X-Ray Spectroscopy of Stars

(abridged) Non-degenerate stars of essentially all spectral classes are soft X-ray sources. Low-mass stars on the cooler part of the main sequence and their pre-main sequence predecessors define the dominant stellar population in the galaxy by number. Their X-ray spectra are reminiscent, in the broadest sense, of X-ray spectra from the solar corona. X-ray emission from cool stars is indeed ascribed to magnetically trapped hot gas analogous to the solar coronal plasma. Coronal structure, its thermal stratification and geometric extent can be interpreted based on various spectral diagnostics. New features have been identified in pre-main sequence stars; some of these may be related to accretion shocks on the stellar surface, fluorescence on circumstellar disks due to X-ray irradiation, or shock heating in stellar outflows. Massive, hot stars clearly dominate the interaction with the galactic interstellar medium: they are the main sources of ionizing radiation, mechanical energy and chemical enrichment in galaxies. High-energy emission permits to probe some of the most important processes at work in these stars, and put constraints on their most peculiar feature: the stellar wind. Here, we review recent advances in our understanding of cool and hot stars through the study of X-ray spectra, in particular high-resolution spectra now available from XMM-Newton and Chandra. We address issues related to coronal structure, flares, the composition of coronal plasma, X-ray production in accretion streams and outflows, X-rays from single OB-type stars, massive binaries, magnetic hot objects and evolved WR stars.Comment: accepted for Astron. Astrophys. Rev., 98 journal pages, 30 figures (partly multiple); some corrections made after proof stag

Long-Distance Delivery of Bacterial Virulence Factors by Pseudomonas aeruginosa Outer Membrane Vesicles

Bacteria use a variety of secreted virulence factors to manipulate host cells, thereby causing significant morbidity and mortality. We report a mechanism for the long-distance delivery of multiple bacterial virulence factors, simultaneously and directly into the host cell cytoplasm, thus obviating the need for direct interaction of the pathogen with the host cell to cause cytotoxicity. We show that outer membrane–derived vesicles (OMV) secreted by the opportunistic human pathogen Pseudomonas aeruginosa deliver multiple virulence factors, including β-lactamase, alkaline phosphatase, hemolytic phospholipase C, and Cif, directly into the host cytoplasm via fusion of OMV with lipid rafts in the host plasma membrane. These virulence factors enter the cytoplasm of the host cell via N-WASP–mediated actin trafficking, where they rapidly distribute to specific subcellular locations to affect host cell biology. We propose that secreted virulence factors are not released individually as naked proteins into the surrounding milieu where they may randomly contact the surface of the host cell, but instead bacterial derived OMV deliver multiple virulence factors simultaneously and directly into the host cell cytoplasm in a coordinated manner

The sense of smell, its signalling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells

Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existance of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use

Vaccines from the Spanish Influenza as a firm foundation for new developments

In 1914, the concept of a prophylactic vaccine, administered to a person before the disease had been contracted, was still controversial. Nevertheless, Almroth Wright tested new pneumococcus vaccines in South Africa, where the incidence of bacterial pneumonia was high amongst workers in the gold mines. He established the use of clinical trials, using around ten thousand workers, both in vaccinated and unvaccinated groups. The two groups were not matched to modern standards. Also, of course, those workers in the control unvaccinated group could not be protected: but some considered a prophylactic vaccine would exacerbate the disease. The vaccines were manufactured to contain a range of pneumococci from different clinical samples, in a serious attempt to match the microbes in the vaccine to the field bacteria. Deaths were averted by the vaccine; and side effects were noted to be minimal. Reexamination of pathology samples from the Spanish Influenza Pandemic showed quite clearly the contribution of pneumococci and streptococci to the mortality of over fifty million people in 1918–1919. The microbe causing this Pandemic was isolated in 1933, and was shown to be a true virus; this finding initiated a huge expanse and interest in influenza virus vaccines, both killed and live. A chance discovery allowed the purification of Influenza M and NP proteins then permitted the production of experimental vaccines. These vaccines were formulated to induce and B and/or T cell responses to the internal proteins. Several of these Universal Influenza Vaccines have been tested in quarantine, and have now reached Phase III trials in the community