Extragalactic jets on subpc and large scales

Jets can be probed in their innermost regions (d~0.1 pc) through the study of the relativistically-boosted emission of blazars. On the other extreme of spatial scales, the study of structure and dynamics of extragalactic relativistic jets received renewed impulse after the discovery, made by Chandra, of bright X-ray emission from regions at distances larger than hundreds of kpc from the central engine. At both scales it is thus possible to infer some of the basic parameters of the flow (speed, density, magnetic field intensity, power). After a brief review of the available observational evidence, I discuss how the comparison between the physical quantities independently derived at the two scales can be used to shed light on the global dynamics of the jet, from the innermost regions to the hundreds of kpc scale.Comment: Proceedings of the 5th Stromlo Symposium: Disks, Winds, and Jets - from Planets to Quasars. Accepted, to be published in Astrophysics & Space Scienc

Grain Surface Models and Data for Astrochemistry

AbstractThe cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions

Molecular genetics of Thiobacillus ferrooxidans and other mesophilic, acidophilic, chemolithotrophic, iron- or sulfur-oxidizing bacteria

The bacteria primarily responsible for decomposing metal sulfide ores and concentrates at temperatures of 40 °C or below have been identified as Thiobacillus ferrooxidans, Leptospirillum ferrooxidans (or related Leptospirillum spp.) T. thiooxidans and recently, T. caldus. These obligately acidophilic, autotrophic, usually aerobic, iron- or sulfur-oxidizing chemolithotrophic bacteria occupy an ecological niche that is largely inorganic and very different from that populated by the more commonly studied non-acidophilic heterotrophic bacteria. It has been of particular interest to discover how these `biomining' bacteria are phylogenetically related to the rest of the microbial world. Based on 16S rRNA sequence data, the thiobacilli have been placed in the Proteobacteria division close to the junction between the β and γ sub-divisions. In contrast, the leptospirilli have been positioned within a relatively recently recognized division called the Nitrospira group. T. ferrooxidans is the only biomining bacterium whose molecular biology has been studied in some detail. Of the approximately 50 genes cloned or sequenced and published, by far the majority that can be tested are expressed and produce proteins which are functional in Escherichia coli (a member of the γ sub-division of Proteobacteria). These observations together with phylogenetic comparisons of most T. ferrooxidans protein sequences have confirmed the unexpectedly close relationship between T. ferrooxidans and E. coli. A special challenge has been the isolation of the various components of the iron-oxidation system and as a result of a global effort, this is almost complete. Several plasmids, transposons and insertion sequences have been isolated from T. ferrooxidans. These genetic elements are interesting because they may contain non-essential genes which are thought to improve the fitness of the bacterium and are frequently mobile. They have provided some fascinating insights into genetic exchanges that have occurred between T. ferrooxidans and other bacteria. There are clear indications that some of the other `biomining' bacteria are even more important than T. ferrooxidans in many commercial biomining processes. The molecular biology of these bacteria is almost unstudied.Articl

Proteic toxin-antitoxin, bacterial plasmid addiction systems and their evolution with special reference to the pas system of pTF-FC2

Genes encoding toxin-antitoxin proteins are frequently found on plasmids where they serve to stabilize the plasmid within a bacterial population. The toxin-antitoxin proteins do not increase the likelihood of a progeny cell receiving a plasmid but rather function as post-segregational killing mechanisms which decrease the proportion of cells that survive after losing the plasmid. These toxin-antitoxin couples therefore act as plasmid addiction systems. Several new proteic toxin-antitoxin systems have been identified and these systems appear to be ubiquitous on the chromosomes of bacteria and archaea. When placed on plasmids, these chromosomal systems also have the ability to stabilize plasmids and in at least one case, chromosomal- and plasmid-based toxin-antitoxin systems have been shown to interact. Recent findings regarding toxin-antitoxin systems and questions that have arisen as a result of these findings are reviewed. Copyright (C) 1999 Federation of European Microbiological Societies.Revie

Autoregulation of the pTF-FC2 proteic poison-antidote plasmid addiction system (pas) is essential for plasmid stabilization

The pasABC genes of the proteic plasmid addiction system of broad-host- range plasmid pTF-FC2 were autoregulated. The PasA antidote was able to repress the operon 25-fold on its own, and repression was increased to 100- fold when the PasB toxin was also present. Autoregulation appears to be an essential requirement for pas-mediated plasmid stabilization because when the pas genes were placed behind the isopropyl-β-D-thiogalactopyranoside (IPTG)- regulated tac promoter, they were unable to stabilize a heterologous test plasmid.Articl

Production of rhodanese by bacteria present in bio-oxidation plants used to recover gold from arsenopyrite concentrates

Considerably larger quantities of cyanide are required to solubilize gold following the bio-oxidation of gold-bearing ores compared with oxidation by physical-chemical processes. A possible cause of this excessive cyanide consumption is the presence of the enzyme rhodanese. Rhodanese activities were determined for the bacteria most commonly encountered in bio-oxidation tanks. Activities of between 6.4 and 8.2 μmol SCN- min-1 mg protein -1 were obtained for crude enzyme extracts of Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Thiobacillus caldus, but no rhodanese activity was detected in Leptospirillum ferrooxidans. Rhodanese activities 2-2.5-fold higher were found in the total mixed cell mass from a bio-oxidation plant. T. ferrooxidans synthesized rhodanese irrespective of whether it was grown on iron or sulphur. With a PCR-based detection technique, only L. ferrooxidans and T. caldus cells were detected in the bio-oxidation tanks. As no rhodanese activity was associated with L. ferrooxidans, it was concluded that T. caldus was responsible for all of the rhodanese activity. Production of rhodanese by T. caldus in batch culture was growth phase-dependent and highest during early stationary phase. Although the sulphur-oxidizing bacteria were clearly able to convert cyanide to thiocyanate, it is unlikely that this rhodanese activity is responsible for the excessive cyanide wastage at the high pH values associated with the gold solubilization process.Articl

Efficiency of the pTF-FC2 pas Poison-antidote stability system in Escherichia coli is affected by the host strain, and antidote degradation requires the Lon protease

The stabilization of a test plasmid by the proteic, poison-antidote plasmid addiction system (pas) of plasmid pTF-FC2 was host strain dependent, with a 100-fold increase in stability in Escherichia coli CSH50, a 2.5-fold increase in E. coli JM105, and no detectable stabilization in E. coli strains JM107 and JM109. The lethality of the PasB toxin was far higher in the E. coli strains in which the pas was most effective. Models for the way in which poison-antidote systems stabilize plasmids require that the antidote have a much higher rate of turnover than that of the toxin. A decrease in host cell death following plasmid loss from an E. coli lon mutant and a decrease in plasmid stability suggested that the Lon protease plays a role in the rate of turnover of PasA antidote.Articl