New Insights into the Diversity of Marine Picoeukaryotes

Over the last decade, culture-independent surveys of marine picoeukaryotic diversity based on 18S ribosomal DNA clone libraries have unveiled numerous sequences of novel high-rank taxa. This newfound diversity has significantly altered our understanding of marine microbial food webs and the evolution of eukaryotes. However, the current picture of marine eukaryotic biodiversity may be significantly skewed by PCR amplification biases, occurrence of rDNA genes in multiple copies within a single cell, and the capacity of DNA to persist as extracellular material. In this study we performed an analysis of the metagenomic dataset from the Global Ocean Survey (GOS) expedition, seeking eukaryotic ribosomal signatures. This PCR-free approach revealed similar phylogenetic patterns to clone library surveys, suggesting that PCR steps do not impose major biases in the exploration of environmental DNA. The different cell size fractions within the GOS dataset, however, displayed a distinct picture. High protistan diversity in the <0.8 µm size fraction, in particular sequences from radiolarians and ciliates (and their absence in the 0.8–3 µm fraction), suggest that most of the DNA in this fraction comes from extracellular material from larger cells. In addition, we compared the phylogenetic patterns from rDNA and reverse transcribed rRNA 18S clone libraries from the same sample harvested in the Mediterranean Sea. The libraries revealed major differences, with taxa such as pelagophytes or picobiliphytes only detected in the 18S rRNA library. MAST (Marine Stramenopiles) appeared as potentially prominent grazers and we observed a significant decrease in the contribution of alveolate and radiolarian sequences, which overwhelmingly dominated rDNA libraries. The rRNA approach appears to be less affected by taxon-specific rDNA copy number and likely better depicts the biogeochemical significance of marine protists

Rice straw as an alternative reinforcement in polypropylene composites

We studied the use of rice straw as reinforcement in maleated polypropylene (PPm). Composites containing 20 and 30% by weight rice straw were successfully prepared by extrusion and compression molding. The samples were characterized by tensile tests, differential scanning calorimetry (DSC), thermogravimetry (TGA), dynamo-mechanical analysis (DMTA) and scanning electron microscopy (SEM). The results of the mechanical properties showed that rice straw can be used as an alternative reinforcement for polypropylene. Higher tensile moduli (E) were obtained for composites containing higher rice straw content. Thermogravimetric curves of the composites exhibit two-stage decomposition process and slightly higher thermal stability. Higher crystallization (Tc) and melting peak temperatures for composites were detected by DSC analysis (Tcpp = 107.8 °C, TcRS/PP(20/80) = 114.5 °C). The renewability of rice straw and the recyclability of thermoplastic polypropylene provide an attractive eco-friendly quality to the resulting composites

Search for the neutral MSSM Higgs bosons in the b b H, H \to \mu^+ \mu^- topology

Contains fulltext : 72602.pdf (publisher's version ) (Closed access)ICHEP 2007, 19 juli 200