Effects of mercury on soil microbial communities in tropical soils of French Guyana

In gold mining regions, the risk of soil pollution by mercury is a major environmental hazard, especially in tropical areas where soil microflora plays a major part in soil functioning, major bio-geochemical cycles and carbon turn-over. The impact of mercury pollution on soil microflora should thus be carefully assessed in such environments while taking into consideration the specificities of tropical soils. The aim of this study was to compare the effects of mercury (0, 1 and 20 μg of inorganic mercury per gram of soil) on the functional diversity and genetic structure of microbial communities in a tropical soil. We investigated the effects of mercury on tropical soil microflora using soil microcosms spiked with mercury and incubated at 28 °C for 1 month. Microcosm flora, its biomass and its activity, as well as its functional and genetic structure, were followed by cultural methods, measures of respiration, ECOLOG plates, and DGGE (denaturing gel gradient electrophoresis), respectively. Fate of total and bioavailable mercury was estimated by CVAFS (cold vapor atomic fluorescence spectrometry). Results obtained for the microcosms enriched with only 1 μg g^?1 mercury were indistinguishable from controls. Conversely, in the presence of high mercury contents (20 μg g⁽¹), an immediate effect was measured on soil respiration, functional diversity (ECOLOG plates) and genetic structure (DGGE), although no significant effect was observed on plate counts or microbial biomass. In addition, whereas microbial activities (respiration and functional diversity) rapidly regained control values, a lasting effect of the high mercury concentration was observed on the genetic structure of the soil microbial community. These modifications took place during the first week of incubation when total mercury concentration was declining and bioavailable mercury was at its highest.This multiple approach study is one of the first attempts at investigating the effects of mercury on soil microbial communities in tropical soils. Our results demonstrate that in the tropical soil under study, mercury affects the soil microbial communities in a different manner than was previously reported in temperate soils. Furthermore, mercury toxicity on soil microbes may be modulated by typical tropical soil characteristics.     

Effect of ABA,arginine and sucrose on protein content of date palm somatic embryos

Abscisic acid (ABA), arginine and sucrose were evaluated for their effects on the morphology, germination rates and protein content of date palm somatic embryos (SE). Different concentrations of these supplements in the culture medium were used. The comparative study of SE length and thickness between treated and untreated SE revealed no differences, except for ABA (20 μM), which increased thickness. A decrease of water content (WC) in favor of an increase in dry weight (DW) was observed in all treated SE, especially with sucrose (90 g l⁻¹) and ABA (20 μM). Only ABA (20 and 4 μM) caused a proliferation rate of the cultures higher than those in the control. Although all the tested compounds increased protein content, ABA (20 μM) was more effective in protein enrichment than arginine and sucrose treatments. The SDS-PAGE protein profiles showed a significant difference between treated and untreated SE. A protein band of 22 kDa, identified as glutelin in a previous work, was accumulated after treatment with 20 μM ABA or 3 mM arginine. These findings may contribute to further understanding of the mechanisms involved in the accumulation of specific storage proteins in several plants.     

Biochemical and histological effects of gibberellic acid on Locusta migratoria migratoria fifth instar larvae

Experiments were conducted to assess the effect of gibberellic acid (GA₃), a plant growth regulator, on Locusta migratoria migratoria fifth instar larvae. Newly emerged larvae were exposed to various concentrations of GA₃ administered by topical application or by forced ingestion. Results showed that treated insects exhibited toxic symptoms with a dose-dependent mortality. GA₃ toxicity was also demonstrated by perturbation of the moult processes. In fact, we noted that treated insects present exuviations difficulties due to the impossibility to reject the old integuments causing mortality in the 5th instar larvae. Histological study of proventriculus revealed alterations in the epithelial cells and absence of apolysis phenomenon. Data also showed that GA₃ induced significant quantitative variation of haemolymph metabolites. These changes result in a significant decrease in the total concentration of proteins and carbohydrates and an increase in the total concentration of haemolymph lipids.     

Diflubenzuron and oogenesis in the codling moth,Cydia pomonella (L.)

Diflubenzuron, topically applied (0·5 μg insect^?-1) to Cydia pomonella (L.) at pupal ecdysis disturbed growth and development of oocytes. It delayed the adult ecdysis and caused a decrease in both thickness of the follicular epithelium and the size of the basal oocyte during the pupal development. On the other hand, the size of basal oocytes, the protein content per ovary and the number of oocytes per ovary recorded in newly emerged adults were significantly reduced after diflubenzuron treatment. These results, together with observations in several other species, indicate that the reduction in fecundity and egg viability is probably due to interference of diflubenzuron with the vitellogenesis process.     

Phylogenetic relationships in grey mullets (Mugilidae) in a Tunisian lagoon

The Mugilidae family is an important fish group representing a major source for fisheries and aquaculture. In the south Mediterranean bank, no data are available on this fauna, except for some morphological studies on Tunisian samples. In this study, 16 allozymic loci were used to investigate the phylogenetic relationships within Tunisian mugilids. The results obtained from Hergla lagoon samples highlight five operational taxonomic unit corresponding to the well‐known species (Liza aurata, Liza ramada, Liza saliens, Chelon labrosus, Mugil cephalus). Several loci appeared to be diagnostic of these species, but in contrast to Greek mugilid samples, we did not find any diagnostic locus fixed differently for the five species. These results can help aquaculture units to identify accurately the mullet species they subsequently use for stocking aquaculture ponds and inland waters. However, species identity represents very important information, as each species has a different growth rate and salinity tolerance. On the other hand, when compared with North Mediterranean Mugilidae analysed until now, Tunisian samples show a genetic differentiation that could be related to different physicochemical conditions between the North and South banks, similar to those recorded in the eastern and western two Mediterranean basins separated by the Siculo‐Tunisian strait. In addition, this study confirms the morphological taxonomy, except for the subdivision of the Liza genus into two sub‐genera. The phylogenetic tree is in agreement with that on Languedoc Mugilidae samples (France), indicating that the subdivision of the Liza genus into two sub‐genera appears to be without any genetic base.     

Occurrence of naphtho-gamma-pyrones- and ochratoxin A-producing fungi in French grapes and characterization of new naphtho-gamma-pyrone polyketide (aurasperone G) isolated from Aspergillus niger C-433

A survey on the occurrence on grape of fungi species in 2001 and their capability to produce ochratoxin A (OTA) and naphtho-gamma-pyrones (NGPs) was conducted in different vineyards from several French viticulture regions. The total numbers of fungal isolates, from setting to harvest, were 732. The Aspergillus genus was essentially represented by section Nigri (98.53%) and it was predominant (74.72%) when compared to Penicillium (25.27%). Approximately one third (30.46%) of the fungal isolates were OTA producers, and 94.17% belong to black aspergilli; Aspergillus carbonarius was the main OTA producer. Moreover, 8.33% of isolates (belong to A. carbonarius and A. niger) were NGP producers. However, none of the Penicillium spp. or other Aspergillus spp. isolates can produces NGP derivatives under the conditions used. No other study on NGPs production by fungi isolated from grapes has been reported. In the second part, a novel NGP, named aurasperone G (1), was isolated from the fermentation broth of the culture extracts of Aspergillus niger C-433, strain producer of OTA, along with the known compound aurasperone F (2). The chemical structure of the new polyketide was proposed based on complete (1)H and partial (13)C, COSY, HMQC, 1D NOE NMR spectra as well as UV and MS spectra. This new NGP was not reported before in nature or prepared synthetically.     

Determination of relationships between the ultrasound velocity and the physical properties of bovine cortical bone femur

BACKGROUND: Accurate measurements of physical characteristics of bone are essential for diagnosis, assessment of change following treatment, and therefore, indirectly, for evaluation of new forms of therapy. This is particularly true of osteoporosis and aging skeleton, in which fractures occur easily. METHODS: In this study an ultrasonic system was set-up and calibrated on Plexiglas tubes of variable thickness then used to detect the cortical bone thickness change in calf and bovine adult femurs. Lamb waves have been generated and detected using a pair of Piezoelectric point transducers (transmitter and receiver) operating at 60 kHz in contact with the surface of the bone. RESULTS: A link has been established between the ultrasound velocity and the bone thickness. On the other hand, the density variation has been also investigated by the simulation of the bone decalcification chemically. The results show that the velocity is very sensitive to both thickness and density, its value reduces as the cortical bone thickness and density decrease. CONCLUSION: This technique might be considered in the attendance of certain bone diseases expressing itself by gradual change in physical properties.     

Uptake and distribution of three insect growth regulators — diflubenzuron, flucycloxuron and halofenozide — in pupae and adults ofTenebrio molitor

In a topical bioassay with pupae and adults of the mealwormTenebrio molitor (Coleoptera: Tenebrionidae), an important pest in stored products worldwide, three insect growth inhibitors (IGRs) were tested: the two chitin synthesis inhibitors diflubenzuron and flucycloxuron, and the ecdysone agonist halofenozide (RH-0345). To address differences in toxicity, we determined with the use of a¹⁴C-labeled isotope, the pattern of absorption through the cuticle and then the distribution in the different body tissues of gut, hemolymph, integument and reproductive organs (ovaries, testis). The rate of absorption through the cuticle was highest for flucycloxuron, and this concurred with its high toxicity. In general, the patterns of absorption followed a similar trend in young and old pupae and in the adult stage. Accumulation in the reproductive system of females and males was relatively high, which may explain the strong reproductive effects of the IGRs tested. In addition, we recorded large differences in the clearance of insecticide from the insect bodyvia the excrements, with the chitin synthesis inhibitors exhibiting higher rates than halofenozide.     

Effects of gibberellic acid on ovarian biochemical composition and ecdysteroid amounts in the migratory locust Locusta migratoria (Orthoptera,Acrididae)

Migratory locusts represent the most important crop pests in Africa and Asia. Because environmental damages are associated with the use of synthetic insecticides in locust and grasshopper control, new environmentally acceptable approaches are becoming increasingly important. The effects of gibberellic acid (GA₃), a plant growth regulator, was investigated by topical application and ingestion on the reproductive physiology and ecdysteroids production of the migratory locust Locusta migratoria at concentrations of 125, 625, 3125, 4125, 5125 and 6125 μg/mL. The treatment applied to adult females during the pre-ovipositional phase provokes a significant adverse influence on their reproductive potential. Indeed, GA₃ significantly reduced both fecundity and fertility. Gibberellic acid also caused disturbances in the incorporation of the hemolymph metabolites (proteins, carbohydrates and lipids) in the oocyte resulting in a significant reduction in their concentrations in the ovaries. Ecdysteroid production was measured by an enzymo-immunoassay. GA₃, administered by ingestion to the adult females, significantly reduced the ecdysteroid titers in ovaries and freshly laid eggs.