Long-Term Anaerobic Survival of the Opportunistic Pathogen Pseudomonas aeruginosa via Pyruvate Fermentation

Der anaerobe Energiestoffwechsel ist eine der Grundlagen für die Biofilmbildung und die Infektion durch das opportunistisch pathogene Bakterium P. aeruginosa. Im Rahmen der vorliegenden Arbeit konnte erstmals gezeigt werden, dass die anaerobe Fermentation von Pyruvat zu Lactat, Acetat und Succinat die Basis für das Langzeitüberleben dieses Organismus bis zu 17 Tagen bietet. Dabei wird die beteiligte Lactat-Dehydrogenase vom ldhA-Gen kodiert, das unabhängig vom Sauerstoffpartialdruck exprimiert wird. Die für die Acetatbildung nötigen Enzyme Phosphotransacetylase und Acetatkinase werden durch das ackA-pta-Operon kodiert, welches über den Sauerstoffregulator Anr und das DNA-biegende Protein IHF induziert wird. Zugehörige Bindestellen für diese Regulatoren wurden stromaufwärts des ackA-pta-Operons identifiziert. Schließlich wurde das Anr-abhängige Proteom von P. aeruginosa mittels 2-D Gelelektrophorese bestimmt. Es enthielt Proteine der Denitrifikation, der Arginin-Fermentation sowie die zugehörigen Enzyme der Biosynthese benötigter Kofaktoren und Transporter. Die erzielten Ergebnisse geben erste detaillierte Einblicke in das Zusammenspiel Anr-abhängiger Prozesse während unterschiedlicher anaerober Adaptationsprozesse.Denitrification and arginine fermentation are central metabolic processes performed by the opportunistic pathogen Pseudomonas aeruginosa during biofilm formation and infections of lungs of patients with cystic fibrosis. Genome wide searches for additional components of the anaerobic metabolism identified potential genes for pyruvate metabolizing NADH-dependent lactate dehydrogenase (ldhA), phosphotransacetylase (pta) and acetate kinase (ackA). While pyruvate fermentation alone does not sustain significant anaerobic growth of P. aeruginosa, it provides the bacterium with the metabolic capacity for long-term survival of up to 17 days. Detected conversion of pyruvate to lactate and acetate is dependent on the presence of intact ldhA and ackA-pta loci, respectively. Reporter gene fusion analysis and enzyme activity measurements demonstrated the anr- and ihfA-dependent anaerobic induction of the ackA-pta promoter. Potential Anr and IHF binding sites were localized. No obvious ldhA regulation by oxygen tension was observed. In the second part of this work the Anr-dependent proteome of P. aeruginosa was investigated by 2-D gel electrophoresis. Proteins involved in denitrification, arginine fermentation and enzymes for the corresponding cofactors and transporters were identified. Furthermore serveral previously unknown Anr-dependnet putative promoters were identified

Electrical resistance of individual defects at a topological insulator surface

Three-dimensional topological insulators host surface states with linear dispersion, which manifest as a Dirac cone. Nanoscale transport measurements provide direct access to the transport properties of the Dirac cone in real space and allow the detailed investigation of charge carrier scattering. Here, we use scanning tunnelling potentiometry to analyse the resistance of different kinds of defects at the surface of a (Bi0.53Sb0.47)2Te3 topological insulator thin film. The largest localized voltage drop we find to be located at domain boundaries in the topological insulator film, with a resistivity about four times higher than that of a step edge. Furthermore, we resolve resistivity dipoles located around nanoscale voids in the sample surface. The influence of such defects on the resistance of the topological surface state is analysed by means of a resistor network model. The effect resulting from the voids is found to be small compared to the other defects

Prymnesins: Toxic Metabolites of the Golden Alga, Prymnesium parvum Carter (Haptophyta)

Increasingly over the past century, seasonal fish kills associated with toxic blooms of Prymnesium parvum have devastated aquaculture and native fish, shellfish, and mollusk populations worldwide. Protracted blooms of P. parvum can result in major disturbances to the local ecology and extensive monetary losses. Toxicity of this alga is attributed to a collection of compounds known as prymnesins, which exhibit potent cytotoxic, hemolytic, neurotoxic and ichthyotoxic effects. These secondary metabolites are especially damaging to gill-breathing organisms and they are believed to interact directly with plasma membranes, compromising integrity by permitting ion leakage. Several factors appear to function in the activation and potency of prymnesins including salinity, pH, ion availability, and growth phase. Prymnesins may function as defense compounds to prevent herbivory and some investigations suggest that they have allelopathic roles. Since the last extensive review was published, two prymnesins have been chemically characterized and ongoing investigations are aimed at the purification and analysis of numerous other toxic metabolites from this alga. More information is needed to unravel the mechanisms of prymnesin synthesis and the significance of these metabolites. Such work should greatly improve our limited understanding of the physiology and biochemistry of P. parvum and how to mitigate its blooms

Multi-messenger observations of a binary neutron star merger

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]