Arthropod phylogeny: An overview from the perspectives of morphology,molecular data and the fossil record

Monophyly of Arthropoda is emphatically supported from both morphological and molecular perspectives. Recent work finds Onychophora rather than Tardigrada to be the closest relatives of arthropods. The status of tardigrades as panarthropods (rather than cycloneuralians) is contentious from the perspective of phylogenomic data. A grade of Cambrian taxa in the arthropod stem group includes gilled lobopodians, dinocaridids (e.g., anomalocaridids), fuxianhuiids and canadaspidids that inform on character acquisition between Onychophora and the arthropod crown group. A sister group relationship between Crustacea (itself likely paraphyletic) and Hexapoda is retrieved by diverse kinds of molecular data and is well supported by neuroanatomy. This clade, Tetraconata, can be dated to the early Cambrian by crown group-type mandibles. The rival Atelocerata hypothesis (Myriapoda + Hexapoda) has no molecular support. The basal node in the arthropod crown group is embroiled in a controversy over whether myriapods unite with chelicerates (Paradoxopoda or Myriochelata) or with crustaceans and hexapods (Mandibulata). Both groups find some molecular and morphological support, though Mandibulata is presently the stronger morphological hypothesis. Either hypothesis forces an unsampled ghost lineage for Myriapoda from the Cambrian to the mid Silurian.     

Bioengineering and characterization of DNA-protein assemblies floating on supported membranes.

A biodevice involving thiolated ssDNA and engineered cytochrome b5 linked through a cis-platine bridge is described. This original nanostructure is associated to a supported membrane through a floating anchor, thus constituting a dynamic bidimensionnal DNA capture device contrasting with the constrained geometry of currently available DNA chips. Characterization by optical spectroscopy, surface plasmon resonance and gel electrophoresis demonstrated that an unique molecular supra-assembly featuring specific DNA recognition capability has been obtained. This device is characterized by the reversibility of its assembly, self-organization and fluidity properties and is of interest as a prototype to design new generations of DNA chip biosensors.     

Diauxic growth of Clostridium thermosaccharolyticum on glucose and xylose

Abstract Clostridium thermosaccharolyticum growing on medium containing glucose and xylose exhibits classical diauxic growth in which glucose is utilized during the first phase. The lag period between growth phases is associated with induction of synthesis of a xylose transport system together with the enzymes xylose isomerase and xylukokinase. Xylose metabolism by this organism is therefore shown to be inducible and subject to repression by glucose. Xylose utilization by cells adapted to this carbon source is also prevented immediately upon addition of glucose to the culture, suggesting a direct inhibitory effect of glucose on xylose uptake or metabolism.