Combined toxicity of graphite-diamond nanoparticles and thiabendazole to Daphnia magna

Carbon-based nanomaterials exhibit unique properties that make them suitable for a wide variety of industrial and biomedical applications. In this work, we studied the acute toxicity of graphite-diamond nanoparticles (GDN) combined with the fungicide thiabendazole (TBZ) to the immobilization of the cladoceran Daphnia magna in the presence and absence of the micro green algae Raphidocelis subcapitata, supplied as food source. The toxicity of GDN to D. magna decreased in the presence of R. subcapitata, while that of TBZ increased, the latter suggesting a carrier effect to TBZ. GDN-TBZ mixtures were fitted to the most common conceptual models applied to mixture toxicity: Concentration Addition (CA), Independent Action (IA) and Combination Index (CI). For GDN-TBZ mixtures in the absence of food the best fit was obtained with dose ratio deviation from CA model, while in the presence of food, dose level deviation from CA gave a better fit. The binary mixtures of GDN and TBZ showed synergistic toxic interactions at low concentrations, which could be attributed to the increased bioavailability of TBZ adsorbed on GDN. For higher concentrations of GDN, the binary mixtures turned antagonistic due to particle agglomeration. Our study provides evidence that deviations from additivity are dose dependent and relevant for the risk assessment of mixtures of nanoparticles with other chemical pollutants.publishe

The small Ca2+-binding protein CSE links Ca2+ signalling with nitrogen metabolism and filament integrity in Anabaena sp. PCC 7120

Background Filamentous cyanobacteria represent model organisms for investigating multicellularity. For many species, nitrogen-fixing heterocysts are formed from photosynthetic vegetative cells under nitrogen limitation. Intracellular Ca2+ has been implicated in the highly regulated process of heterocyst differentiation but its role remains unclear. Ca2+ is known to operate more broadly in metabolic signalling in cyanobacteria, although the signalling mechanisms are virtually unknown. A Ca2+-binding protein called the Ca2+ Sensor EF-hand (CSE) is found almost exclusively in filamentous cyanobacteria. Expression of asr1131 encoding the CSE protein in Anabaena sp. PCC 7120 was strongly induced by low CO2 conditions, and rapidly downregulated during nitrogen step-down. A previous study suggests a role for CSE and Ca2+ in regulation of photosynthetic activity in response to changes in carbon and nitrogen availability. Results In the current study, a mutant Anabaena sp. PCC 7120 strain lacking asr1131 (Delta cse) was highly prone to filament fragmentation, leading to a striking phenotype of very short filaments and poor growth under nitrogen-depleted conditions. Transcriptomics analysis under nitrogen-replete conditions revealed that genes involved in heterocyst differentiation and function were downregulated in Delta cse, while heterocyst inhibitors were upregulated, compared to the wild-type.Conclusions These results indicate that CSE is required for filament integrity and for proper differentiation and function of heterocysts upon changes in the cellular carbon/nitrogen balance. A role for CSE in transmitting Ca2+ signals during the first response to changes in metabolic homeostasis is discussed.</div

A third genetic locus required for the formation of heterocysts in Anabaena sp. strain PCC 7120.

Mutagenesis of Anabaena sp. strain PCC 7120 with a derivative of transposon Tn5 led to the isolation of a mutant strain, P6, in which heterocysts are not formed (A. Ernst, T. Black, Y. Cai, J.-M. Panoff, D. N. Tiwari, and C. P. Wolk, J. Bacteriol. 174:6025-6032, 1992). Reconstruction of the transposon mutation of P6 in the wild-type strain reproduced the phenotype of the original mutant. Analysis by pulsed-field gel electrophoresis localized the transposition at ca. 3.44 Mb on the physical map of the chromosome of wild-type Anabaena sp. The transposon was situated within an open reading frame (ORF), which we denote hetP, whose wild-type form was cloned and also sequenced. The predicted HetP protein was not found to show significant sequence similarity to other proteins. The mutation in strain P6 could be complemented by a clone of a fragment of wild-type DNA that includes hetP and at least one additional ORF 3' from hetP, but not by a clone that includes hetP as its only ORF. The latter clone proved highly toxic. The phenotype of the P6 mutant may, therefore, be due to a polar effect of the insertion of the transposon. Filaments of strain P6 and of the wild-type strain, when bearing the complementing fragment on a pDU1-based plasmid, showed an increased frequency of clustered heterocysts compared with that of the wild-type strain

Hypochlorite Scavenging Activity Of Cerium Oxide Nanoparticles

In this report, we provide evidence that specific synthesis of cerium oxide nanoparticles can scavenge the hypochlorite anion, which is a strong extracellular oxidant involved in the inflammatory processes. The scavenging process takes place by a surface reaction involving the evolution of oxygen and the reduction of Ce4+ to Ce3+

On the role of ultrasound and mechanical stirring for iodide adsorption by calcined layered double hydroxides

[EN]Improving the adsorption of long-term radioactive species in the underground disposal of waste waters from nuclear reactors is a key issue. The natural metal oxides or hydroxides underground have the low retention ability of anionic species. Here, calcined Mg/Al LDHs were used as adsorbents. The influence on the adsorption capacity of different intercalated guest anions (carbonate (CO32-) and nitrate (NO3-)) in the parent LDH was investigated, along with the effect of ultrasonication. Two Mg/Al molar ratios (3/1 and 2/1) were compared. Adsorption capacity was strongly affected by material textural properties, and the carbonate LDH-derived mixed oxides showed the largest adsorption capacity. Mixed oxides with an Mg/Al molar ratio equal to 3 presented higher iodide adsorption due to their lower charge density. The adsorption assisted by ultrasound increased iodide removal efficiency by reducing internal diffusion limitation. Two models were used to determine adsorption capacity: Langmuir and Freundlich. The iodide adsorption was best fitted by the Langmuir equilibrium model

On the role of ultrasound and mechanical stirring for iodide adsorption by calcined layered double hydroxides.

10.1016/j.clay.2014.02.012Improving the adsorption of long-term radioactive species in the underground disposal of waste waters from nuclear reactors is a key issue. The natural metal oxides or hydroxides underground have the low retention ability of anionic species. Here, calcined Mg/Al LDHs were used as adsorbents. The influence on the adsorption capacity of different intercalated guest anions (carbonate (CO32 -) and nitrate (NO3-)) in the parent LDH was investigated, along with the effect of ultrasonication. Two Mg/Al molar ratios (3/1 and 2/1) were compared. Adsorption capacity was strongly affected by material textural properties, and the carbonate LDH-derived mixed oxides showed the largest adsorption capacity. Mixed oxides with an Mg/Al molar ratio equal to 3 presented higher iodide adsorption due to their lower charge density. The adsorption assisted by ultrasound increased iodide removal efficiency by reducing internal diffusion limitation. Two models were used to determine adsorption capacity: Langmuir and Freundlich. The iodide adsorption was best fitted by the Langmuir equilibrium model

Spatial and temporal heterogeneity in succession of cyanobacterial blooms in a Spanish reservoir

We describe here the limnological characteristics of the Santillana Reservoir (Spain) and study the phytoplankton distribution during a typical growing season (July to November). The reservoir is a eutrophic stratified waterbody in central part of Spain, in which the average phytoplankton biomass in summer is higher than 20 µg chlorophyll a 1-1. Maximum phytoplankton biomass in 1999 occurred between the end of summer and the beginning of autumn (September-October). Cyanobacteria, that were generally prevalent in phytoplankton community, clearly dominated during the peak of phytoplankton biomass. Microcystis wesenbergii was dominant amongst the cyanobacteria and represented almost 100 % of the biomass at the time of maximum phytoplankton value. The importance of environmental variables triggering cyanobacterial bloom events is discussed. Our results indicate that neither temperature nor N/P ratio are related to the bloom development. However, high nutrient concentration (ammonium in particular) and stability of the watercolumn seems to coincide with the maximum abundance of Microcystis wesenbergii

A novel Ca 2+-binding protein influences photosynthetic electron transport in Anabaena sp. PCC 7120

Ca2+ is a potent signalling molecule that regulates many cellular processes. In cyanobacteria, Ca2+ has been linked to cell growth, stress response and photosynthesis, and to the development of specialist heterocyst cells in certain nitrogen-fixing species. Despite this, the pathways of Ca2+ signal transduction in cyanobacteria are poorly understood, and very few protein components are known. The current study describes a previously unreported Ca2+-binding protein which was called the Ca2+ Sensor EF-hand (CSE), which is conserved in filamentous, nitrogen-fixing cyanobacteria. CSE is shown to bind Ca2+, which induces a conformational change in the protein structure. Poor growth of a strain of Anabaena sp. PCC 7120 overexpressing CSE was attributed to diminished photosynthetic performance. Transcriptomics, biophysics and proteomics analyses revealed modifications in the light-harvesting phycobilisome and photosynthetic reaction centre protein complexes