Long-term variations of epilimnetic phytoplankton in an artificial reservoir during a 10-year survey

Vieux-Pré is an artificial reservoir in the north-east part of France (61 Mm³), created in 1986 for hydraulic management. The phytoplankton and several environmental parameters in the upper part of the lake were monitored at a mid-lake station, from 1988 to 1997. The specific composition of the community changed during this period, from a predominantly pennate-diatom phytoplankton (Asterionella formosa, Fragilaria crotonensis), the lake passed to dominance by a sparse, motile nanoplankton (Mallomonas akrokomos, M. caudata, Cryptomonas erosa, Chroomonas/Rhodomonas, a.o.) and then by large colonies of small-celled species (Uroglena americana, Dinobryon spp., Radiocystis geminata, Aphanothece clathrata, Coelosphaerium kuetzingianum a.o.). This paper describes the algal successions involved and shows the decisive effects of the decrease of trophic level from an eutrophic stage to an oligo-mesotrophic condition. In the beginning, externally imposed disturbances (flooding and dewatering) were frequent, while now the lake has stabilised as a deep, stratified pelagic system. Under these conditions, autogenic phytoplankton appear to dominate.     

Disturbance history influences the distribution of stream invertebrates by altering microhabitat parameters: a field experiment

1. We investigated the effects of local disturbance history and several biotic and abiotic habitat parameters on the microdistribution of benthic invertebrates after an experimental disturbance in a flood‐prone German stream. 2. Bed movement patterns during a moderate flood were simulated by scouring and filling stream bed patches (area 0.49 m²) to a depth of 15–20 cm. Invertebrates were investigated using ceramic tiles as standardized substrata. After 1, 8, 22, 29, 36 and 50 days, we sampled one tile from each of 16 replicates of three bed stability treatments (scour, fill and stable controls). For each tile, we also determined water depth, near‐bed current velocity, the grain size of the substratum beneath the tile, epilithic algal biomass and standing stock of particulate organic matter (POM). 3. Shortly after disturbance, total invertebrate density, taxon richness and density of the common taxa Baetis spp. and Chironomidae were highest in stable patches. Several weeks after disturbance, by contrast, Baetis spp. and Hydropsychidae were most common in fill and Leuctra spp. in scour patches. The black fly Simulium spp. was most abundant in fill patches from the first day onwards. Community evenness was highest in scour patches during the entire study. 4. Local disturbance history also influenced algal biomass and POM standing stock at the beginning of the experiment, and water depth, current velocity and substratum grain size throughout the experiment. Scouring mainly exposed finer substrata and caused local depressions in the stream bed characterized by slower near‐bed current velocity. Algal biomass was higher in stable and scour patches and POM was highest in scour patches. In turn, all five common invertebrate taxa were frequently correlated with one or two of these habitat parameters. 5. Our results suggest that several ‘direct’ initial effects of local disturbance history on the invertebrates were subsequently replaced by ‘indirect’ effects of disturbance history (via disturbance‐induced changes in habitat parameters such as current velocity or food).     

Self-Diffusion in Electrostatically Stabilized Colloidal Suspensions Using Brownian Dynamics

Abstract

Brownian dynamics is applied to suspended colloidal particles interacting through a screened Coulombic pair potential in the dilute region where the hydrodynamics is approximated by Stokes drag. Calculated properties include the osmotic pressure, the radial distribution function, and the self-diffusion coefficient. Verification is obtained by comparing the results to independently evaluated properties. Self-diffusion coefficicents are compared to approximate theories in the literature. The self-diffusion coefficient is observed to depend strongly on the local structure but only slightly on the longer range structure.     

Molecular dynamics simulations of the thermal stability of tteRBP and ecRBP

Molecular dynamics simulations were performed for investigating the thermal stability of the extremely thermophilic Thermoanaerobacter tengcongensis ribose binding protein (tteRBP) and the mesophilic homologous Escherichia coli ribose binding protein (ecRBP). The simulations for the two proteins were carried out under the room temperature (300?K) and the optimal activity temperature (tteRBP 375?K and ecRBP 329?K), respectively. The comparative analyses of the trajectories show that the two proteins have stable overall structures at the two temperatures; further analyses indicate that they both have strong side-chain interactions and different backbone flexibilities at the different temperatures. The tteRBP 375?K and ecRBP 329?K have stronger internal motion and higher flexibility than tteRBP 300?K and ecRBP 300?K, respectively, it is noted that the flexibility of tteRBP is much higher than that of ecRBP at the two temperatures. Therefore, tteRBP 375?K can adapt to high temperature due to its higher flexibility of backbone. Combining with the researches by Cuneo et al., it is concluded that the side-chain interactions and flexibility of backbone are both the key factors to maintain thermal stability of the two proteins.

An animated Interactive 3D Complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:22     

The effects of pollen,propolis, and caffeic acid phenethyl ester on tyrosine hydroxylase activity and total RNA levels in hypertensive rats caused by nitric oxide synthase inhibition: experimental,docking and molecular dynamic studies

The objective of the present study was to evaluate the effects of propolis, pollen, and caffeic acid phenethyl ester (CAPE) on tyrosine hydroxylase (TH) activity and total RNA levels of Nω-nitro-L-arginine methyl ester (L-NAME) inhibition of nitric oxide synthase in the heart, adrenal medulla, and hypothalamus of hypertensive male Sprague dawley rats. The TH activity in the adrenal medulla, heart, and hypothalamus of the rats was significantly increased in the L-NAME group vs. control (p < 0.05). Treatment with L-NAME led to a significant increase in blood pressure (BP) in the L-NAME group compared to control (p < 0.05). These data suggest that propolis, pollen, and CAPE may mediate diminished TH activity in the heart, adrenal medulla, and hypothalamus in hypertensive rats. The decreased TH activity may be due to the modulation and synthesis of catecholamines and BP effects. In addition, the binding mechanism of CAPE within the catalytic domain of TH was investigated by means of molecular modeling approaches. These data suggest that the amino acid residues, Glu429 and Ser354 of TH may play a pivotal role in the stabilization of CAPE within the active site as evaluated by molecular dynamics (MD) simulations. Gibbs binding free energy (ΔG_binding) of CAPE in complex with TH was also determined by post-processing MD analysis approaches (i.e. Poisson-Boltzmann Surface Area (MM-PBSA) method).