Cannibalism and Interspecific Predation in a Phytoseiid Predator Guild from Cassava Fields in Africa: Evidence from the Laboratory

Interspecific predation and cannibalism are common types of interaction in phytoseiid predator guilds, but the extent and nature of these interactions have not been determined yet in phytoseiid guilds composed of African native and neotropical exotic phytoseiid predators found in cassava habitat in southern Africa. We determined in laboratory experiments the level of cannibalism and interspecific predation among the three phytoseiid mite species Euseius fustis, Iphiseius degenerans, and Typhlodromalus aripo in the absence of food and in the presence of limited or abundant quantities of two food types – Mononychellus tanajoa and maize pollen – commonly found on cassava in Africa. When confined without food, only two T. aripo females laid each two eggs within 5 days, and this species survived longer than I. degenerans and E. fustis. In the presence of con- or hetero-specific larvae or protonymphs, the three species fed more on the former than on the latter, and more on hetero-specifics than on con-specifics. Oviposition rates of the three species did not exceed 0.7 egg/female/day on con- and hetero-specific immatures. Typhlodromalus aripo and E. fustis survived longer on con-specific and hetero-specific larvae and on hetero-specific protonymphs than in the absence of any food, while T. aripo survived longer than the two other species on the same diets. Provision of limited quantity of food decreased interspecific predation rate by I. degenerans and T. aripo, but not by E. fustis, and increased oviposition rate and longevity of all three species. Provision of abundant food, however, eliminated cannibalism by all three species and further reduced interspecific predation rates, but their oviposition and longevity remained relatively unchanged compared with limited food provision. Potential consequences of cannibalism and interspecific predation among phytoseiid mites on cassava for the biological control of M. tanajoa are discussed.     

Entamoeba histolytica: inhibition of cellular functions by overexpression of EhGEF1, a novel Rho/Rac guanine nucleotide exchange factor

The molecular, biochemical, and cellular characterization of EhGEF1 protein is described. Complete cDNA sequence of 1890 bp revealed an open reading frame that encodes a protein of 69 kDa. EhGEF1 is constituted of Dbl homology domain, pleckstrin homology domain, and several putative regulation sites. Studies of guanine nucleotide exchange activity of EhGEF1 on several GTPases from Entamoeba histolytica and Homo sapiens showed preferential activation on EhRacG, suggesting that EhGEF1 protein could be involved in mechanisms related to actin cytoskeleton activation, cytokinesis, capping, and uroid formation in trophozoite. Confocal microscopy studies of pExEhNeo/HSV-tagged-EhGEF1-transfected cells showed that trophozoites stimulated with ConA, EhGEF1, and EhRacG were localized at plasma membrane. Cellular studies showed that F-actin content of pExEhNeo/HSV-tagged-EhGEF1-transfected trophozoites as well as cellular migration and cell damage capacity were significantly altered. The observations suggest that EhRacG was the principal target of EhGEF1 and that EhGEF1 may provide a link between F-actin dynamics and EhRacG signaling.     

Comparison of growth and condition indices of juvenile flatfish in differentcoastal nursery grounds

Coastal and estuarine ecosystems in the eastern channel and southern bight of the North Sea provide nursery habitats for juvenile fishes. We examined the age 0-group juveniles of three flatfish speciesSolea solea, Limanda limanda and Pleuronectes platessa, collected in five nursery areas with different characteristics (three sites located near small estuaries and two affected by important inputs of industrial effluents), to evaluate habitat influence on their growth and condition. We measured a biochemical index (RNA:DNA ratio), a morphometric index (Fultons K condition index), plus a recent growth index (marginal otolith increment width) on each individual (about 3months old), collected during surveys in autumn 1999. The three indices displayed few significant differences among the five nursery sites and different patterns for each species. We suggest that the investigated nursery areas provide habitats of equivalent quality for the age 0-group juvenile flatfishes in spite of different anthropogenic disturbances. On the other hand, this study focuses on the importance of using different biological indicators to assess habitat quality and environmental stressors in coastal areas.     

Compartmentalization of hepatitis C virus genotypes between plasma and peripheral blood mononuclear cells

Differences in hepatitis C virus (HCV) variants of the highly conserved 5' untranslated region (UTR) have been observed between plasma and peripheral blood mononuclear cells (PBMC). The prevalence and the mechanisms of this compartmentalization are unknown. Plasma and PBMC HCV variants were compared by single-strand conformation polymorphism (SSCP) and by cloning or by genotyping with a line probe assay (LiPA) in 116 chronically infected patients, including 44 liver transplant recipients. SSCP patterns differed between compartments in 43/109 analyzable patients (39%). Differences were significantly more frequent in patients with transplants (21/38 [55%] versus 22/71 [31%]; P < 0.01) and in those who acquired HCV through multiple transfusions before 1991 (15/20; 75%) or through drug injection (16/31; 52%) than in those infected through an unknown route (7/29; 24%) or through a single transfusion (5/29; 17%; P < 0.001). Cloning of the 5' UTR, LiPA analysis, and nonstructural region 5B sequencing revealed different genotypes in the two compartments from 10 patients (9%). In nine patients, the genotype detected in PBMC was not detected in plasma and was weak or undetectable in the liver in three cases. This genotypic compartmentalization persisted for years in three patients and after liver transplantation in two. The present study shows that a significant proportion of HCV-infected subjects harbor in their PBMC highly divergent variants which were likely acquired through superinfections.     

Synthesis of half-mustard combi-molecules with fluorescence properties: correlation with EGFR status

The synthesis of 6-(2-chloroethylamino)-4-anilinoquinazolines ZR2002 and ZR2003 designed to block EGFR tyrosine kinase and to damage genomic DNA is described. These compounds present fluorescence properties that permitted the quantitation of their subcellular uptake by flow cytometry. Fluorescence intensities increased with increasing levels of EGFR in a panel of isogenic and established cell lines.     

Challenges in Developing Electrodes,Electrolytes, and Diagnostics Tools to Understand and Advance Sodium‐Ion Batteries

Considering the natural abundance and low cost of sodium resources, sodium‐ion batteries (SIBs) have received much attention for large‐scale electrochemical energy storage. However, smart structure design strategies and good mechanistic understanding are required to enable advanced SIBs with high energy density. In recent years, the exploration of advanced cathode, anode, and electrolyte materials, as well as advanced diagnostics have been extensively carried out. This review mainly focuses on the challenging problems for the attractive battery materials (i.e., cathode, anode, and electrolytes) and summarizes the latest strategies to improve their electrochemical performance as well as presenting recent progress in operando diagnostics to disclose the physics behind the electrochemical performance and to provide guidance and approaches to design and synthesize advanced battery materials. Outlook and perspectives on the future research to build better SIBs are also provided.     

Quantitative analysis of some mechanisms affecting the yield of oxidative phosphorylation: Dependence upon both fluxes and forces

The purpose of this work was to show how the quantitative definition of the different parameters involved in mitochondrial oxidative phosphorylation makes it possible to characterize the mechanisms by which the yield of ATP synthesis is affected. Three different factors have to be considered: (i) the size of the different forces involved (free energy of redox reactions and ATP synthesis, proton electrochemical difference); (ii) the physical properties of the inner mitochondrial membrane in terms of leaks (H⁺ and cations); and finally (iii) the properties of the different proton pumps involved in this system (kinetic properties, regulation, modification of intrinsic stoichiometry).The data presented different situations where one or more of these parameters are affected, leading to a different yield of oxidative phosphorylation.(1) By manipulating the actual flux through each of the respiratory chain units at constant protonmotive force in yeast mitochondria, we show that the ATP/O ratio decreases when the flux increases. Moreover, the highest efficiency was obtained when the respiratory rate was low and almost entirely controlled by the electron supply. (2) By using almitrine in different kinds of mitochondria, we show that this drug leads to a decrease in ATP synthesis efficiency by increasing the H⁺/ATP stoichiometry of ATP synthase (Rigoulet M et al. Biochim Biophys Acta 1018: 91-97, 1990). Since this enzyme is reversible, it was possible to test the effect of this drug on the reverse reaction of the enzyme i.e. extrusion of protons catalyzed by ATP hydrolysis. Hence, we are able to prove that, in this case, the decrease in efficiency of oxidative phosphorylation is due to a change in the mechanistic stoichiometry of this proton pump. To our knowledge, this is the first example of a modification in oxidative phosphorylation yield by a change in mechanistic stoichiometry of one of the proton pumps involved. (3) In a model of polyunsaturated fatty acid deficiency in rat, it was found that non-ohmic proton leak was increased, while ohmic leak was unchanged. Moreover, an increase in redox slipping was also involved, leading to a complex picture. However, the respective role of these two mechanisms may be deduced from their intrinsic properties. For each steady state condition, the quantitative effect of these two mechanisms in the decrease of oxidative phosphorylation efficiency depends on the values of different fluxes or forces involved. (4) Finally the comparison of the thermokinetic data in view of the three dimensional-structure of some pumps (X-ray diffraction) also gives some information concerning the putative mechanism of coupling (i.e. redox loop or proton pump) and their kinetic control versus regulation of mitochondrial oxidative phosphorylation.     

Comparison between the life cycles of two Soleidae, the common sole, Solea solea, and the thickback sole, Microchirus variegatus, in the Bay of Biscay (France)

The life history of two Soleidae, the common sole, Solea solea, and the thickback sole, Microchirus variegatus, were compared in the Bay of Biscay in an attempt to set out factors which could explain settlement styles known to be different between juveniles of each species. Common sole juveniles had been shown to depend on coastal and estuarine nurseries, and the thickback sole to develop in open-sea nurseries, although the spawning grounds and spawning season of both species overlapped (offshore and at springtime, respectively). For this study, data on adult, juvenile and larva distributions were obtained from cruises carried out in the Bay of Biscay during the last decade. In addition, growth rate of larvae and planktonic interval duration, estimated by means of otolith increment analysis, were compared, as well as literature-derived information on behaviour of larvae. By comparing larval features, it appeared that thickback sole did not obtain the advantage of a slightly longer pelagic life span for an increased dispersal, due to an early shift to benthic behaviour. Other evidence was given by more specifically stated distributions that the further and deeper offshore spawning of M. variegatus, compared to S. solea, was a likely key-factor of the juvenile settlement process. This could explain why the thickback sole, contrary to the common sole, never reach coastal areas and thus settle offshore, in waters deeper than 30 m.     

Soybean cultivar variability for nodule formation and growth under drought

Both nodulation and nitrogen fixation in soybean [Glycine max (L.) Merr.] are sensitive to soil drying, which can have important negative effects on yield. An exception to this general response has been the identification of the cultivar Jackson as being drought tolerant for N₂ fixation. The objectives of this research were to examine nodule formation and growth in Jackson among other soybean cultivars in response to soil drying under field conditions. Two field experiments were conducted to examine the genetic variation in the sensitivity of nodule numbers and dry weights to soil drying. Substantial variation among soybean lines was found, and the drought-tolerance trait was demonstrated again in Jackson. Greenhouse experiments were conducted to further analyze the variation of nodulation response to soil water content. The differences among cultivars observed in the field were confirmed in the greenhouse. Importantly, the relative drought insensitivity of N₂ fixation in cultivar Jackson was associated with high individual nodule dry weight under drought conditions, relative to well-watered plants. It was concluded that large variation in nodulation sensitivity to water deficit exists among soybean cultivars and that the response of N₂ fixation rates to drought is related in part to nodule formation and growth.