Cytoplasmic and periplasmic signatures of exponentially growing cells of the psychrophilic bacterium <i>Pseudoalteromonas haloplanktis</i> TAC125

The psychrophilic model bacterium Pseudoalteromonas haloplanktis is characterized by remarkably fast growth rates under low-temperature conditions in a range from 5°C to 20°C. In this study the proteome of cellular compartments, the cytoplasm and periplasm, of P. haloplanktis strain TAC125 was analyzed under exponential growth conditions at a permissive temperature of 16°C. By means of two-dimensional protein gel electrophoresis and mass spectrometry, a first inventory of the most abundant cytoplasmic and periplasmic proteins expressed in a peptone-supplemented minimal medium was established. By this approach major enzymes of the amino acid catabolism of this marine bacterium could be functionally deduced. The cytoplasmic proteome showed a predominance of amino acid degradation pathways and tricarboxylic acid (TCA) cycle enzymes but also the protein synthesis machinery. Furthermore, high levels of cold acclimation and oxidative stress proteins could be detected at this moderate growth temperature. The periplasmic proteome was characterized by a significant abundance of transporters, especially of highly expressed putative TonB-dependent receptors. This high capacity for protein synthesis, efficient amino acid utilization, and substrate transport may contribute to the fast growth rates of the copiotrophic bacterium P. haloplanktis in its natural environments

Metatranscriptomics reveal differences in in situ energy and nitrogen metabolism among hydrothermal vent snail symbionts

Despite the ubiquity of chemoautotrophic symbioses at hydrothermal vents, our understanding of the influence of environmental chemistry on symbiont metabolism is limited. Transcriptomic analyses are useful for linking physiological poise to environmental conditions, but recovering samples from the deep sea is challenging, as the long recovery times can change expression profiles before preservation. Here, we present a novel, in situ RNA sampling and preservation device, which we used to compare the symbiont metatranscriptomes associated with Alviniconcha, a genus of vent snail, in which specific host–symbiont combinations are predictably distributed across a regional geochemical gradient. Metatranscriptomes of these symbionts reveal key differences in energy and nitrogen metabolism relating to both environmental chemistry (that is, the relative expression of genes) and symbiont phylogeny (that is, the specific pathways employed). Unexpectedly, dramatic differences in expression of transposases and flagellar genes suggest that different symbiont types may also have distinct life histories. These data further our understanding of these symbionts' metabolic capabilities and their expression in situ, and suggest an important role for symbionts in mediating their hosts' interaction with regional-scale differences in geochemistry

Status quo in physiological proteomics of the uncultured Riftia pachyptila endosymbiont

Riftia pachyptila, the giant deep-sea tube worm, inhabits hydrothermal vents in the Eastern Pacific ocean. The worms are nourished by a dense population of chemoautotrophic bacterial endosymbionts. Using the energy derived from sulfide oxidation, the symbionts fix CO(2) and produce organic carbon, which provides the nutrition of the host. Although the endosymbionts have never been cultured, cultivation-independent techniques based on density gradient centrifugation and the sequencing of their (meta-) genome enabled a detailed physiological examination on the proteomic level. In this study, the Riftia symbionts' soluble proteome map was extended to a total of 493 identified proteins, which allowed for an explicit description of vital metabolic processes such as the energy-generating sulfide oxidation pathway or the Calvin cycle, which seems to involve a reversible pyrophosphate-dependent phosphofructokinase. Furthermore, the proteomic view supports the hypothesis that the symbiont uses nitrate as an alternative electron acceptor. Finally, the membrane-associated proteome of the Riftia symbiont was selectively enriched and analyzed. As a result, 275 additional proteins were identified, most of which have putative functions in electron transfer, transport processes, secretion, signal transduction and other cell surface-related functions. Integrating this information into complex pathway models a comprehensive survey of the symbiotic physiology was established

Status of WENDELSTEIN 7-X construction

WENDELSTEIN 7-X (W7-X) shall confirm the favourable plasma properties and the high density and beta limits of the helical advanced stellarator and demonstrate steady-state operation. The magnetic configuration of W7-X is characterized by a set of 50 non-planar and 20 planar superconducting coils. The magnet system will be manufactured and assembled to a precision of a few millimetres and maintain its symmetry during cool-down to cryogenic temperatures. Power supplies allows one to adjust the magnetic field with a precision of a few milli Tesla and safely dump the magnet energy in case of a quench. The plasma vessel gives maximum space for the plasma and is kept symmetrically with respect to the plasma by dedicated means. Steady-state heating is achieved by 10 MW ECRH. Energy and particles are controlled by a continuously working divertor. All plasma-facing surfaces are covered by CFC, graphite or B4C, respectively. The paper reviews the status of the construction and describes details of the design