Chironomids and regional water types

The distribution pattern of 115 chironomid taxa at 664 sites, distributed over all kinds of water, was analyzed and related to 42 water types, based on the complete macrofauna composition. The distinction of chironomid groups was not useful to recognize water types. The use of individual chironomid taxa was more sensitive, though also too limited to recognize water types clearly. Chironomids are distributed along a continuum which is directed by master factors and detailed by habitat factors.     

Hydrophobic features of EPS extracted from anaerobic granular sludge: an investigation based on DAX-8 resin fractionation and size exclusion chromatography

The hydrophobic fractionation of extracellular polymeric substances (EPS) extracted from anaerobic granular sludge was performed on the DAX-8 resin (two elution pH conditions, i.e., pH 2 and pH 5 were tested). The impact of seven different EPS extraction methods on EPS hydrophobicity features was assessed. The results showed that the extraction methods and bulk solution pH influenced dramatically the biochemical composition of the EPS, and in turn, the hydrophobicity determined. Besides, EPS extracting reagents i.e., formaldehyde, ethanol, sodium dodecyl sulfate (SDS), and Tween 20 not only introduced extra carbon content in the total organic carbon (TOC) measurement but also interacted with the DAX-8 resin. By comparing the apparent molecular weight (aMW) distribution of untreated and pH-adjusted EPS samples, more complete EPS aMW information was preserved at pH 5. Thus, elution at pH 5 was preferred in this study for the qualitative analysis of EPS hydrophobic features. The hydrophobic fraction of EPS retained by the resin at pH 5 was ascribed to a wide aMW range, ranging from >440 to 0.3 kDa. Within this range, EPS molecules ranging from 175 to 31 kDa were mostly retained by the DAX-8 resin, which indicates that these EPS molecules are highly hydrophobic.

     

On the cost of vertical migration: are feeding conditions really worse at greater depths?

SUMMARY 1. The ultimate explanation for diel vertical migration (DVM) of zooplankton is the avoidance of visual predation in surface waters. Studies on migrating zooplankton have shown that remaining in the cold and food-poor hypolimnion during the day, however, has demographic costs. Higher temperatures and greater food concentrations in the surface waters are thought to be the main reasons why Daphnia species move upwards at night.
2. In this study, we investigated the growth condition of daphniids raised on seston taken from different depths from a lake with and without a deep-water chlorophyll maximum.
3. Juvenile growth rates of Daphnia galeata x hyalina from the lake without a deep-water chlorophyll maximum were similar for all treatments. After temperature correction, however, growth rates were significantly higher on seston taken from the surface layers.
4. In contrast, in the lake with the deep-water chlorophyll maximum, D. galeata growth rates were higher in deeper strata, even after temperature correction. Although this lake had a weak temperature gradient, D. galeata left the food-rich strata at night and migrated into the surface food-poor environment. Invertebrate predation and oxygen depletion are probably not the reasons for the nocturnal upward migration into the surface strata. Therefore, we assume that D. galeata migrates upwards to take advantage of higher temperatures. Using several temperature–egg-development models, we could not, however, fully explain this behaviour.     

Global in scope and regionally rich: an IndiSeas workshop helps shape the future of marine ecosystem indicators

This report summarizes the outcomes of an IndiSeas workshop aimed at using ecosystem indicators to evaluate the status of the world??s exploited marine ecosystems in support of an ecosystem approach to fisheries, and global policy drivers such as the 2020 targets of the Convention on Biological Diversity. Key issues covered relate to the selection and integration of multi-disciplinary indicators, including climate, biodiversity and human dimension indicators, and to the development of data- and model-based methods to test the performance of ecosystem indicators in providing support for fisheries management. To enhance the robustness of our cross-system comparison, unprecedented effort was put in gathering regional experts from developed and developing countries, working together on multi-institutional survey datasets, and using the most up-to-date ecosystem models.     

Parasite Fitness Traits Under Environmental Variation: Disentangling the Roles of a Chytrid’s Immediate Host and External Environment

Parasite environments are heterogeneous at different levels. The first level of variability is the host itself. The second level represents the external environment for the hosts, to which parasites may be exposed during part of their life cycle. Both levels are expected to affect parasite fitness traits. We disentangle the main and interaction effects of variation in the immediate host environment, here the diatom Asterionella formosa (variables host cell volume and host condition through herbicide pre-exposure) and variation in the external environment (variables host density and acute herbicide exposure) on three fitness traits (infection success, development time and reproductive output) of a chytrid parasite. Herbicide exposure only decreased infection success in a low host density environment. This result reinforces the hypothesis that chytrid zoospores use photosynthesis-dependent chemical cues to locate its host. At high host densities, chemotaxis becomes less relevant due to increasing chance contact rates between host and parasite, thereby following the mass-action principle in epidemiology. Theoretical support for this finding is provided by an agent-based simulation model. The immediate host environment (cell volume) substantially affected parasite reproductive output and also interacted with the external herbicide exposed environment. On the contrary, changes in the immediate host environment through herbicide pre-exposure did not increase infection success, though it had subtle effects on zoospore development time and reproductive output. This study shows that both immediate host and external environment as well as their interaction have significant effects on parasite fitness. Disentangling these effects improves our understanding of the processes underlying parasite spread and disease dynamics.     

Stimulation of the methyltetrahydromethanopterin: coenzyme M methyltransferase reaction in cell-free extracts of Methanobacterium thermoautotrophicum by the heterodisulfide of coenzyme M and 7-mercaptoheptanoylthreonine phosphate

The conversion of formaldehyde to methylcoenzyme M in cell-free extracts of Methanobacterium thermoautotrophicum was stimulated up to 10-fold by catalytic amounts of the heterodisulfide (CoM-S-S-HTP) of coenzyme M and 7-mercaptoheptanoylthreonine phosphate. The stimulation required the additional presence of ATP, also in catalytic concentrations. ATP and CoM-S-S-HTP were mutually stimulatory on the methylcoenzyme M formation and it was concluded that the compounds were both involved in the reductive activation of the methyltetrahydromethanopterin: coenzyme M methyltransferase. Micromolar concentrations of benzyl viologen or cyanocobalamin inhibited the formaldehyde conversion; these compounds, however, strongly stimulated the reduction of CoM-S-S-HTP. The results described here closely resemble observations made on the activation and reduction of CO₂ to formylmethanofuran indicating that this step and the reductive activation of the methyltransferase are controlled by some common mechanism.Abbreviations HS-CoM Coenzyme M, 2-mercaptoethanesulfonate - CH₃S-CoM methylcoenzyme M, 2-(methylthio)ethanesulfonate - H₄MPT 5,6,7,8-tetrahydromethanopterin - MFR methanofuran - HS-HTP 7-mercaptoheptanoylthreonine phosphate - CoM-S-S-HTP the heterodisulfide of HS-CoM and HS-HTP - BES 2-bromoethanesulfonate - TES N-tris(hydroxymethyl)methyl-2-aminoethanesulfonate - CN-Cbl cyanocobalamin - HO-Cbl hydroxycobalamin - HBI 5-hydroxybenzimidazole - DMBI 5,6-dimethylbenzimidazole     

Synthesis of 1,5-Anhydro-D-Mannitol Nucleosides with a Purine Base Moeety

Abstract

D-Mannitol nucleosides with a purine base moiety have been conveniently synthesized strating from 1,5-anhydro-4,6-O-benzylidene-D-glucitol. The 3-OH function of 1,5-anhydro-4,6-O-benzylidene-D-glucitol was selectively protected with t-butyldimethylsilyl group and subsequently converted to the corresponding 0-triflate derivative for the introduction of the nucleobase moietes. These nucleoside derivatives were transformed to 1,5-Anhydro-6-O-MMTr-2-(N⁶-benzoyladenin-9-yl)-2-deoxy-3-O-TBDMS-D-mannitol and 1,5-Anhydro-6-O-MMTr-2-(N²-isobutyryl-guanin-9-yl)-2-deoxy-3-O-TBDMS-D-mannitol, useful as the building blocks for oligonucleotide synthesis. Also, the synthesis of the corresponding fully deprotected anhydrohexitol nucleosides were achieved for evaluation of antiviral activity test.