Phosphate Starvation Triggers Production and Secretion of an Extracellular Lipoprotein in Caulobacter crescentus

Life in oligotrophic environments necessitates quick adaptive responses to a sudden lack of nutrients. Secretion of specific degradative enzymes into the extracellular medium is a means to mobilize the required nutrient from nearby sources. The aquatic bacterium Caulobacter crescentus must often face changes in its environment such as phosphate limitation. Evidence reported in this paper indicates that under phosphate starvation, C. crescentus produces a membrane surface-anchored lipoprotein named ElpS subsequently released into the extracellular medium. A complete set of 12 genes encoding a type II secretion system (T2SS) is located adjacent to the elpS locus in the C. crescentus genome. Deletion of this T2SS impairs release of ElpS in the environment, which surprisingly remains present at the cell surface, indicating that the T2SS is not involved in the translocation of ElpS to the outer membrane but rather in its release. Accordingly, treatment with protease inhibitors prevents release of ElpS in the extracellular medium suggesting that ElpS secretion relies on a T2SS-secreted protease. Finally, secretion of ElpS is associated with an increase in alkaline phosphatase activity in culture supernatants, suggesting a role of the secreted protein in inorganic phosphate mobilization. In conlusion, we have shown that upon phosphate starvation, C. crescentus produces an outer membrane bound lipoprotein, ElpS, which is further cleaved and released in the extracellular medium in a T2SS-dependent manner. Our data suggest that ElpS is associated with an alkaline phosphatase activity, thereby allowing the bacterium to gather inorganic phosphates from a poor environment

Measurement of the W mass by direct reconstruction in e+e−e^+ e^- collisions at 172 GeV

The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 10.65~pb$^{-1}$ collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 \GEV. The invariant mass distribution of simulated events are fitted to the experimental distributions and the following W masses are obtained: $WW \to q\overline{q}q\overline{q } m_W = 81.30 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to l\nu q\overline{q}(l=e,\mu) m_W = 80.54 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to \tau\nu q\overline{q} m_W = 79.56 +- 1.08(stat.) +- 0.23(syst.) GeV/C62$. The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data. The combination of these measurements gives: $m_W = 80.80 +- 0.11(syst.) +- 0.03(LEP energy) GeV/^2$

Anodic Polarization in Molten Silicates

The anodic polarization in binary sodium silicates containing 22-40 mol% Na2O equilibrated with air was studied at 1000 degrees C by means of voltammetry and double-step chronoamperometry. The electrochemical oxidation of the oxide ions produced by condensation reactions of silicate species is a two-electron process kinetically controlled by mass transport of O2- to the anode. The oxygen atoms generated by the oxidation rapidly dimerize to produce dissolved oxygen which is further transformed into gaseous oxygen in the saturated bulk liquid. In basic liquids, the voltammetric peak corresponding to oxygen evolution is preceded by a prewave which has been explained by the formation of chemisorbed peroxide ions via an electrochemical reaction which involves dissolved and adsorbed oxide ions

Qualitative and Quantitative Electrochemical Studies of Multivalent Elements in Molten Oxide Glasses

The use of electrochemical techniques related to the investigation of multivalent species in molten oxide melts has been discussed. Because important oxoacidobasic perturbations can occur at the electrode surface during the electrochemical reactions of oxocomplexes, only techniques characterized by a negligible electrolysis, such as Normal Pulse Voltammetry, Differential Normal Pulse Voltammetry in the Alternating Pulse Mode and the Repetitive Multi-Pulse Chronoamperometry, are suitable to be applied to such very viscous melts. In this work, the analysis and the comparison of various electroanalytical techniques are grounded on experimental parameters especially defined in that purpose

Electrochemical behaviour of sulfate in sodium silicates at 1000 degrees C

The electrochemical behaviour of sulfate in Na2O . 2.5SiO(2) at 1000 degrees C is studied by means of cyclic voltammetry, square wave voltammetry and impedance spectroscopy. It appears that the thermal decomposition of sodium sulfate in Na2O . 2.5SiO(2) at 1000 degrees C is a complete and fast process providing a melt containing S(IV). The voltammograms show two reduction peaks attributed to the reduction of sulfite ions to elementary sulfur. The first peak corresponds to a reduction involving strong adsorption of sulfur on the electrode. The formation of a layer of adsorbed sulfur atoms during the prewave occurring anodic to the normal diffusion peak has a strong influence on the double layer capacitance measured by impedance spectroscopy. (C) 1996 Elsevier Science Ltd

Effect of basicity on redox equilibria in sodium silicate melts: An in situ electrochemical investigation

Redox ratios of chromium and antimony were directly measured at 1000 degrees C in sodium silicate melts by electrochemical methods. The redox ratios were found to increase while increasing the sodium oxide content, i.e. the liquid basicity. It was shown that the logarithm of the redox ratio is a linear function of the logarithm of the sodium oxide activity. Our results differ systematically from those obtained on quenched samples. The results are discussed in the light of a thermodynamic model considering activities of molecular species. We suggest that, when dissolved in silicate melts, multivalent ions form oxocomplexes which are not fully discrete species because non-bridging oxygens can intervene in their coordination sphere. We also concluded that there are rapid exchanges of oxygen atoms between the oxocomplexes and the solvent

Comparison between high temperature UV-visible spectroscopy and electrochemistry for the in situ study of redox equilibria in glass-forming melts

The redox ratio, R = C-Cr(VI)/C-Cr(III), in a glass-forming liquid with composition Na2O . 1.2SiO(2) . 1.2B(2)O(3) to which was added Na2CrO4 . 4H(2)O was directly determined at 1000 degrees C under various oxygen partial pressures using voltammetric techniques and high temperature spectrophotometry. The linearity of the log(R) vs log(P-O2) function was confirmed. The absorption spectra of the chromium species were recorded in the quenched glass at normal temperature and in the liquid at 1000 degrees C. The affects of temperature on the charge transfer bonds of Cr(VI) and on the d-d bands of Cr(III) are discussed. Whereas, the d-d bands related to Cr(III) in an octahedral coordination undergo a broadening and a large displacement towards the LR while increasing temperature, no variation of the charge transfer band of Cr(VI) is observed. (C) 1998 Elsevier Science B.V

In-situ Electrochemical Investigation of Copper in Binary Sodium-silicate Melts At 1000-degrees-c

The influence of the melt composition on the redox ratio of copper in binary sodium silicates at 1000 degrees C was determined by means of in situ electrochemical methods. The redox ratio was calculated from the currents measured by Repetitive Multi-Pulse Chronoamperometry. It appears that the redox ratio does not depend on the total copper concentration over the range 0.25 to 1 wt% Cu. However, the proportion of copper(II) was found to increase with increasing basicity, ie with increasing the sodium oxide content. We deduced from a model based on the formation of pure ionic oxocomplexes that the coordination number of the Cu(II) oxocomplex is greater than that of the Cu(I) oxocomplex. The difference between the coordination numbers, which is calculated from the experimental results is equal to 0.56. The fractional number is quite far from the integer that would indicate the occurrence of well defined oxocomplexes of copper

Evidence for Rh(II) in a LiCl-KCl eutectic. An optical absorption investigation

Rhodium exists in LiCl-KCl melts at 400-450 degrees C as the RhCl63- species. Spectroscopic data show that an increase of the temperature up to 600 degrees C leads to a reaction of this species with the melt and to the formation of the stable Rh(II) chlorocomplex. This reaction, which has not been reported previously, is reversible since on cooling to lower temperatures, 400-450 degrees C, reoxidation to the Rh(III) complex is observed. The Rh(ll) complex however persists even at these lower temperatures if the experimental cell is connected to a vacuum line to remove the chlorine formed in the reduction reaction