Characterization of phytoplankton assemblages in a tropical coastal environment using Kohonen self‐organizing map

This study was aimed at understanding the main abiotic environmental factors controlling the distribution patterns of abundance and composition of phytoplankton (size less than 10 μm) assemblages in the coastal waters of south‐eastern Côte d'Ivoire. Data were collected during two cruises, in January (low‐water period) and October (high‐water period) of 2014. A total of 67 species were identified and assigned to Bacillariophyceae (49%), Cyanophyceae (21%), Chlorophyceae (13%), Euglenophyceae (10%), Dinophyceae (4%) and Chrysophyceae (3%). Three biotic zones (I, IIA and IIB) were distinguishable on a Kohonen self‐organizing map after an unsupervised learning process. The diatom genera Eunotia sp., Navicula sp. and Actinoptychus senarius are significantly associated with I, IIA and IIB biotic zones, respectively. A clear seasonal cum salinity trend was apparent in phytoplankton distribution patterns. Turbidity and nitrate levels were the main abiotic factors controlling phytoplankton distribution in I, the upland tidal regions of the lagoon. In regions along the lagoon–sea continuum, phosphate and turbidity exert the most control during the low‐water season (IIA), while total dissolved solids control phytoplankton distribution during the high‐water season (IIB). These are climate‐sensitive parameters whose concentrations depend on prevailing hydroclimatic processes. Therefore, seasonality can have important consequences on phytoplankton community and inadvertently the productivity of these systems.     

No Evidence for Adaptive Micro-Evolution to a Decrease in Phosphorus-Loading of a Daphnia Population Inhabiting A Pre-Alpine Lake

Many polluted lakes in Europe are being restored and phosphorus concentrations have dropped dramatically in these lakes. We studied the genetic structure of Daphnia galeata over the past 30 years in Lake Greifensee, Switzerland, a period during which the phosphorus concentration in the lake reduced dramatically. Distinct genotypes of D. galeata were hatched from diapausing eggs extracted from six different time horizons in dated sediments. We compared juvenile growth, size and egg production of D. galeata reared on high-P and low-P algae to investigate whether Daphnia have evolved to grow better on phosphorus-limited algae. Our results indicate that life histories of D. galeata differed significantly between both food types. We also found significant clone effects for size and egg number. But we found no significant interaction between the depth from which the clones were selected and food quality. This means that we found no evidence for adaptive micro-evolution in response to P reduction in the lake. We discuss our results in relation to other studies that found evidence for adaptive micro-evolution in comparable time frames.     

INFLUENCE OF CERTAIN PLANT GROWTH REGULATORS AND CROWN-GALL RELATED SUBSTANCES ON BUD FORMATION AND GAMETOPHORE DEVELOPMENT OF THE MOSS PYLAISIELLA SELWYNII

Bud formation and gametophore development were studied in the moss Pylaisiella selwynii (Kindb.) Steere and Anderson grown from spores in a liquid medium consisting of inorganic salts. Indoleacetic acid and ethrel increased bud formation within a narrow concentration range. Copious bud formation was obtained with the five cytokinins tested at concentrations varying from 5 X 10⁻⁶ to 5 X 10⁻¹⁴ M. Except for about 10 % of the buds obtained with 6-γ, γ-dimethylallylaminopurine at 5 times 10⁻¹⁴ m, the cytokinin-induced buds failed to develop into normal gametophores. Octopine, lysopine, and octopinic acid, substances obtained from crown-gall tumors, increased bud formation at 10⁻³ m. On lysopine-treated plants these buds developed into typical gametophores. Gemma-like structures were obtained with octopine but no gametophores. l -arginine and l -lysine, the amino acids which respectively occur in octopine and lysopine, failed to induce gametophore formation although buds were obtained with 10⁻³ m lysine. γ-Guanidinobutyric acid induced bud formation at 10⁻³ m, but these buds developed into highly abnormal gametophores. The failure of buds obtained with many of these treatments to develop into gametophores appeared to result from the formation of new cell walls in other than the normal geometrical relationship during initial divisions of the pro-bud. The relevance of the findings to the crown-gall problem is discussed.     

How Much Is Too Little to Detect Impacts? A Case Study of a Nuclear Power Plant

Several approaches have been proposed to assess impacts on natural assemblages. Ideally, the potentially impacted site and multiple reference sites are sampled through time, before and after the impact. Often, however, the lack of information regarding the potential overall impact, the lack of knowledge about the environment in many regions worldwide, budgets constraints and the increasing dimensions of human activities compromise the reliability of the impact assessment. We evaluated the impact, if any, and its extent of a nuclear power plant effluent on sessile epibiota assemblages using a suitable and feasible sampling design with no ‘before’ data and budget and logistic constraints. Assemblages were sampled at multiple times and at increasing distances from the point of the discharge of the effluent. There was a clear and localized effect of the power plant effluent (up to 100 m from the point of the discharge). However, depending on the time of the year, the impact reaches up to 600 m. We found a significantly lower richness of taxa in the Effluent site when compared to other sites. Furthermore, at all times, the variability of assemblages near the discharge was also smaller than in other sites. Although the sampling design used here (in particular the number of replicates) did not allow an unambiguously evaluation of the full extent of the impact in relation to its intensity and temporal variability, the multiple temporal and spatial scales used allowed the detection of some differences in the intensity of the impact, depending on the time of sampling. Our findings greatly contribute to increase the knowledge on the effects of multiple stressors caused by the effluent of a power plant and also have important implications for management strategies and conservation ecology, in general.     

The SANT2 domain of the murine tumor cell DnaJ-like protein 1 human homologue interacts with alpha1-antichymotrypsin and kinetically interferes with its serpin inhibitory activity

The murine tumor cell DnaJ-like protein 1 or MTJ1/ERdj1 is a membrane J-domain protein enriched in microsomal and nuclear fractions. We previously showed that its lumenal J-domain stimulates the ATPase activity of the molecular chaperone BiP/GRP78 (Chevalier, M., Rhee, H., Elguindi, E. C., and Blond, S. Y. (2000) J. Biol. Chem. 275, 19620-19627). MTJ1/ERdj1 also contains a large carboxyl-terminal cytosolic extension composed of two tryptophan-mediated repeats or SANT domains for which the function(s) is unknown. Here we describe the cloning of the human homologue HTJ1 and its interaction with alpha(1)-antichymotrypsin (ACT), a member of the serine proteinase inhibitor (serpin) family. The interaction was initially identified in a two-hybrid screening and further confirmed in vitro by dot blots, native electrophoresis, and fluorescence studies. The second SANT domain of HTJ1 (SANT2) was found to be sufficient for binding to ACT, both in yeast and in vitro. Single tryptophan-alanine substitutions at two strictly conserved residues significantly (Trp-497) or totally (Trp-520) abolished the interaction with ACT. SANT2 binds to human ACT with an intrinsic affinity equal to 0.5 nm. Preincubation of ACT with nearly stoichiometric concentrations of SANT2 wild-type but not SANT2: W520A results in an apparent loss of ACT inhibitory activity toward chymotrypsin. Kinetic analysis indicates that the formation of the covalent inhibitory complex ACT-chymotrypsin is significantly delayed in the presence of SANT2 with no change on the catalytic efficiency of the enzyme. This work demonstrates for the first time that the SANT2 domain of MTJ1/HTJ1/ERdj1 mediates stable and high affinity protein-protein interactions.     

The complexities of G-protein-coupled receptor kinase function in Hedgehog signaling

Hedgehog (Hh) signaling is essential for proper tissue patterning and maintenance and has a substantial impact on human disease. While many of the main components and mechanisms involved in transduction of the Hh signal have been identified, the details of how the pathway functions are continually being refined. One aspect that has attracted much attention recently is the involvement of G-protein-coupled receptor kinases (GRKs) in the pathway. These regulators of G-protein-coupled receptor (GPCR) signaling have an evolutionarily-conserved function in promoting high-threshold Hh target gene expression through regulation of Smoothened (Smo), a GPCR family member that activates intracellular Hh signaling. Several models of how GRKs impact on Smo to increase downstream signaling have been proposed. Recently, we demonstrated that these kinases have surprisingly complex and conflicting roles, acting to limit signaling through the pathway while also promoting Smo activity. In addition to the previously described direct effects of Gprk2 on Smo activation, Gprk2 also indirectly affects Hh signaling by controlling production of the second messenger cyclic AMP to influence Protein kinase A activity.     

Mitochondrial haplotypes reveal olive fly (Bactrocera oleae) population substructure in the Mediterranean

The olive fly (Bactrocera oleae) is the most important olive tree (Olea europaea) pest. In the Mediterranean basin, where 98?% of its main hosts are concentrated, it causes major agricultural losses, due to its negative effect on production and quality of both olive and olive oil. Previous phylogeographic analyses have established that Mediterranean olive fly populations are distinct from other Old World populations, but did not agree on the specific population substructure within this region. In order to achieve a higher resolution of the diversity of olive fly populations, particularly in Central and Western Mediterranean (home to 70?% of the world production), we comparatively analyzed a set of samples from Portugal in the context of published mitochondrial sequences across the species' worldwide range. Strong evidence of population substructure was found in the Central and Western Mediterranean area, with two clearly separate phylogenetic branches. Together with previously published data, our results strongly support the existence of at least three distinct Mediterranean populations of the olive fly, raise the possibility of additional regional substructure and suggest specific avenues for future research. This knowledge can be instrumental in the development of better management and control strategies for a major pest of Mediterranean agriculture.     

An Extracellular Ion Pathway Plays a Central Role in the Cooperative Gating of a K2P K+ Channel by Extracellular pH

Proton-gated TASK-3 K⁺ channel belongs to the K_2P family of proteins that underlie the K⁺ leak setting the membrane potential in all cells. TASK-3 is under cooperative gating control by extracellular [H⁺]. Use of recently solved K_2P structures allows us to explore the molecular mechanism of TASK-3 cooperative pH gating. Tunnel-like side portals define an extracellular ion pathway to the selectivity filter. We use a combination of molecular modeling and functional assays to show that pH-sensing histidine residues and K⁺ ions mutually interact electrostatically in the confines of the extracellular ion pathway. K⁺ ions modulate the pK_a of sensing histidine side chains whose charge states in turn determine the open/closed transition of the channel pore. Cooperativity, and therefore steep dependence of TASK-3 K⁺ channel activity on extracellular pH, is dependent on an effect of the permeant ion on the channel pH_o sensors.