Characterization of Phospholipid Mixed Micelles by Translational Diffusion

The concentration dependence of the translational self diffusion rate, D (s), has been measured for a range of micelle and mixed micelle systems. Use of bipolar gradient pulse pairs in the longitudinal eddy current delay experiment minimizes NOE attenuation and is found critical for optimizing sensitivity of the translational diffusion measurement of macromolecules and aggregates. For low volume fractions Phi (Phi\\ le 15% v/v) of the micelles, experimental measurement of the concentration dependence, combined with use of the D (s)= D (o)(1-3.2lambdaPhi) relationship, yields the hydrodynamic volume. For proteins, the hydrodynamic volume, derived from D (s) at infinitely dilute concentration, is found to be about 2.6 times the unhydrated molecular volume. Using the data collected for hen egg white lysozyme as a reference, diffusion data for dihexanoyl phosphatidylcholine (DHPC) micelles indicate approximately 27 molecules per micelle, and a critical micelle concentration of 14 mM. Differences in translational diffusion rates for detergent and long chain phospholipids in mixed micelles are attributed to rapid exchange between free and micelle-bound detergent. This difference permits determination of the free detergent concentration, which, for a high detergent to long chain phospholipid molar ratio, is found to depend strongly on this ratio. The hydrodynamic volume of DHPC/POPC bicelles, loaded with an M2 channel peptide homolog, derived from translational diffusion, predicts a rotational correlation time that slightly exceeds the value obtained from peptide (15)N relaxation data.     

Increasing N deposition impacts neither diversity nor functions of deadwood‐inhabiting fungal communities,but adaptation and functional redundancy ensure ecosystem function

Nitrogen deposition can strongly affect biodiversity, but its specific effects on terrestrial microbial communities and their roles for ecosystem functions and processes are still unclear. Here, we investigated the impacts of N deposition on wood‐inhabiting fungi (WIF) and their related ecological functions and processes in a highly N‐limited deadwood habitat. Based on high‐throughput sequencing, enzymatic activity assay and measurements of wood decomposition rates, we show that N addition has no significant effect on the overall WIF community composition or on related ecosystem functions and processes in this habitat. Nevertheless, we detected several switches in presence/absence (gain/loss) of wood‐inhabiting fungal OTUs due to the effect of N addition. The responses of WIF differed from previous studies carried out with fungi living in soil and leaf‐litter, which represent less N‐limited fungal habitats. Our results suggest that adaptation at different levels of organization and functional redundancy may explain this buffered response and the resistant microbial‐mediated ecosystem function and processes against N deposition in highly N‐limited habitats.     

Beta blockers after myocardial infarction: have trials changed practice?

A survey of British consultant cardiologists was carried out to elicit their current practices when prescribing long term beta blockers after myocardial infarction. Sixty (72%) of the respondents reported that they used beta blockers prophylactically even in the absence of any other indications; the details of their stated policies, however, varied considerably. The favourable evidence of clinical trials in this indication appears to have been assimilated into hospital practice.     

The relationship between wetland hydroperiod and nestedness patterns in assemblages of larval amphibians and predatory macroinvertebrates

Assemblages exhibit nested distributional patterns if the species found in species-poor locations also occur in progressively richer locations. We investigated patterns of nestedness in assemblages of larval amphibians and predatory macroinvertebrates in 42 isolated freshwater wetlands in southern New Hampshire, USA. These wetlands varied markedly in hydroperiod and we predicted that nestedness would be relatively weak because changes in disturbance processes (the relative threat of desiccation and predation) along the hydroperiod gradient often generate distinct assemblages. Contrary to expectations we found that both amphibian and macroinvertebrate assemblages were strongly nested not only with respect to species richness but also with respect to hydroperiod and wetland size, which were positively correlated. We attribute our results to the increased colonization rates and decreased extinction rates associated with increasing hydroperiod, and to concomitant increases in wetland size, habitat heterogeneity/complexity, and possibly water temperature. Moreover, the impact of predatory fishes on species richness and composition of amphibians and macroinvertebrates was relatively minor. We found that amphibians had a significantly lower degree of nestedness than macroinvertebrates, suggesting that a higher proportion of amphibian species found in species-poor assemblages was unlikely to occur in species-rich assemblages of amphibians (e.g. wood frogs and spotted salamanders). The degree of nestedness appeared to be influenced primarily by hydroperiod and wetland size for amphibians, whereas nestedness of macroinvertebrates was influenced by unknown factors (possibly water temperature) in addition to hydroperiod and wetland size. The high degrees of nestedness observed in amphibian and macroinvertebrate assemblages imply that protection of larger, more permanent wetlands may be more important for conserving native biological diversity than protection of smaller, non-permanent wetlands. However, non-permanent wetlands are used by several species of conservation concern that often do not occur in larger and more permanent wetlands.     

Seasonal climate effects anemotaxis in newly emerged adult Anopheles gambiae Giles in Mali, West Africa

The direction and magnitude of movement by the malaria vector Anopheles gambiae Giles has been of great interest to medical entomologists for over 70 years. This direction of movement is likely to be affected by many factors, from environmental conditions and stage of life history of the mosquito to the existence of attractants in the vicinity. We report here the direction of movement of newly emerged An. gambiae in nature, around the village of Donéguébougou, Mali. We assessed the direction of movement for individual mosquitoes by placing them in a novel enclosure with exit traps oriented in the direction of the cardinal and intermediate points of the compass. We consistently found predominantly Southward directions of movement during 2009 and 2010, with an additional Eastward component during the dry season and a Westward one during the wet season. Our data indicate that wind has an important effect on the direction of movement, but that this effect varied by season: Average directions of movement were downwind during the dry season and upwind during the wet season. A switch in anemotactic response suggests that the direction of movement of An. gambiae relative to the wind immediately after emergence under varying conditions of humidity should be further investigated under controlled conditions.     

Macroinvertebrate community structure across a wetland hydroperiod gradient in southern New Hampshire,USA

We conducted a field study to examine the influence of hydroperiod and concomitant changes in abiotic (wetland size, pH, conductivity, dissolved oxygen and water temperature) and biotic (predatory fish presence) characteristics on macroinvertebrate communities in isolated wetlands in southern New Hampshire. Invertebrates were sampled using dipnet sweeps in 42 wetlands with short (<4 months), intermediate (4–11 months) or long (permanent) hydroperiods in 1998 and 1999. We found that invertebrate genera richness, and to a lesser degree abundance, increased linearly along the hydrological gradient, and in response to temperature and dissolved oxygen. Relative abundance of genera also differed markedly with respect to hydroperiod. Most notably, invertebrate communities changed from Acilius-dominated communities to Notonecta-dominated communities. Invertebrate relative abundances in permanent wetlands also differed with respect to the occurrence of predatory fish. Some genera (e.g., Libellula, and Dytiscus) were more likely to occur in permanent wetlands without fish, whereas other genera (e.g., Buena, and Basiaeshna) were more likely to occur in wetlands with predatory fish. Because aquatic invertebrate communities differed markedly with respect to wetland hydroperiod, and in relation to the occurrence of predatory fish, it is essential to retain a diversity of wetlands in the landscape to ensure the long-term persistence of aquatic invertebrate biodiversity.