Impact of crop management on intraspecific diversity of Pseudomonas corrugata in bulk soil.

The genetic structure of Pseudomonas corrugata populations was investigated in bulk soil to evaluate the impact of crop management on the intraspecific diversity of this bacterium stimulated in plant rhizosphere. As these bacteria are rare in bulk soil, an immunotrapping assay was developed to isolate them from soils located in Grignon (France), where adjacent plots with similar soil features were cultivated under maize/wheat crop rotation or continuous wheat cropping. Genomic fingerprinting of 291 isolates was performed using repetitive sequence-based polymerase chain reaction (ERIC-PCR). Most of these isolates (236 out of 291) were assigned to P. corrugata on the basis of an amplified ribosomal DNA restriction analysis (ARDRA) with 12 restriction enzymes. Data were analyzed by Pearson's chi-squared tests and genetic diversity was evaluated with specific indices for richness and evenness. Comparison of richness or evenness diversity indices (global diversity) showed no significant difference, whereas ERIC-PCR fingerprinting data (intraspecific diversity) showed that the genetic structure of P. corrugata was significantly affected by crop management.

Lethal effects of mexel 432, an antifouling agent, on embryolarval development of common carp (Cyprinus carpio L.).

Embryolarval lethal effects of Mexel 432, an antifouling agent, were determined in the laboratory during continuous exposure, beginning at fertilization, under various experimental conditions in eight different spawns of the common carp (Cyprinus carpio L). In synthetic water at 24 degrees C and without larval feeding, correlations between LC50 values and the various experimental conditions tested, except Mexel 432 concentration, were low. The mean LC50 values were 1.13+/-0.35 mg/liter after 3 days of exposure and 0.88+/-0.36 mg/liter after 7 days. In five spawns, it was 0. 69+/-0.32 mg/liter after 9 days. The lowest and highest LC50 values were 0.34 and 1.58 mg/liter after 7 days of exposure. Sensitivity to Mexel 432 increased slightly from the egg to the newly hatched larva and the developed larva. No lethality was observed during a period of recuperation after 4 days of exposure. The toxicity of Mexel 432 was not strongly reduced after 15 days of conservation of the solution. Vessel walls pretreated with Mexel 432 revealed no toxicity by contact or after eventual desorption. Methodological endpoints such as criteria for spawn quality, experimental conditions for the tests, demonstration of cumulative effects, and toxicometric importance of the period of mortality by starvation in fish early life toxicity tests are discussed.

Deltamethrin multifactorial activity toward carp larva mobility related to calcium, humic acids, and pH.

The toxicity of pyrethroid insecticide deltamethrin was assessed by the "escaping capability" of carp larvae out of a trap. Mobility was tested after 1, 4, and 12 hr exposure to eight deltamethrin concentrations in standard water and after 24 hr exposure to seven deltamethrin concentrations in 18 media derived from the combinations of pH levels of 6.9, 7.8, 9.0, calcium concentrations of 2 . 10(-4) and 2 . 10(-2) M, and humic acid concentrations on 0, 5 and 100 mg/liter. In standard water, a 1-hr exposure at 4 microg/liter deltamethrin increased the mobility, while a 4-hr 32 microg/liter exposure decreased it. After 24 hr without deltamethrin, mobility was reduced at pH 6.9 and 7.8 and 2 . 10(-4) M calcium. It was also reduced in 100 mg/liter humic acids, especially when the former pH and calcium conditions were used. Humic acid effects could partly result from a calcium concentration reduction in water, and darkness due to humic acid coloration could play a minor role. Increasing humic acid concentration, calcium concentration, and pH reduced deltamethrin activity. In 0 or 5 mg/liter humic acids the No Observed Effect Concentration was 1 microg/liter, and in 100 mg/liter humic acid it was 2 microg/liter. Compared to previous results on deltamethrin-induced lethality, the escape test appeared less reproducible, but was 2 or 4 times more sensitive.

Deltamethrin lethal multifactorial activity toward carp larva related to pH, calcium, and humic acid concentrations.

Acute 24-hr embryotoxicity of the pyrethroid insecticide delta-methrin toward carp larvae was tested in multifactorial combinations of three pHs (6.9, 7.8, 9.0), two calcium concentrations ([Ca] = 2 x 10(-4) and 2 x 10(-2) M), and three humic acids concentrations ([HA] = 0, 5, and 100 mg/liter). Lethal effects were determined and compared to the distribution and hexane extractibility of radiolabeled deltamethrin in the solution and on the vessel walls, either in the presence or in the absence of the larvae. As a function of the three combined factors tested, the no observed effect concentrations (NOECs) differed to a maximum by a factor of 8, while they differed by only a factor of 2 with pH alone, and by a factor of 4 with calcium or humic acids alone. No contact toxicity was observed with adsorbed deltamethrin on the vessel walls, on which adsorption and hexane extractibility was increased in the presence of larvae. The most plausible interpretation for the toxicological influence of the physicochemical factors tested on deltamethrin toxicity deals with the deltamethrin distribution in the medium for humic acids, changes in biological targets for calcium influence, and, for pH influence, degradation speed or one of the two other explanations.

Toxic effects, at three pH levels, of two reference molecules on common carp embryo.

Early life-stage survival, motility, and growth toxicity tests were carried out on common carp (Cyprinus carpio L.) endotrophic embryo, with two reference molecules (captafol and DNOC), from fertilization to the end of the first two-thirds period of mortalities by starvation. Thirteen days duration exposure was performed in daily renewed medium, at 24.5 degrees C, in standard synthetic water, at three pHs (6.9, 7.8, 9.0), in the presence of 10 mM/liter nontoxic pH buffer. Nominal concentrations of toxicants were 0.0, 0.25, 0.5, 1.0, and 2.0 mg/liter. Toxic effects on survival, motility, and growth decreased with increasing pH. From pH 6.9 to 9.0, the "no-observed-effect concentrations" differed by a factor greater than 8. Motility and growth cannot be considered, at population level, as true sublethal embryo-larval toxicity criteria. The toxicological interpretation of these results is discussed. They confirm the need of multifactorial methods for toxic risks and effects assessment on fish early life stages in the environment.

Stabilization of oversaturated aqueous solutions of deltamethrin, a highly lipophilic molecule.

The stability of oversaturated solutions of the highly lipophilic molecule deltamethrin under the conditions of continuous agitation and oxygenation by air bubble flow in a toxicologic test on fish embryos was studied. In polyethylene, glass, and Teflon containers, the 24-hr adsorption rate of 1 mg/l solutions was over 80%. Improvement by Sharon and Solomon's PEG-glass pretreatment did not exceed a small percentage. After agarose precoating, the adsorption rate in the glass or polyethylene containers was reduced to about 20%. The stabilizing effect of precoating agarose containers diminished with the concentration of the solution.

Incidence of (n-3) essential fatty acid deficiency on trout reproductive processes.

A feeding experiment was conducted on rainbow trout broodstock for one year to investigate the influence of the quality of dietary lipids on egg and fry fatty acid composition, embryonic development and hatching efficiency. The broodstock were fed either a commercial control diet or a (n-3) fatty acid-deficient diet; their liver, eggs and fry were analysed to determine the fatty acid composition of their neutral and polar lipids. The fatty acid pattern in liver, eggs and fry was markedly different due to the qualitative difference of the dietary lipids. The most striking difference was the low amount of 22:6 (n-3) and the high levels of 20:4 (n-6) and 22:5 (n-6) in phospholipids of fish receiving the (n-3)-deficient diet containing a high level of 18:2 (n-6). While fertilization efficiency was equivalent in the first two days of development, whatever the diet, two peaks of mortality were observed, one at day 8 and the other at day 22 after fertilization, during the time the eggs produced by the deficient fish were incubated. A shorter period of vitellus resorption (50 vs 65 day) was observed in (n-3)-deficient alevins as compared to controls. Morphological study of the development of the (n-3)-deficient embryos showed some cleavage disorders at the 16 to 32-cell stage, a blocking effect before gastrulation, and later various alterations in organogenesis. It was concluded that (n-3) fatty acids, and especially 22:6 (n-3), play a crucial and specific role in trout embryo development. These fatty acids could be involved in cellular recognition processes through their oxygenated derivatives. The need for long-term nutritional deficiency to induce the reported biochemical and physiological alterations is discussed.

[Clonal multiplication and mitotic capacity]. / Multiplication clonale et capacité mitotique.

On a theoretical model of cellular genome we demonstrate that the clonal multiplication induces an ineluctable decline of the "mitotic capacity". A cellular population is formed, the genomes of which include no more than one of each fundamental genetic element.

[Vital cycle, mitotic capacity, and genomic restoration]. / Cycle vital, capacité mitotique et restauration génomique.

We define a theoretical model for clonal reproduction and we describe how the accumulation of mutations induces an ineluctable decline of the "mitotic capacity". During the vital cycle of organisms, meïosis and fecundation may have the function of making up for this fall. This should allow us to understand the temporal structure or the sexualisation of the vital cycle as well as some peculiarities of the spatial structure of the genome.

Membrane differentiation in the pregastrula of the teleost, Brachydanio rerio Hamilton-Buchanan (Teleostei: Cyprinidae). A scanning electron microscope study.

The pregastrula stages of the teleost, Brachydanio rerio, have been studied in intact or fractured eggs by scanning electron microscopy. The internal surface of the enveloping blastomeres was smooth, while the external surface was covered with cristae; these cristae disappeared during epiboly but reappeared when the cells were in mitosis. At the end of the morula stage, the smooth yolk cytoplasmic layer formed a ring of periblastic cristae; up to the late blastula stage that ring was attached to "star-like" complexes. Light and transmission electron microscopy images of these complexes are given and we propose hypotheses regarding their function. At first closely apposed, the deep cells seemed to be maximally dispersed during the mid-blastula stage. At the blastula stage, the yolk syncitium formed both enveloping and deep cells. This suggests a primordial role of the yolk syncitium layer in pregastrula differentiation. A new hypothesis concerning the functions of the membrane protrusions is proposed: they might play a role in the postmiotic reassociation of the blastomeres. We suggest that, during early development, the three modes of cell association, i.e. monolayer, mass aggregation, syncitium, might be correlated with the composition of the three media (perivitelline liquid, blastocoelic liquid, yolk) present at that time.

[Histochemical localization of lactate dehydrogenase in the trout embryo (Salmo irideus, Gibb) during early organogenesis of the cord and the neural tube]. / Localisation histochimique de la lacticodéshydrogénase dans l'embryon de la truite (Salmo iredeus, Gibb), au cours de l'organogenése précoce de la corde et du tube neural

The histochemical study of the LDH in the Trout embryo during the early organogenesis shows a specific localization in notochord cells, in mesodermic cells of the terminal knob and in some prosencephalic neuroblasts. The role of the LDH in the metabolism of NAD as well as in the energetic metabolism of embryonic cells is discussed.

[Histochemical localization of lactate dehydrogenase in blastomeres during early development of the rainbow trout embryo (Salmo irideus Gibb)]. / Localisation histochimique de la lacticodéshydrogénase dans les blastomères au cours du développement précoce de l'embryon de la truite arc-en-ciel (Salmo irideus Gill)

During the early development of the trout egg, some blastomers display a certain activity of the L.D.H., variable according to their position in the embryo. At the morula stage, the histochemical ltion of those blastomeres. On the contrary, during the gastrula stage, the blastomeres which have a high L.D.H. activity concentrate in the deep layer of the germ, in the "embryonic button", and in the germinal ring.