Serum Response Factor Regulates Immediate Early Host Gene Expression in Toxoplasma gondii-Infected Host Cells

Toxoplasma gondii is a wide spread pathogen that can cause severe and even fatal disease in fetuses and immune-compromised hosts. As an obligate intracellular parasite, Toxoplasma must alter the environment of its host cell in order to establish its replicative niche. This is accomplished, in part, by secretion of factors into the host cell that act to modulate processes such as transcription. Previous studies demonstrated that genes encoding transcription factors such as c-jun, junB, EGR1, and EGR2 were amongst the host genes that were the most rapidly upregulated following infection. In cells stimulated with growth factors, these genes are regulated by a transcription factor named Serum Response Factor. Serum Response Factor is a ubiquitously expressed DNA binding protein that regulates growth and actin cytoskeleton genes via MAP kinase or actin cytoskeletal signaling, respectively. Here, we report that Toxoplasma infection leads to the rapid activation of Serum Response Factor. Serum Response Factor activation is a Toxoplasma-specific event since the transcription factor is not activated by the closely related protozoan parasite, Neospora caninum. We further demonstrate that Serum Response Factor activation requires a parasite-derived secreted factor that signals via host MAP kinases but independently of the host actin cytoskeleton. Together, these data define Serum Response Factor as a host cell transcription factor that regulates immediate early gene expression in Toxoplasma-infected cells

Photochemical production of ammonium in the oligotrophic Cyprus Gyre (Eastern Mediterranean)

International audienceWe investigated the photoproduction of ammonium (NH4+) in surface waters of the Cyprus gyre in the central Eastern Mediterranean in May 2002, in 8 on deck irradiations with freshly collected, filtered samples. NH4+ photoproduction (photoammonification) increased with time-integrated irradiance during the course of irradiations. Photoammonification rates around local noon were 0.4?2.9 nmol L?1 h?1. Normalised to time integrated irradiance, these rates were 0.9?3.8 pmol L?1 h?1/(W m?2) and were significantly correlated with Chromophoric Dissolved Organic Matter (CDOM) absorbance at 300 nm normalised to Dissolved Organic Carbon (DOC). These results are consistent with the notion that successive CDOM photobleaching in the surface mixed layer results in decreased DOC-normalised light absorbance concurrent with decreased dissolved organic matter reactivity with regard to photochemical NH4+ release. Combining our experimental data with estimates of annual solar irradiance and water column light attenuation yields an annual photoammonification rate for the Cyprus Gyre of 40±17 mmol m?2 a?1, equivalent to ~12±5% of the previously estimated annual nitrogen requirement of new production in this region. Based on this analysis, NH4+ photoproduction makes a small, but significant contribution to the nitrogen budget of the euphotic zone in the oligotrophic Cyprus Gyre

Determination of dissolved organic carbon in seawater using high temperature catalytic oxidation techniques

The high temperature catalytic oxidation (HTCO)-discrete injection method for liquid samples is currently the preferred analytical technique for the determination of dissolved organic carbon (DOC) in natural water samples. This approach yields equivalent or greater amounts of DOC than wet chemical oxidation methods, is suitable for routine analyses and is stable for shipboard determinations. However, a limited understanding of evaluation criteria for instrument performance presents a number of analytical challenges. This article discusses current practical problems encountered in the (i) collection and handling, (ii) preservation, (iii) decarbonation and (iv) analysis of seawater samples and reviews recent improvements in HTCO systems. Particular reference is made to the issue of certified reference materials and the oxidation efficiency of the technique. Copyright (C) 2000 Elsevier Science B.V

Effect of P and N addition to oligotrophic Eastern Mediterranean waters influenced by near-shore waters: A microcosm experiment

Phosphate (P), nitrate (N) or P+N added in a microcosm experiment to oligotrophic waters of the Eastern Mediterranean influenced by near-shore waters triggered a range of responses in the autotrophic and heterotrophic compartments of the system. Chlorophyll a increased in all treatments, including the no-addition control, implying that nutrients became available also from internal sources (recycling). Larger and faster biomass increase as well as a larger P utilization took place in the P+N treatments. Diatoms bloomed in the P+N treatments whereas coccolithophores bloomed following the addition of P ultimately reaching N-limitation. Bacterial activity responded with a transient peak to both low P-alone and N-alone additions (0.01 and 1 mu M, respectively). For reasons not well understood, no such response was observed at higher P-alone additions (0.05 and 0.5 mu M), whereas at the two highest P+N additions the positive response was delayed. We therefore were unable to conclude conclusively on bacteria] limitation. In most cases, the increase in bacterial activity was not matched by an increase in abundance, suggesting a tight top-down control of the biomass. Instead, heterotrophic nanoflagellate and ciliate abundances increased in all treatments. A slightly elevated orthophosphate turnover-time (T-t) (32h) in the initial waters did not give a clear indication of P-limitation, although the system could absorb the lowest P-addition (0.01 mu M) without increase in T-t N alone lead to a reduction in T-t as would be expected in an N-limited system consuming existing surplus P after N-addition. The response of the near-shore influenced system used in this study was in accord with the `classical' response to nutrient introduction-increase in chlorophyll a and in large size phytoplankton. In contrast, in the ultraoligotrophic Cyprus Eddy [Krom, Thingstad, Carbo, Drakopoulos, Fileman, Flaten, Groom, Herut, Kitides, Kress, Law, Liddicoact, Mantoura, Pasternak, Pitta, Polychronaki, Psarra, Rassoulzadegan, Skjoldal, Spyres, Tanaka, Tselepides, Wassmann, Wexels-Riser, Woodward, Zodiatis, Zohary, 2005. Overview of the CYCLOPS P addition lagrangian experiment in the Eastern Mediterranean. Deep-Sea Research II, this volume.], the short T, (< 4h) indicated P-limitation, the combined addition of P and N (as ammonium) induced a bloom of picocyanobacteria [Zohary, Herut, Krom, Mantoura, Pitta, Psarra, Rasssoulzadegan, Stambler, Tanaka, Thingstad, Woodward, 2005. P-limited bacteria but N&P co-limited phytoplankton in the Eastern Mediterranean-a microcosm experiment. Deep-Sea Research II, this volume.] and the in situ P alone addition led to a decrease in chlorophyll. (c) 2005 Elsevier Ltd. All rights reserved