Climate change effects on phytoplankton depend on cell size and food web structure

We investigated the effects of warming on a natural phytoplankton community from the Baltic Sea, based on six mesocosm experiments conducted 2005–2009. We focused on differences in the dynamics of three phytoplankton size groups which are grazed to a variable extent by different zooplankton groups. While small-sized algae were mostly grazer-controlled, light and nutrient availability largely determined the growth of medium- and large-sized algae. Thus, the latter groups dominated at increased light levels. Warming increased mesozooplankton grazing on medium-sized algae, reducing their biomass. The biomass of small-sized algae was not affected by temperature, probably due to an interplay between indirect effects spreading through the food web. Thus, under the higher temperature and lower light levels anticipated for the next decades in the southern Baltic Sea, a higher share of smaller phytoplankton is expected. We conclude that considering the size structure of the phytoplankton community strongly improves the reliability of projections of climate change effects

Experimental study on the microbial plankton community in a South American wetland (Lower Paraná River Basin) and the effect of the light deficiency due to the floating macrophytes

An experimental study using microcosms was conducted in a South American wetland, Lower Paraná River Basin (Argentina), to analyse the structure of the components of the microbial plankton community and the influence of the light deficiency due to floating macrophytes on this community. Two experiments were run under different light conditions; the decrease of the light penetration due to floating macrophytes was simulated using different nylon mesh covers that resembled natural conditions in the lake. These studies revealed that the light deficiency favoured the replacement of obligate autotrophs by mixotrophic and heterotrophic organisms. Abundances of strictly autotrophic algae along the experiments responded to the light gradient, being maximum in the flasks without cover. Heterotrophic nanoflagellates (HNF) and ciliates increased in the microcosms, probably favoured by the high food availability (picoplankton) and the lack of their predators (zooplankton). The increase of ciliates was higher in the microcosms with more light. In the first experiment, the picoplankton fraction strongly decreased after 24 h in the flasks that included all their potential predators, thus suggesting a grazing pressure on this fraction. Grazing experiments performed with fluorescent-labelled bacteria (FLB) revealed that two Cryptomonas species, which are frequent in the lake (Cryptomonas erosa and Cryptomonas marssonii), can ingest bacteria. © The Author 2006. Published by Oxford University Press. All rights reserved.Fil:Sinistro, R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Izaguirre, I. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Experimental study of the zooplankton impact on the trophic structure of phytoplankton and the microbial assemblages in a temperate wetland (Argentina)

An experimental study using mesocosms was conducted in the main shallow lake of a temperate wetland (Otamendi Natural Reserve, Argentina) to analyse the impact of zooplankton on phytoplankton and the microbial assemblages. The lake is characterised by the presence of a fluctuating cover of floating macrophytes, whose shading effects shape the phytoplakton community and the ecosystem functioning, which was absent during the study period. The experiment was run in situ using polyethylene bags, comparing treatments with and without zooplankton. The cascade effect of zooplankton on phytoplankton and the lower levels of the microbial food web (ciliates, heterotrophic nanoflagellates (HNF) and picoplankton) were analysed. A significant zooplankton grazing on the nano-phytoplankton fraction (3-30 μm) was observed. Conversely, large algae (filamentous cyanobacteria, colonial chlorophytes and large diatoms) increased in all mesocosms until day 10, suggesting that they were not actively grazed by zooplankton during this period. However, from day 10 until day 17 this fraction decreased in the enclosures with mesozooplankton, probably due to an increase in the abundance of large herbivores. The results of the experiment would also indicate a trophic cascade effect on the lower levels of the microbial community. In the treatment where zooplankton was removed, the abundance of ciliates followed the same increasing pattern as the abundance of HNF, but with a time lag in its response. In the enclosures without zooplankton, HNF remained relatively constant throughout the experiment, whereas ciliates strongly decrease during the last week. Total picoplankton abundance increased in the enclosures with mesozooplankton, thus supporting the existence of a four-link trophic cascade (copepods-microzooplankton-HNF-picoplankton). Zooplankton composition changed significantly from the beginning until the end of the experiment; cyclopoid nauplii and rotifers were notoriously dominant at t0, whereas 10 days later the community showed a more equitable proportion of cyclopoids, calanoids, nauplii, cladocerans and rotifers. © 2006 Elsevier GmbH. All rights reserved.Fil:Sinistro, R. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Sánchez, M.L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Izaguirre, I. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Vitamin D3 modulates T lymphocyte responses in hepatitis C virus-infected liver transplant recipients.

BACKGROUND: Aim of the present study was to investigate whether 1,25(OH)(2)D(3) (Vitamin D3) modulates T lymphocyte functions in patients transplanted for hepatitis C virus-related cirrhosis. METHODS: Sixteen patients and ten healthy subjects were investigated. T lymphocytes were activated in vitro in the presence or absence of Vitamin D3 and then the proliferative response and IFN-γ and TNF-α production were assessed. RESULTS: Vitamin D3 potently reduced T-lymphocyte proliferation in a dose-related fashion. Similarly, FACS analysis and ELISA testing demonstrated that Vitamin D3 significantly decreased the response frequency and the response intensity of IFN-γ and TNF-α production in the whole CD3-positive T lymphocyte population as well as in "naive" CD4+ CD45RA+ and "memory" CD4+ CD45RO+ T lymphocyte subsets. The inhibitory effect of Vitamin D3 on T-cell proliferation and cytokine production was not different between patients and controls. No toxic effects were exerted by Vitamin D3 even at the higher concentration used (10nM). Finally, no statistically significant correlation was found between 25(OH)D serum levels and the proliferative response or cytokine production of T lymphocytes from transplanted patients. CONCLUSIONS: This study demonstrates that in patients transplanted for hepatitis C virus-related cirrhosis Vitamin D3 modulates T lymphocyte activation, and provides a rationale for the evaluation of this compound as an immunosuppressive agent in liver-transplanted patients

Design, Molecular Modeling, Synthesis, and Anti-HIV-1 Activity of New Indolyl Aryl Sulfones. Novel Derivatives of the Indole-2-carboxamide

Molecular modeling studies and an updated highly predictive 3-D QSAR model led to the discovery of exceptionally potent indolyl aryl sulfones (IASs) characterized by the presence of either a pyrrolidyn-2-one nucleus at the indole-2-carboxamide or some substituents at the indole-2-carbohydrazide. Compounds 7 and 9 were found active in the sub-nanomolar range of concentration in both MT-4 and C8166 cell-based anti-HIV assays. These compounds, and in particular compound 9, also showed excellent inhibitory activity against both HIV-112 and HIV-AB1 primary isolates in lymphocytes and against HIV WT in macrophages

Indolyl Aryl Sulfones as HIV-1 Non-Nucleoside Reverse Transcriptase Inhibitors: Role of Two Halogen Atoms at the Indole Ring in Developing New Analogues with Improved Antiviral Activity

Indolyl aryl sulfones bearing the 4,5-difluoro (10) or 5-chloro-4-fluoro (16) substitution pattern at the indole ring were potent inhibitors of HIV-1 WT and the NNRTI-resistant strains Y181C and K103N-Y181C. These compounds were highly effective against the 112 and the AB1 strains in lymphocytes and inhibited at nanomolar concentration the multiplication of the IIIBBa-L strain in macrophages. Compound 16 was exceptionally potent against RT WT and RTs carrying the K103N, Y181I, and L100I mutations

Synthesis of Indol Aryl Sulfones bearing Natural and Unnatural Aminoacids as Potent HIV-1 Non-Nucleoside Reverse Transcriptase.

Comunicazione Poster P-10