The gall miteAceria cladophthirus. I. Life-cycle,survival outside the gall and symptoms' expression on susceptible or resistantSolanum dulcamara plants

The gall miteAceria cladophthirus (Nalepa) is able to survice outside its gall on detached leaves ofSolanum dulcamara L. kept under non-aseptic in-vitro conditions. The survival rate of the females on susceptible leaves is about 90% after 1 day and 85% for the following days. In contrast, on resistant leaves, less than 40$ survive after 1 day while necrotic local lesions develop and later the mortality increases severely. However, the mite only completes its life-cycle on susceptible leaves. The life-cycle forA. cladophthirus takes about 12 days: six days for egg incubation and six days for two instars growth. Its life-history is simple, without alternating females specialised for hibernation; arrhenotokous parthenogenesis occurs in experimental conditions. Eggs do not play any role in gall formation. Immature stages induce gall symptoms but are less efficient than females. Mite feeding only induces complete gall symptoms on the less differentiated leaves of susceptible shoots. On susceptible detached leaves, gall symptoms are similar but weaker and their intensity decreases with increasing leaf age; fully expanded leaves remain free of symptoms.On resistant plants, mite feeding induces a hypersensitive response: necrotic local lesions, about 350 m in diameter, appear both on shoots and on detached leaves. However, young leaves develop smaller lesions than old ones. Females induce larger lesions than first larvae. Once necrosis formation is initiated, it proceeds to completion regardless of the duration of mite feeding.     

Transmission of molecularly undetectable circulating parasite clones leads to high infection complexity in mosquitoes post feeding

Plasmodium falciparum malaria infections often comprise multiple distinct parasite clones. Few datasets have directly assessed infection complexity in humans and mosquitoes they infect. Examining parasites using molecular tools may provide insights into the selective transmissibility of isolates. Using capillary electrophoresis genotyping and next generation amplicon sequencing, we analysed complexity of parasite infections in human blood and in the midguts of mosquitoes that became infected in membrane feeding experiments using the same blood material in two West African settings. Median numbers of clones in humans and mosquitoes were higher in samples from Burkina Faso (4.5, interquartile range 2–8 for humans; and 2, interquartile range 1–3 for mosquitoes) than in The Gambia (2, interquartile range 1–3 and 1, interquartile range 1–3, for humans and mosquitoes, respectively). Whilst the median number of clones was commonly higher in human blood samples, not all transmitted alleles were detectable in the human peripheral blood. In both study sample sets, additional parasite alleles were identified in mosquitoes compared with the matched human samples (10–88.9% of all clones/feeding assay, n?=?73 feeding assays). The results are likely due to preferential amplification of the most abundant clones in peripheral blood but confirm the presence of low density clones that produce transmissible sexual stage parasites.     

A near death experience: Shigella manipulates host death machinery to silence innate immunity

Release of mitochondrial contents often triggers inflammation and cell death, and modulating this process can be advantageous to invading pathogens. In this issue of The EMBO Journal, Andree and colleagues reveal new findings that an intracellular bacterial pathogen exploits apoptotic machinery to suppress host immune signaling, yet avoids cell death. This study emphasizes the need to expand our understanding of the roles played by pro‐apoptotic proteins in non‐death scenarios.     

A career at the interface of cell and developmental biology: a view from the crest

Just as neural crest cells migrate great distances through the embryo, my journey has taken me from a childhood in a distant land to a career as a biologist. My mentoring relationships have shaped not only the careers of my trainees, but also the trajectory of my own science. One of the most satisfying aspects of mentoring comes from helping to empower the next generation of scientists to do more tomorrow than is possible today. This, together with a passion for discovery and learning new things, motivates me and makes science such a rewarding career.First, let me say how honored I am to receive the Women in Cell Biology Senior Award. I am particularly thankful to my former postdoctoral fellows and students. I have learned as much, or more, from them as they have from me and take great pride and vicarious pleasure from their successes. My goal as a mentor has been to impart an enthusiasm for science and for the satisfaction it can bring at both a professional and personal level. It is the pleasure of discovery and the bonds of collegiality that make being a scientist not only a worthwhile and interesting but also a very fulfilling career.When looking back upon my life as a biologist, many of the “choices” made along my career path were more of a random walk than a premeditated trajectory. Perhaps the most important and constant influences come from my family background, wonderful friends and colleagues, and an inherent interest in the natural world. For me, these were mixed with a good deal of luck and the generous mentorship of valued colleagues.     

Role of Rfe and RfbF in the initiation of biosynthesis of D-galactan I, the lipopolysaccharide O antigen from Klebsiella pneumoniae serotype O1.

The 6.6-kb rfb gene cluster from Klebsiella pneumoniae serotype O1 (rfbKpO1) contains six genes whose products are required for the biosynthesis of a lipopolysaccharide O antigen with the following repeating unit structure: -->3-beta-D-Galf-1-->3-alpha-D-Galp-1-->(D-galactan I). rfbFKpO1 is the last gene in the cluster, and its gene product is required for the initiation of D-galactan I synthesis. Escherichia coli K-12 strains expressing the RfbFKpO1 polypeptide contain dual galactopyranosyl and galactofuranosyl transferase activity. This activity modifies the host lipopolysaccharide core by adding the disaccharide beta-D-Galf-1-->3-alpha-D-Galp, representing a single repeating unit of D-galactan I. The formation of the lipopolysaccharide substituted either with the disaccharide or with authentic polymeric D-galactan I is dependent on the activity of the Rfe enzyme. Rfe (UDP-GlcpNAc::undecaprenylphosphate GlcpNAc-1-phosphate transferase) catalyzes the formation of the lipid-linked biosynthetic intermediate to which galactosyl residues are transferred during the initial steps of D-galactan I synthesis. The rfbFKpO1 gene comprises 1,131 nucleotides, and the predicted polypeptide consists of 373 amino acid residues with a predicted M(r) of 42,600. A polypeptide with an M(r) of 42,000 was evident in sodium dodecyl sulfate-polyacrylamide gels when rfbKpO1 was expressed behind the T7 promoter. The carboxy-terminal region of RfbFKpO1 shares similarity with the carboxy terminus of RfpB, a galactopyranosyl transferase which is involved in the synthesis of the type 1 O antigen of Shigella dysenteriae.     

Metagenomic approach studying the taxonomic and functional diversity of the bacterial community in a mesotrophic lake (Lac du Bourget – France)

The main goals of this work were to identify the metabolic pathways of the bacterial community in a lacustrine ecosystem and to establish links between taxonomic composition and the relative abundances of these metabolic pathways. For this purpose, we analysed a 16S rRNA gene library obtained by gene amplification together with a sequence library of both insert ends on c . 7700 fosmids. Whatever the library used, Actinobacteria was the most abundant bacterial group, followed by Proteobacteria and Bacteroidetes . Specific aquatic clades such as acI and acIV ( Actinobacteria ) or LD12 and GOBB-C201 ( Alphaproteobacteria ) were found in both libraries. From comparative analysis of metagenomic libraries, the metagenome of this lake was characterized by overrepresentation of genes involved in the degradation of xenobiotics mainly associated with Alphaproteobacteria . Actinobacteria were mainly related to metabolic pathways involved in nucleotide metabolism, cofactors, vitamins, energy, replication and repair. Betaproteobacteria appeared to be characterized by the presence of numerous genes implicated in environmental information processing (membrane transport and signal transduction) whereas glycan and carbohydrate metabolism pathways were overrepresented in Bacteroidetes . These results prompted us to propose hypotheses on the ecological role of these bacterial classes in lacustrine ecosystems.     

Rapid double 8-nm steps by a kinesin mutant

The mechanism by which conventional kinesin walks along microtubules is poorly understood, but may involve alternate binding to the microtubule and hydrolysis of ATP by the two heads. Here we report a single amino-acid change that affects stepping by the motor. Under low force or low ATP concentration, the motor moves by successive 8-nm steps in single-motor laser-trap assays, indicating that the mutation does not alter the basic mechanism of kinesin walking. Remarkably, under high force, the mutant motor takes successive 16-nm displacements that can be resolved into rapid double 8-nm steps with a short dwell between steps, followed by a longer dwell. The alternating short and long dwells under high force demonstrate that the motor stepping mechanism is inherently asymmetric, revealing an asymmetric phase in the kinesin walking cycle. Our findings support an asymmetric two-headed walking model for kinesin, with cooperative interactions between the two heads. The sensitivity of the 16-nm displacements to nucleotide and load raises the possibility that ADP release is a force-producing event of the kinesin cycle.