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Selected AbstractsIron uptake is essential for Escherichia coli survival in drinking waterLETTERS IN APPLIED MICROBIOLOGY, Issue 1 2006D. Grandjean Abstract Aims:, The aim of this study was to elucidate if the need for iron for Escherichia coli to remain cultivable in a poorly nutritive medium such as the drinking water uses the iron transport system via the siderophores. Methods and Results:, Environmental strains of E. coli (isolated from a drinking water network), referenced strains of E. coli and mutants deficient in TonB, an essential protein for iron(III) acquisition, were incubated for 3 weeks at 25°C, in sterile drinking water with and without lepidocrocite (, -FeOOH), an insoluble iron corrosion product. Only cells with a functional iron transport system were able to survive throughout the weeks. Conclusions:, The iron transport system via protein TonB plays an essential role on the survival of E. coli in a weakly nutritive medium like drinking water. Significance and Impacts of the Study:, Iron is a key parameter involved in coliform persistence in drinking water distribution systems. [source] Large-scale distribution and activity patterns of an extremely low-light-adapted population of green sulfur bacteria in the Black SeaENVIRONMENTAL MICROBIOLOGY, Issue 5 2010Evelyn Marschall Summary The Black Sea chemocline represents the largest extant habitat of anoxygenic phototrophic bacteria and harbours a monospecific population of Chlorobium phylotype BS-1. High-sensitivity measurements of underwater irradiance and sulfide revealed that the optical properties of the overlying water column were similar across the Black Sea basin, whereas the vertical profiles of sulfide varied strongly between sampling sites and caused a dome-shaped three-dimensional distribution of the green sulfur bacteria. In the centres of the western and eastern basins the population of BS-1 reached upward to depths of 80 and 95 m, respectively, but were detected only at 145 m depth close to the shelf. Using highly concentrated chemocline samples from the centres of the western and eastern basins, the cells were found to be capable of anoxygenic photosynthesis under in situ light conditions and exhibited a photosynthesis,irradiance curve similar to low-light-adapted laboratory cultures of Chlorobium BS-1. Application of a highly specific RT-qPCR method which targets the internal transcribed spacer (ITS) region of the rrn operon of BS-1 demonstrated that only cells at the central station are physiologically active in contrast to those at the Black Sea periphery. Based on the detection of ITS-DNA sequences in the flocculent surface layer of deep-sea sediments across the Black Sea, the population of BS-1 has occupied the major part of the basin for the last decade. The continued presence of intact but non-growing BS-1 cells at the periphery of the Black Sea indicates that the cells can survive long-distant transport and exhibit unusually low maintenance energy requirements. According to laboratory measurements, Chlorobium BS-1 has a maintenance energy requirement of ,1.6,4.9·10,15 kJ cell,1 day,1 which is the lowest value determined for any bacterial culture so far. Chlorobium BS-1 thus is particularly well adapted to survival under the extreme low-light conditions of the Black Sea, and can be used as a laboratory model to elucidate general cellular mechanisms of long-term starvation survival. Because of its adaptation to extreme low-light marine environments, Chlorobium BS-1 also represents a suitable indicator for palaeoceanography studies of deep photic zone anoxia in ancient oceans. [source] Embryonic erythropoiesis in human yolk sac: Two different compartments for two different processesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 12 2008Jaime Pereda Abstract The wall of 12 yolk sacs (YSs) from 17- to 50-day-old human embryos was examined by light, scanning, and transmission electron microscopy to identify the ontogeny of embryonic erythropoiesis. Initial formation of blood island with the generation of erythroid and endothelial cells was seen in the mesenchymal layer in embryos aged 17 days. A network of blood vessels containing abundant erythroblasts was identified in the YS walls of embryos aged ,24 days. At this age, erythroblasts were also identified within the embryo body. Primitive erythroblasts were the only cells present within the embryo and its YS until the end of week 5. These cells first appeared in the mesenchymal vascular plexus of the YS wall, and were then observed in the liver and other tissues of the embryo. At embryonic week 5, two compartments were identified in the YS wall; a mesodermal one in which blood vessels were formed, and an endodermal compartment in which erythrocytes were present within the endodermal vesicles. Erythrocytes were small non-nucleated cells similar to adult erythrocytes. Transmission electron microscopic observation focused on the endodermal vesicles confirmed the presence of definitive erythrocytes only at such extra vascular location. At this age, there were no definitive erythrocytes detected within the embryo. Erythrocytes started to be identified in embryonic blood vessels from week 7 onward. These findings provide information not previously described about YS erythropoiesis during early human development. Microsc. Res. Tech., 2008. © 2008 Wiley-Liss, Inc. [source] Actinobacillus actinomycetemcomitans induces apoptosis of T lymphocytes by the Fas and Fas ligand pathwayMOLECULAR ORAL MICROBIOLOGY, Issue 5 2002A. Nalbant Actinobacillus actinomycetemcomitans expresses a number of toxins capable of inducing apoptotic cell death of T lymphocytes. However, the exact mechanism(s) has not been elucidated. The present study investigated the involvement of the Fas (CD95)-mediated apoptotic pathway in A. actinomycetemcomitans -induced T-cell apoptosis. To that end, peripheral blood mononuclear cells (PBMC) were cultured with or without A. actinomycetemcomitans cell-free culture supernatant (CFCS) for 0,96 h. The cells were then labeled with specific monoclonal antibodies and flow cytometry was performed. Results demonstrated up-regulation of Fas and activation of caspase-3 in T cells in response to A. actinomycetemcomitans CFCS. Monocytes were the only cells analyzed to express Fas ligand (FasL) constitutively, and this was further up-regulated in response to A. actinomycetemcomitans CFCS, while T cells expressed FasL only after this stimulation. Depletion of monocytes prior to stimulation with A. actinomycetemcomitans CFCS led to a marked decline in apoptosis. Blocking of Fas,FasL interactions with anti-Fas monoclonal antibody or Fas:Fc fusion protein lead to a significant decline, but not abolition, of T-cell apoptosis. Nearly all T cells expressed Bcl-2 at the outset of culture, and Bcl-2 expression declined in T cells stimulated with A. actinomycetemcomitans CFCS. Collectively, these data provide evidence for the induction of T-cell apoptosis by A. actinomycetemcomitans via the Fas-mediated pathway, involving caspase-3 and Bcl- 2. Moreover, this apoptotic response was dependent on the presence of monocytes. [source] | |||||||||||||