Papers by Alexander Zehnder
Le château d'eau de l'Europe et la protection des eaux
Eawag News [éd. fr.], 2001
Wasserressourcen und Bevölkerungsentwicklung
Nova acta Leopoldina, 2002
The anaerobic degradation of polycyclic aromatic hydrocarbons under different redoxconditions
An analysis of water scarcity-induced cereal grain import
Microbial reductive dechlorination of hexachloro-1,3-butadiene
Reductive dechlorination of hexochlorocyclohexane isomers
Phosphate transport in Acinetobacter johnsonii 210A
The anaerobic energy metabolism in activated sludge showing biological phosphorus removal
Characterization of a reversible secondary phosphate transport system in Acinetobacter johnsonii 210A
Pi efflux in Acinetobacter johnsonii 210A: analysis of mechanism and energy coupling
Mechanism and energetics of the secondary phosphate transport system of Acinetobacter johnsonii 210A
Journal of Biological Chemistry, 1993
The mechanism and energetics of the secondary Pi transport system of A. johnsonii were studied in... more The mechanism and energetics of the secondary Pi transport system of A. johnsonii were studied in membrane vesicles and proteoliposomes in which the transport protein was functionally reconstituted. Pi uptake is strictly dependent on the presence of divalent cations, like Mg2+, Ca2+, Mn2+, or Co2+. These cations form a MeHPO4 complex with up to 87% of the Pi present in the incubation mixture, suggesting that divalent cations and Pi are co-transported via a metal-phosphate chelate. Metal-phosphate uptake is driven by the proton motive force (interior negative and alkaline). The metal-phosphate/proton stoichiometry was close to unity. The transport system mediates efflux and homologous exchange of metal-phosphate, but not heterologous exchange of metal-phosphate and glycerol-3-P or glucose-6-P. Exchange and counterflow were essentially pH-independent while efflux and uptake increased with increasing pH. Efflux was inhibited by the proton motive force, whereas exchange was inhibited by the membrane potential only. These observations are consistent with an ordered mechanism for binding and dissociation of metal-phosphate and proton to and from the carrier protein and point to the recycling of a positively charged, protonated carrier protein during exchange.
Substrate specificity of the two phosphate transport systems of Acinetobacter johnsonii 210A in relation to phosphate speciation in its aquatic environment
Journal of Biological Chemistry, 1994
In natural waters and domestic waste waters in which divalent metal ions are present in excess of... more In natural waters and domestic waste waters in which divalent metal ions are present in excess of Pi, H2PO4-, HPO4(2-), and MeHPO4 prevail at pH values physiological for Acinetobacter johnsonii 210A (pH 5.5-8.0). In view of the ability of this organism to extensively accumulate Pi and divalent cations in cytoplasmic polyphosphate granules, the substrate specificity of its two Pi transport systems was studied. The constitutive, proton motive force-driven Pi carrier, previously shown to be dependent on divalent cations, plays a major role in the divalent cation and Pi flux by translocating MeHPO4 rather than Pi. This notion is confirmed by the observation that divalent cations are cotransported with Pi in a 1:1 stoichiometry in proteoliposomes containing reconstituted Pi carrier protein. In contrast, the Pi repressible, periplasmic binding protein-dependent Pi transport system mediates the uptake of H2PO4- and HPO4(2-). Pi uptake, but not MeHPO4 uptake, was stimulated in cells under Pi limitation, and the periplasmic Pi-binding protein has affinity for H2PO4- and HPO4(2-), but not for MeHPO4. When operating in concert, both systems enable A. johnsonii 210A to efficiently acquire Pi from its habitat through uptake of the predominant Pi species.
Environmental Science & Policy, 2018
Long-term reviews are necessary to appreciate the full outcomes and impacts of the scientific, so... more Long-term reviews are necessary to appreciate the full outcomes and impacts of the scientific, societal and policy perspectives of transdisciplinary projects. Here, thirteen years after its completion, we assess the significance of a five-year (1999-2004) Swiss research project. The Fischnetz project aimed to identify the causes of fish catch decline and propose remedial measures. Engineers and scientists from different disciplines collaborated with practitioners and policy makers to approach this real-world problem and develop and implement policy interventions. Fischnetz proved to be an exemplarily successful case of how transgressive and socially robust research can be conducted and result in high-quality scientific outputs and policy impacts. As a result of Fischnetz, The Swiss Federal Water Protection Act was fully revised, two by-laws were changed, and several parliamentary interventions were launched. Fischnetz produced 68 scientific ISI-papers with higher than average citations. In this report, the project setup and its overall outcomes were analysed via a Mode-2 knowledge production approach.
Biodegradation of dibenzofurans in soil: degradation of dibenzofuran and 3-chlorodibenzofuran in a soil-model system
Reductive dechlorination of hexachloro-1,3,butadiene
Proceedings of the GASMAT Workshop on Granular anaerobic sludge; microbiology and technology
A model system for studying uptake and conversion of adsorbed organic (xenobiotics) compounds: PFA-teflon, Arthrobacter 177 and n-alcohols
The role of microbiological activity in well clogging related to aquifer thermal energy storage
Characterization of two alternative promoters for integrase expression in the clc genomic island of Pseudomonas sp. strain B13
Molecular Microbiology, 2003
The clc genomic island is a 105 kb integrative and conjugative element (ICE) in Pseudomonas sp. s... more The clc genomic island is a 105 kb integrative and conjugative element (ICE) in Pseudomonas sp. strain B13, which encodes metabolism of 3-chlorocatechol. The clc island is integrated in a tRNAGly gene, but can excise and form a circular intermediate in which both ends are connected. The integrase gene (intB13) of the clc genomic island is located at the right end, 202 bp from the junction site facing inwards. Fragments upstream of intB13 in the circular form and in the integrated form were fused to a promoterless gfp gene for Green Fluorescent Protein and introduced in monocopy onto the chromosome of strain B13. Quantitative GFP fluorescence measurements in individual cells of the different B13-derivatives revealed that the circular form fragment contained a strong constitutive promoter (Pcirc) driving intB13 expression in all cells. By using primer extension Pcirc could be mapped near the left end of the clc element and Pcirc can therefore only control intB13 expression when left and right ends are connected as in the circular form. Expression from intB13 upstream fragments from the integrated clc element was weaker than that from Pcirc and only occurred in maximally 15% of individual cells in a culture. A promoter (Pint) could be roughly mapped in this region by using reverse-transcription PCR and by successively shortening the fragment from the 5' end. Transposon mutants in cloned left end sequences of the clc element were selected which had lost the activation potential on the Pint promoter and those which resulted in overexpression of GFP from Pint. The DNA sequence of the region of the transposon insertions pointed to a relatively well conserved area among various other genomic islands. The activator mutants mapped in an open reading frame (ORF) encoding a 175 amino acid protein without any significant similarity to functionally characterized proteins in the databases.
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Papers by Alexander Zehnder