Plant–soil feedback of native and range-expanding plant species is insensitive to temperature

Temperature change affects many aboveground and belowground ecosystem processes. Here we investigate the effect of a 5°C temperature increase on plant–soil feedback. We compare plant species from a temperate climate region with immigrant plants that originate from warmer regions and have recently shifted their range polewards. We tested whether the magnitude of plant–soil feedback is affected by ambient temperature and whether the effect of temperature differs between these groups of plant species. Six European/Eurasian plant species that recently colonized the Netherlands (non-natives), and six related species (natives) from the Netherlands were selected. Plant–soil feedback of these species was determined by comparing performance in conspecific and heterospecific soils. In order to test the effect of temperature on these plant–soil feedback interactions, the experiments were performed at two greenhouse temperatures of 20/15°C and 25/20°C, respectively. Inoculation with unconditioned soil had the same effect on natives and non-natives. However, the effect of conspecific conditioned soil was negative compared to heterospecific soil for natives, but was positive for non-natives. In both cases, plant–soil interactions were not affected by temperature. Therefore, we conclude that the temperature component of climate change does not affect the direction, or strength of plant–soil feedback, neither for native nor for non-native plant species. However, as the non-natives have a more positive soil feedback than natives, climate warming may introduce new plant species in temperate regions that have less soil-borne control of abundance

Protein secretion in the Archaea: multiple paths towards a unique cell surface

Archaea are similar to other prokaryotes in most aspects of cell structure but are unique with respect to the lipid composition of the cytoplasmic membrane and the structure of the cell surface. Membranes of archaea are composed of glycerol-ether lipids instead of glycerol-ester lipids and are based on isoprenoid side chains, whereas the cell walls are formed by surface-layer proteins. The unique cell surface of archaea requires distinct solutions to the problem of how proteins cross this barrier to be either secreted into the medium or assembled as appendages at the cell surface.

Predictors of trend in CD4-positive T-cell count and mortality among HIV-1-infected individuals with virological failure to all three antiretroviral-drug classes

Background Treatment strategies for patients in whom HIV replication is not suppressed after exposure to several drug classes remain unclear. We aimed to assess the inter-relations between viral load, CD4-cell count, and clinical outcome in patients who had experienced three-class virological failure. Methods We undertook collaborative joint analysis of 13 HIV cohorts from Europe, North America, and Australia, involving patients who had had three-class virological failure (viral load >1000 copies per mL for >4 months). Regression analyses were used to quantify the associations between CD4-cell-count slope, HIV-1 RNA concentration, treatment information, and demographic characteristics. Predictors of death were analysed by Cox's proportional-hazards models. Findings 2488 patients were included. 2118 (85%) had started antiretroviral therapy with single or dual therapy. During 5015 person-years of follow-up, 276 patients died (mortality rate 5.5 per 100 person-years; 3-year mortality risk 15.3% (95% Cl 13.5-17.3). Risk of death was strongly influenced by the latest CD4-cell count with a relative hazard of 15.8 (95% CI 9.28-27.0) for counts below 50 cells per muL versus above 200 cells per muL. The latest viral load did not independently predict death. For any given viral load, patients on treatment had more favourable CD4-cell-count slopes than those off treatment. For patients on treatment and with stable viral load, CD4-cell counts tended to be increasing at times when the current viral load was below 10 000 copies per mL or 1.5 log(10) copies per mL below off-treatment values. Interpretation In patients for whom viral-load suppression to below the level of detection is not possible, achievement and maintenance of a CD4-cell count above 200 per muL becomes the primary aim. Treatment regimens that maintain the viral load below 10 000 copies per mL or at least provide 1.5 log(10) copies per mL suppression below the off-treatment value do not seem to be associated with appreciable CD4-cell-count decline