Stable isotope fractionation of strontium in coccolithophore calcite: Influence of temperature and carbonate chemistry

Marine calcifying eukaryotic phytoplankton (coccolithophores) is a major contributor to the pelagic production of CaCO₃ and plays an important role in the biogeochemical cycles of C, Ca and other divalent cations present in the crystal structure of calcite. The geochemical signature of coccolithophore calcite is used as palaeoproxy to reconstruct past environmental conditions and to understand the underlying physiological mechanisms (vital effects) and precipitation kinetics. Here, we present the stable Sr isotope fractionation between seawater and calcite (Δ^88/86Sr) of laboratory cultured coccolithophores in individual dependence of temperature and seawater carbonate chemistry. Coccolithophores were cultured within a temperature and a pCO₂ range from 10 to 25°C and from 175 to 1,240 μatm, respectively. Both environmental drivers induced a significant linear increase in coccolith stable Sr isotope fractionation. The temperature correlation at constant pCO₂ for Emiliania huxleyi and Coccolithus braarudii is expressed as Δ^88/86Sr = ?7.611 × 10^?3 T + 0.0061. The relation of Δ^88/86Sr to pCO₂ was tested in Emiliania huxleyi at 10 and 20°C and resulted in Δ^88/86Sr = ?5.394 × 10^?5 pCO₂ – 0.0920 and Δ^88/86Sr = ?5.742 × 10^?5 pCO₂ – 0.1351, respectively. No consistent relationship was found between coccolith Δ^88/86Sr and cellular physiology impeding a direct application of fossil coccolith Δ^88/86Sr as coccolithophore productivity proxy. An overall significant correlation was detected between the elemental distribution coefficient (D_Sr) and Δ^88/86Sr similar to inorganic calcite with a physiologically induced offset. Our observations indicate (i) that temperature and pCO₂ induce specific effects on coccolith Δ^88/86Sr values and (ii) that strontium elemental ratios and stable isotope fractionation are mainly controlled by precipitation kinetics when embedded into the crystal lattice and subject to vital effects during the transmembrane transport from seawater to the site of calcification. These results provide an important step to develop a coccolith Δ^88/86Sr palaeoproxy complementing the existing toolbox of palaeoceanography.     

Integrating ARC grid middleware with Taverna workflows

Summary: This work presents two independent approaches for aseamless integration of computational grids with the bioinformaticsworkflow suite Taverna. These are supported by a unique relationaldatabase to link applications with grid resources and presentsthose as workflow elements. A web portal facilitates its collaborativemaintenance. The first approach implements a gateway serviceto handle authentication certificates and all communicationwith the grid. It reads the database to spawn web services forworkflow elements which are in turn used by Taverna. The secondapproach lets Taverna communicate with the grid on its own,by means of a newly developed plug-in. It reads the databaseand executes the needed tasks directly on the grid. While thegateway service is non-intrusive, the plug-in has technicaladvantages, e.g. by allowing data to remain on the grid whilebeing passed between workflow elements. Availability: http://grid.inb.uni-luebeck.de/ Contact: bayer{at}inb.uni-luebeck.de Associate Editor: Alfonso Valencia     

Differences in growth,size and sexual dimorphism in skulls of East Greenland and Svalbard polar bears (<Emphasis Type="Italic">Ursus maritimus</Emphasis>)

Size, growth and sexual dimorphism of nine skull traits was studied in 300 East Greenland and 391 Svalbard polar bears (Ursus maritimus). Two traits were significantly larger in bears from East Greenland compared to Svalbard bears, and trait size was smaller after 1960 in five traits. For both localities and both age groups (subadult, adult), mean trait size values were higher in males than females (all: P < 0.05). Gompertz growth models showed trait size increasing with age in seven traits. Depending on the trait, males reached 95% asymptotic trait size at age 3–10, females at age 2–6. The females of both localities matured at approximately the same age, whereas the Svalbard males generally matured years later than their East Greenland peers. The differences found in the present study between the two polar bear subpopulations support the notion that East Greenland and Svalbard polar bears probably should be managed as separate units.     

Vegetation indicators for grazing activities on grassland to be implemented in outcome-oriented agri-environmental payment schemes in North-East Germany

In this study a new field of action for outcome-oriented payment schemes (payments by results) is introduced. That is the promotion of extensive summer grazing activities of livestock. Combining this objective with methods of outcome-oriented rewarding means to tie the payment to vegetation criteria indicating regular grazing activities instead of regularly controlling the presence of livestock on the field. In comparison to action-oriented concepts, the main advantage of this approach is that only one inspection walk is required. The paper describes and evaluates the first attempt to determine suitable indicator species for such a scheme. We pre-tested the approach with existing vegetation data only. A database of relevés, plant species and agriculturally used grassland communities of the regional district Doberan, Mecklenburg-Western Pomerania (Germany) was utilised. Grazing activities can be identified by the existence of a specific number of vascular species indicating grazing activities on a particular grassland field. We utilised the indicator function of grassland communities for management conditions to resolve the deficiency of data base relevés for providing no data about the management regime. The pasture community Lolio perennis-Cynosuretum cristati was used as a reference system to pre-test the suitability of different combinations of potential indicator species for separating pasture from non-pasture grassland. A tentative quantitative selection criterion for pasture grassland was proposed. That is the number of indicator species a relevé/grassland field has to hold to be identified as pasture grassland. Database relevés are not sufficient for calibrating such a concept, though. It is necessary to adjust the indicator species list to other drivers like use characteristics, nutrient availability, and soil moisture level. Here additional fieldwork is needed. As a first evidence for the validity of the concept, the suitability of the indicator list was measured by testing the correct identification of pasture grassland in a long-term grassland experiment built by the treatments “grazing” and “mowing”. ANOVA tests on the precision of the indicator species showed significant results. In the discussion a modification of the inventory method of grassland fields was recommended. The precision of the developed concept could be further enhanced by introducing the species dominance as a second factor deciding about the correct identification of pasture use.     

Quorum quenching is an antivirulence strategy employed by endophytic bacteria

Bacteria predominantly use quorum sensing to regulate a plethora of physiological activities such as cell-cell crosstalk, mutualism, virulence, competence, biofilm formation, and antibiotic resistance. In this study, we investigated how certain potent endophytic bacteria harbored in Cannabis sativa L. plants use quorum quenching as an antivirulence strategy to disrupt the cell-to-cell quorum sensing signals in the biosensor strain, Chromobacterium violaceum. We used a combination of high-performance liquid chromatography high-resolution mass spectrometry (HPLC-ESI-HRMSⁿ) and matrix-assisted laser desorption ionization imaging high-resolution mass spectrometry (MALDI-imaging-HRMS) to first quantify and visualize the spatial distribution of the quorum sensing molecules in the biosensor strain, C. violaceum. We then showed, both quantitatively and visually in high spatial resolution, how selected endophytic bacteria of C. sativa can selectively and differentially quench the quorum sensing molecules of C. violaceum. This study provides fundamental insights into the antivirulence strategies used by endophytes in order to survive in their ecological niches. Such defense mechanisms are evolved in order to thwart the plethora of pathogens invading associated host plants in a manner that prevents the pathogens from developing resistance against the plant/endophyte bioactive secondary metabolites. This work also provides evidence towards utilizing endophytes as tools for biological control of bacterial phytopathogens. In continuation, such insights would even afford new concepts and strategies in the future for combating drug resistant bacteria by quorum-inhibiting clinical therapies.     

Load transfer along the bone–dental implant interface

In this paper the variation of normal and shear stresses along a path defined on the bone–dental implant interface is investigated. In particular, the effects of implant diameter, collar length and slope, body length, and the effects of four different types of external threads on the interfacial stress distribution are studied. The geometry of the bone is digitized from a CT scan of a mandibular incisor and the surrounding bone. The bone and the implant are assumed to be perfectly bonded. The finite element method with 2D plane strain assumption is used to compute interfacial stresses. Highest continuous interfacial stresses are encountered in the region where the implant collar engages the cortical region, and near the apex of the implant in the subcortical region. Stress concentrations in the interfacial stresses occur near the geometric discontinuities on the implant contour, and jumps in stress values occur where the elastic modulus of the bone transitions between the cortical and trabecular bone values. Among the six contour parameters, the slope and the length of the implant collar, and the implant diameter influence the interfacial stress levels the most, and the effects of changing these parameters are significantly noticed only in the cortical bone (alveolar ridge) area. External threads cause significant stress concentrations in interfacial stresses in otherwise smoothly varying regions. This work shows that the presence of external threads could cause significant variations in both normal and shear stresses along the bone–implant interface, but not reduction in shear stress as previously thought.     

Cloning and molecular characterization of the HgiCI restriction/modification system from Herpetosiphon giganteus Hpg9 reveals high similarity to BanI.

The genes coding for the GGYRCC specific restriction/modification system HgiCI from Herpetosiphon giganteus Hpg9 have been cloned in Escherichia coli in three steps. As an initial step, the methyltransferase gene could be obtained after heterologous in vitro selection of a plasmid gene bank by cleavage with the isoschizomeric restriction endonuclease BanI. The adjacent endonuclease gene was cloned following Southern blot analysis of flanking genomic regions. The two genes code for polypeptides of 420 amino acids (M.HgiCI) and 345 amino acids (R.HgiCI). Establishing a functional endonuclease gene could only be achieved using a tightly regulated expression system or by methylation of the genomic DNA prior to transformation of the endonuclease gene. The methyltransferase M.HgiCI shows significant similarities to the family of 5-methylcytidine methyltransferases. Striking similarities could be found with both the isoschizomeric endonuclease and methyltransferase of the BanI restriction/modification system from Bacillus aneurinolyticus.     

Stepwise cloning and molecular characterization of the HgiDI restriction-modification system from Herpetosiphon giganteus Hpa2.

The restriction-modification system HgiDI from Herpetosiphon giganteus strain Hpa2 has been cloned in E. coli in a two-step procedure. Selection of the methyltransferase (M.HgiDI) gene in vitro was performed using the heterologous restriction endonuclease AhaII, an isoschizomer of Acyl and HgiDI (GRCGYC). Cloning of the complete HgiDI endonuclease (R.HgiDI) gene could only be achieved in recipient cells harbouring a recombinant plasmid, which was expressing the corresponding methyltransferase and could thereby prevent the host from self-destruction of its genetic material. The HgiDI restriction-modification system was sequenced and functionally correlated with two open reading frames of 309 (M) and 359 (R) codons. In homology studies M.HgiDI showed significant similarities to 20 other m5C-methyltransferases and turned out to be the most compact enzyme of this group described so far. Initial attempts for overexpression of M.HgiDI and partial purification of R.HgiDI have been successful.