Vicariance patterns in the Mediterranean Sea: east–west cleavage and low dispersal in the endemic seagrass Posidonia oceanica

Aim The seagrass, Posidonia oceanica is a clonal angiosperm endemic to the Mediterranean Sea. Previous studies have suggested that clonal growth is far greater than sexual recruitment and thus leads to low clonal diversity within meadows. However, recently developed microsatellite markers indicate that there are many different genotypes, and therefore many distinct clones present. The low resolution of markers used in the past limited our ability to estimate clonality and assess the individual level. New high‐resolution dinucleotide microsatellites now allow genetically distinct individuals to be identified, enabling more reliable estimation of population genetic parameters across the Mediterranean Basin. We investigated the biogeography and dispersal of P. oceanica at various spatial scales in order to assess the influence of different evolutionary factors shaping the distribution of genetic diversity in this species. Location The Mediterranean. Methods We used seven hypervariable microsatellite markers, in addition to the five previously existing markers, to describe the spatial distribution of genetic variability in 34 meadows spread throughout the Mediterranean, on the basis of an average of 35.6 (± 6.3) ramets sampled. Results At the scale of the Mediterranean Sea as a whole, a strong east–west cleavage was detected (amova) . These results are in line with those obtained using previous markers. The new results showed the presence of a putative secondary contact zone at the Siculo‐Tunisian Strait, which exhibited high allelic richness and shared alleles absent from the eastern and western basins. F statistics (pairwise θ ranges between 0.09 and 0.71) revealed high genetic structure between meadows, both at a small scale (about 2 to 200 km) and at a medium scale within the eastern and western basins, independent of geographical distance. At the intrameadow scale, significant spatial autocorrelation in six out of 15 locations revealed that dispersal can be restricted to the scale of a few metres. Main conclusions A stochastic pattern of effective migration due to low population size, turnover and seed survival is the most likely explanation for this pattern of highly restricted gene flow, despite the importance of an a priori seed dispersal potential. The east–west cleavage probably represents the outline of vicariance caused by the last Pleistocene ice age and maintained to this day by low gene flow. These results emphasize the diversity of evolutionary processes shaping the genetic structure at different spatial scales.     

Blood platelet surface interactions on fibrinogen under flow as viewed with fluorescent video-microscopy

The interaction of fluorescently labeled blood platelets with fibrinogen-coated glass was studied in Poiseuille flow at 3 wall shear rates, 40, 80 and 944 s-1. Observations were made via video-microscopy at a distance of 0.5 cm from a tube's entrance over a 1370 microns 2 portion of luminal area. The rates of arrival and detachment, and the net rate of adhesion of cells increased nonlinearly with flow rate. The fraction of arriving cells, first contacts, which adhered without subsequent movement and the fraction of arriving cells which adhered, moved to new positions and then remained adherent, were maximal at 80 s-1. For platelets which adhere and then move to a number of new positions, the likelihood of permanent adhesion is greater than 85 percent. The adhesion process is one in which 40-60 percent of cells permanently adhere on first contact with an additional 30 percent adhering after several moves along the surface. Cells contacting where a platelet was previously adherent had a greater chance of adhering than they would on an unaltered fibrinogen surface. The efficiency of platelet adhesion is greater for second contacts than for first contacts on unaltered fibrinogen coated surface.     

Identification of a prominent 85-kDa cAMP-dependent phosphoprotein associated with late G1 phase in mitogen-stimulated B lymphocytes

In order to elucidate late regulatory events which may be involved in the onset of S phase in B lymphocytes, we studied the effect of anti-Ig on phosphorylation of soluble proteins at late G1 phase. Stimulation of murine splenic B lymphocytes with anti-Ig and other mitogens for 18 h was found to be associated with a major increase in phosphorylation of an 85 kDa/pI approximately 5.3 cytosolic protein, conversely, stimulation of the cells with non-mitogenic stimuli did not induce the phosphorylation of pp85. The increase in phosphorylation of pp85 could not be detected after 30 min, was barely detectable after 6 h, but was very prominent after 18 h of stimulation with anti-Ig. Thus, the increase in phosphorylation of pp85 is not an early signal but is rather correlated with the late G1 phase. pp85 could not be detected in the nuclei of either control or stimulated cells. Stimulation of B cells for 30 min with forskolin induced the phosphorylation of pp85, while phorbol ester did not have any effect. The phosphorylation of pp85 was induced by the catalytic subunit of cAMP protein kinase. Comparison of the phosphopeptide map of pp85 phosphorylated by anti-Ig in intact cells to the phosphopeptide map phosphorylated by forskolin or by the catalytic subunit of cAMP protein kinase, showed a striking similarity indicating that cAMP protein kinase may be involved in phosphorylation of pp85 in mitogen-stimulated cells. An increase in intracellular cAMP levels at late G1 phase was found in B cells stimulated by mitogens. These results implicate an important role for cAMP-dependent phosphorylation events, specifically the phosphorylation of pp85/pI 5.3, at late G1 phase during the cell cycle.     

Identification of low frequency knockout mutants in Dictyostelium discoideum created by single or double homologous recombination

Generation and characterization of knockout clones is a widely used approach to evaluate the specific function of a gene product in Dictyostelium discoideum. The mutant clones are generally obtained by double homologous recombination in the target gene. A frequent limitation to obtaining mutants is the low frequency of homologous recombination. Here we present an easy method to identify rare mutants, based on PCR analysis of pools of clones. This method also allows the isolation of functional knockout mutants created by a single homologous recombination event, which can be more frequent than a double recombination event.     

Development of New Natural Extracts

For over the past 20 years, a remarkable development in the study and search of natural products has been observed. This is linked to a new market trend towards ecology and also due to new regulations. This could be a rupture, but also a real booster for creativity. Usually, in the flavor and fragrance field, creativity was boosted by the arrival of new synthetic molecules. Naturals remained the traditional, century‐old products, protected by secrecy and specific know‐how from each company. Regulatory restrictions or eco‐friendly certification constraints like hexane‐free processes triggered an important brainstorming in the industry. As a result, we developed new eco‐friendly processes including supercritical CO₂ extraction, allowing fresh plants to be used to obtain industrial flower extracts (Jasmine Grandiflorum, Jasmine Sambac, Orange blossom). These extracts are analyzed by GC, GC/MS, GC? O, and HPTLC techniques. New or unusual raw materials can also be explored, but the resulting extracts have to be tested for safety reasons. Some examples are described.     

Chemiluminescence of enterococci isolates from freshwater

All Enterococcus spp., isolated from environmental water samples (n=81), emitted a high chemiluminescence signal in the presence of luminol (10(-2) M). Kinetic studies of chemiluminescence show a close correlation between chemiluminescence and growth curves during the exponential phase, with a maximum chemiluminescence reached just before bacterial growth entered in the stationary phase. On the other hand, genera closely related to Enterococcus such as Streptococcus or Lactococcus produced a very weak chemiluminescent signal. Chemiluminescence of enterococci could therefore offer a rapid test, in aiding the identification of the genus Enterococcus and in the survey of the microbiological quality of water supplies.     

Borrelia burgdorferi binds fibronectin through a tandem beta-zipper, a common mechanism of fibronectin binding in staphylococci, streptococci, and spirochetes

BBK32 is a fibronectin-binding protein from the Lyme disease-causing spirochete Borrelia burgdorferi. In this study, we show that BBK32 shares sequence similarity with fibronectin module-binding motifs previously identified in proteins from Streptococcus pyogenes and Staphylococcus aureus. Nuclear magnetic resonance spectroscopy and isothermal titration calorimetry are used to confirm the binding sites of BBK32 peptides within the N-terminal domain of fibronectin and to measure the affinities of the interactions. Comparison of chemical shift perturbations in fibronectin F1 modules on binding of peptides from BBK32, FnBPA from S. aureus, and SfbI from S. pyogenes provides further evidence for a shared mechanism of binding. Despite the different locations of the bacterial attachment sites in BBK32 compared with SfbI from S. pyogenes and FnBPA from S. aureus, an antiparallel orientation is observed for binding of the N-terminal domain of fibronectin to each of the pathogens. Thus, these phylogenetically and morphologically distinct bacterial pathogens have similar mechanisms for binding to human fibronectin.     

Alpha repeat proteins (αRep) as expression and crystallization helpers

We have previously described a highly diverse library of artificial repeat proteins based on thermostable HEAT-like repeats, named αRep. αReps binding specifically to proteins difficult to crystallize have been selected and in several examples, they made possible the crystallization of these proteins. To further simplify the production and crystallization experiments we have explored the production of chimeric proteins corresponding to covalent association between the targets and their specific binders strengthened by a linker. Although chimeric proteins with expression partners are classically used to enhance expression, these fusions cannot usually be used for crystallization. With specific expression partners like a cognate αRep this is no longer true, and chimeric proteins can be expressed purified and crystallized. αRep selection by phage display suppose that at least a small amount of the target protein should be produced to be used as a bait for selection and this might, in some cases, be difficult. We have therefore transferred the αRep library in a new construction adapted to selection by protein complementation assay (PCA). This new procedure allows to select specific binders by direct interaction with the target in the cytoplasm of the bacteria and consequently does not require preliminary purification of target protein. αRep binders selected by PCA or by phage display can be used to enhance expression, stability, solubility and crystallogenesis of proteins that are otherwise difficult to express, purify and/or crystallize.