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  • 1
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The filamentous bacterium Streptomyces coelicolor undergoes a complex process of morphological differentiation involving the formation of a dense lawn of aerial hyphae that grow away from the colony surface into the air to form an aerial mycelium. Bald mutants of S. coelicolor, which are blocked in aerial mycelium formation, regain the capacity to erect aerial structures when exposed to a small hydrophobic protein called SapB, whose synthesis is temporally and spatially correlated with morphological differentiation. We now report that SapB is a surfactant that is capable of reducing the surface tension of water from 72 mJ m−2 to 30 mJ m−2 at a concentration of 50 μg ml−1. We also report that SapB, like the surface-active peptide streptofactin produced by the species S. tendae, was capable of restoring the capacity of bald mutants of S. tendae to erect aerial structures. Strikingly, a member (SC3) of the hydrophobin family of fungal proteins involved in the erection of aerial hyphae in the filamentous fungus Schizophyllum commune was also capable of restoring the capacity of S. coelicolor and S. tendae bald mutants to erect aerial structures. SC3 is unrelated in structure to SapB and streptofactin but, like the streptomycetes proteins, the fungal protein is a surface active agent. Scanning electron microscopy revealed that aerial structures produced in response to both the bacterial or the fungal proteins were undifferentiated vegetative hyphae that had grown away from the colony surface but had not commenced the process of spore formation. We conclude that the production of SapB and streptofactin at the start of morphological differentiation contributes to the erection of aerial hyphae by decreasing the surface tension at the colony surface but that subsequent morphogenesis requires additional developmentally regulated events under the control of bald genes.
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  • 2
    ISSN: 1365-3083
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The splenic mononuclear cells (MNC) of rabbits 7-14 and 30-48 days following primary intravenous immunization with sheep erythrocytes generated large numbers of antibody-secreting or plaque-forming cells (PFC) in secondary immune responses induced in vitro, whereas the splenic MNC obtained from rabbits 18-30 days following primary intravenous immunization generated poor secondary immune responses (few PFC) in vitro. However, these latter splenic MNC depleted of T cells consistently generated many PFC in the secondary immune response in vitro. Furthermore, the splenic MNC of rabbits thymectomized prior to day 3 following primary intravenous immunization also generated good secondary immune responses in vitro, irrespective of the time of killing post-immunization, whereas the splenic MNC of rabbits thymectomized after day 7 following primary immunization generated poor secondary immune responses in vitro. These results indicate that the depressed ability of the splenic MNC, obtained from rabbits killed between days 18 and 30 post-primary immunization, to generate significant secondary immune responses in vitro is due to suppressor T cells. The suppressor cells are referred to as immune spleen suppressor cells or ISSC. It was demonstrated that the suppression by the ISSC is antigen-specific and that the ISSC secrete an antigen-specific suppressor factor referred to as immune spleen suppressor factor or ISSF. It is concluded that the ISSC are generated in the thymus within a few days following primary immunization, that they migrate to and infiltrate the spleen between days 3 and 7 following primary immunization, and that they suppress or down-regulate further antibody synthesis via the secretion, locally of ISSF.
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  • 3
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Emissions of N2O were measured during the growth season over a year from grass swards under ambient (360 μL L−1) and elevated (600 μL L−1) CO2 partial pressures at the Free Air Carbon dioxide Enrichment (FACE) experiment, Eschikon, Switzerland. Measurements were made following high (56 g N m−2 yr−1) and low (14 g N m−2 yr−1) rates of fertilizer application, split over 5 re-growth periods, to Lolium perenne, Trifolium repens and mixed Lolium/Trifolium swards. Elevated pCO2 increased annual emissions of N2O from the high fertilized Lolium and mixed Lolium/Trifolium swards resulting in increases in GWP (N2O emissions) of 179 and 111 g CO2 equivalents m−2, respectively, compared with the GWP of ambient pCO2 swards, but had no significant effect on annual emissions from Trifolium monoculture swards. The greater emissions from the high fertilized elevated pCO2Lolium swards were attributed to greater below-ground C allocation under elevated pCO2 providing the energy for denitrification in the presence of excess mineral N. An annual emission of 959 mg N2O-N m−2 yr−1 (1.7% of fertilizer N applied) was measured from the high fertilized Lolium sward under elevated pCO2. The magnitude of emissions varied throughout the year with 84% of the total emission from the elevated pCO2Lolium swards measured during the first two re-growths (April–June 2001). This was associated with higher rainfall and soil water contents at this time of year. Trends in emissions varied between the first two re-growths (April–June 2001) and the third, fourth and fifth re-growths (late June–October 2000), with available soil NO3− and rainfall explaining 70%, and soil water content explaining 72% of the variability in N2O in these periods, respectively. Caution is therefore required when extrapolating from short-term measurements to predict long-term responses to global climate change. Our findings are of global significance as increases in atmospheric concentrations of CO2 may, depending on sward composition and fertilizer management, increase greenhouse gas emissions of N2O, thereby exacerbating the forcing effect of elevated CO2 on global climate. Our results suggest that when applying high rates of N fertilizer to grassland systems, Trifolium repens swards, or a greater component of Trifolium in mixed swards, may minimize the negative effect of continued increasing atmospheric CO2 concentrations on global warming.
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