have been resolved by X-ray crystallography - but S. aureus MscL is truly a pentamer in vivo