Showing papers by "Tunis University published in 2007"

BACTIBASE: a new web-accessible database for bacteriocin characterization

Abstract: Background Bacteriocins are very diverse group of antimicrobial peptides produced by a wide range of bacteria and known for their inhibitory activity against various human and animal pathogens. Although many bacteriocins are now well characterized, much information is still missing or is unavailable to potential users. The assembly of such information in one central resource such as a database would therefore be of great benefit to the exploitation of these bioactive molecules in the present context of increasing antibiotic resistance and natural bio-preservation need.

The global diabetes pandemic: the Tunisian experience

Abstract: The prevalence of diabetes mellitus is known to be increasing rapidly worldwide, but few population-based surveys have been undertaken in Africa or the Middle East. The aims of this study are to report the prevalence of diabetes mellitus and impaired fasting glucose (IFG) in Tunisia, to compare the prevalence to previous studies and to analyse the relationship between diabetes and age, sex, area of residency and body mass index (BMI). We have used data from the Tunisian National Nutrition Survey, a cross-sectional health study providing a large nationally representative sample of the Tunisian population including 3729 adults. We used the American Diabetes Association diagnostic criteria to determine the prevalence of diabetes mellitus and IFG. The overall diabetes prevalence was 9.9% (9.5% in men and 10.1 in women) giving age-adjusted prevalence of diabetes of 8.5% (7.3% in men and 9.6% in women). Step-wise logistic regression showed age of more than 40 years, urban residency and high BMI to each be significantly and independently related to diabetes prevalence. The prevalence of diabetes mellitus has more than doubled in Tunisia over a 15-year period. Our study has demonstrated a high prevalence of diabetes in the adult population with a wide difference among the rural and urban areas with an increased prevalence compared to previous studies. The results underline the need to increase public awareness and to emphasize the benefit of lifestyle modification in order to prevent type II diabetes.

Association of GST genes polymorphisms with asthma in Tunisian children.

Abstract: Background. A positive association between genetic polymorphism and asthma may not be extrapolated from one ethnic group to another based on intra- and interethnic allelic and genotype frequencies differences. Objective. We assessed whether polymorphisms of GST genes (GSTM1, GSTT1, and GSTP1) are associated with asthma and atopy among Tunisian children. Methods. 112 unrelated healthy individuals and 105 asthmatic (73 atopic and 32 nonatopic) children were studied. Genotyping the polymorphisms in the GSTT1 and GSTM1 genes was performed using the multiplex PCR. The GSTP1 ILe105Val polymorphism was determined using PCR-RFLP. Results. GSTM1 null genotype was significantly associated with the increased risk of asthma (P = .002). Asthmatic children had a higher prevalence of the GSTP1Ile105 allele than the control group (43.8% and 33.5%, respectively; P = .002). Also, the presence of the GSTP1 homozygote Val/Val was less common in subjects with asthma than in control group. We have found that GSTT1 null genotype (GSTT1 *0/*0) was significantly associated with atopy (P = .008). Conclusion. Polymorphisms within genes of the GST superfamily were associated with risk of asthma and atopy in Tunisia.

Selective catalytic reduction of NO by ammonia on V2O5-SO42-/TiO2 catalysts prepared by the sol-gel method

Abstract: This paper examines the effect of sulfation of vanadia-titania binary solid prepared by sol-gel process on its activity for the selective catalytic reduction (SCR) of NO with NH3. Sulfated and unsulfated vanadia titania have been characterized by means of N-2 adsorption-desorption at 77 K, XRD, TGA, propan-2-ol conversion as acid test, H-2-TPR measurements, EPR, XPS and Raman spectroscopies. The main results of this study highlight the interaction of sulfate ions with vanadia species. The ternary catalyst VTiS exhibits a high activity compared to binary TiS or VTi samples. It is concluded that sulfate species improve the superficial acidity of solid and interact with vanadia leading to a better reducibility of VTiS oxide. (c) 2006 Elsevier B.V. All rights reserved.

Diffusion Limit of a Semiconductor Boltzmann–Poisson System

Abstract: The paper deals with the diffusion limit of the initial‐boundary value problem for the multidimensional semiconductor Boltzmann–Poisson system. Here, we generalize the one‐dimensional results obtained in [5] to the case of several dimensions using global renormalized solutions. The method of moments and a velocity averaging lemma are used to prove the convergence of the renormalized solutions to the semiconductor Boltzmann–Poisson system towards a global weak solution of the drift‐diffusion‐Poisson model.

Genetic diversity of Tunisian figs (Ficus carica L.) as revealed by nuclear microsatellites.

Abstract: The present study portrays the achievement of the genetic polymorphism surveying and the establishment of an ecotypes identification key on the basis of simple sequence repeats data. Seventy-two Tunisian fig ecotypes in situ and ex situ conserved were analyzed using six microsatellite loci. A total of 58 alleles and 124 genotypes were revealed and permitted to evidence high degree of genetic diversity mainly explained at the intra group level. Cluster analysis based on genetic distances proved that a typical continuous genetic diversity characterizes the local germplasm. In addition, the microsatellite multilocus genotyping has permitted to unambiguously distinguish 70 well-defined ecotypes (resolving power of 97.22%). Data are discussed in relation with the reliability of the used markers to check the conformity of the plant material and to rationally manage the conservation of this crop.

Interspecific potato somatic hybrids between Solanum berthaultii and Solanum tuberosum L. showed recombinant plastome and improved tolerance to salinity

Abstract: In this study three somatic hybrid lines originating from protoplast fusion between Solanum tuberosum cv. BF15 and Solanum berthaultii were subjected to a detailed molecular analysis using the I-SSR-PCR technique based on 5′-anchored microsatellite primers. The data obtained revealed a polymorphism between the different lines, suggesting that they correspond to symmetric hybrids. The analysis of chloroplast genome of these hybrids showed that they are resulting from a recombination between parental plastomes. When transferred to a greenhouse, these hybrid lines displayed an improved vigour compared to the cultivated potato BF15 parent. Indeed, an important growth rate and high tuber yield and weight were obtained for these hybrids compared to the parent. Some of these hybrids showed also an improved ion homeostasis control and they seem to display a better tolerance to salt stress compared to the potato BF15 parent.

Nanorod B phase VO2 obtained by using benzylamine as a reducing agent

Abstract: Vanadium dioxide nanorod B phase with high purity and crystallinity was synthesized by using the crystalline V2O5 as precursor and benzylamine for the first time as reducing agent via hydrothermal method. The structure and morphology of the sample were characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, thermal analysis and infrared spectroscopy. Regularly sized nanorod B phase VO2 is about 20–100 nm wide and up to 2.5m long. © 2006 Elsevier B.V. All rights reserved.

Morphological evaluation of cork oak (Quercus suber): Mediterranean provenance variability in Tunisia

Abstract: Twenty-six provenances (2 340 plants) of cork oak (Quercus suber spp.) originating from Portugal, Spain, Italy, Morocco, Algeria, and Tunisia were tested for genetic variation among and within provenances by growth traits. Seven morphometrical characters were measured in 90 plants from each provenance. Analysis of variance showed highly significant differences for all characters. The phenotypic coefficient of differentiation reached 0.24 for the form and 0.22 for height, thus revealing a strong structuring between the provenances. Comparative study of growth among the provenances revealed more vigorous growth and better survival rate for those from Morocco, Spain, and Portugal, which may constitute better materials for afforestation. Furthermore, this variability appeared to be geographically structured and would be mainly genetically controlled, as cork oak provenances were cultivated under the same environmental conditions. Our results should be helpful for guide forest managers in afforestation.

Synthesis and characterization of mesoporous silica-supported nano-crystalline sulfated zirconia catalysts prepared by a sol–gel process: Effect of the S/Zr molar ratio

Abstract: Mesoporous silica-supported nano-crystalline sulfated zirconia catalysts were prepared via the sol–gel process using an in situ sulfation. The parameter studied in this work was the S/Zr molar ratio. The synthesized solids were characterized using XRD, N 2 physisorption, TG-DTA/SM, sulfur chemical analysis and adsorption–desorption of pyridine, and tested in the gas-phase acid-catalysed isomerization of n -hexane. The gelation process is highly affected by the sulfate loadings. Two gelation mechanisms were evidenced depending on the S/Zr molar ratio. The first one observed when 0.15 ≤ S/Zr ≤ 0.5, is characterized by a relatively high gelation rate. This mechanism favours the formation of two types of mesopores and a low percentage of retained sulfur. The second gelation mechanism occurs for higher S/Zr ratios: 0.5 ≤ S/Zr ≤ 1.2. In that case, slower gelation rates are observed. This slower gelation process leads to materials with reduced BET surface area but the amount of retained sulfur is increased. Appreciable catalytic properties were observed for the sample prepared with the highest S/Zr ratio, which presents the smallest size of sulfated zirconia crystallites and shows both Bronsted and Lewis acid sites on its surface.

Genetic diversity of Rhynchosporium secalis in Tunisia as revealed by pathotype, AFLP, and microsatellite analyses

Abstract: Genetic variability among 122 Rhynchosporium secalis isolates collected from barley in three regions of Tunisia was investigated using host differentials, amplified fragment length polymorphism (AFLP), and microsatellite markers. The isolates were collected from a widely grown scald-susceptible barley cultivar Rihane and a range of local landrace cultivars in geographically distinct regions with different agroclimatic conditions. Pathotypic diversity (the proportion of unique pathotypes) was high in R. secalis populations from the high (100% diversity), moderate (95%), and low (100%) rainfall areas of Tunisia, and from both Rihane (which is the sole variety grown in the high rainfall region) and local landraces (which predominate in the low rainfall area). This may reflect a general adaptability for aggressiveness and suggests that the widely grown cultivar Rihane has exerted little or no selection pressure on the pathogen population since its release in 1983. Genotypic diversity (GD), defined as the probability that two individuals taken at random had different genotypes, was high for populations from Rihane, local landraces, and different agro-ecological zones (GD = 0.96–0.99). There was low genetic differentiation among pathogen populations from different host populations (G ST ≤ 0.08, θ ≤ 0.12) and agro-ecological zones (G ST ≤ 0.05, θ ≤ 0.04), which may be partly explained by gene flow due to the movement of infected stubble around the country. There was no correlation (r = 0.06, P = 0.39) between virulence phenotype and AFLP haplotype. A phenetic tree revealed groups with low bootstrap values that did not reflect the grouping of isolates based on host, pathotype, or agro-ecological region. The implications of these findings for R. secalis evolutionary potential and scald-resistance breeding in Tunisia are discussed.

Rhizobial inoculation and p fertilization response in common bean (phaseolus vulgaris) under glasshouse and field conditions

Abstract: Osmotic constraints, nutrient deficiencies, especially phosphorus, and the lack of efficient strains of rhizobia in Mediterranean soils are major factors limiting symbiotic nitrogen fixation and yield in common bean (Phaseolus vulgaris). In order to improve yields, we investigated responses to rhizobial inoculation and P fertilization under glasshouse and field conditions with two bean cultivars, Coco blanc and BAT477. The nodulation test, using a hydroponic system in a glasshouse, revealed strong variability among 22 rhizobium strains of various origins, in their symbiotic efficiency, compared with Rhizobium tropici CIAT899. The introduced strains proved to be more efficient although some local rhizobia revealed high potential efficiencies. Glasshouse trials showed a significant effect of inoculation and P supply on nodulation, N content and shoot dry weight that varied with rhizobial strain. Field trials substantiated the glasshouse observations and emphasized the effects of cultivar-rhizobia interactions on symbiotic parameters and yields. It is concluded that inoculation with suitable rhizobia with supply of additional P is a technology that may improve symbiotic nitrogen fixation and yield in common bean in some soils under a Mediterranean climate.

Comparative studies of the structure, morphology and electrical conductivity of polyaniline weakly doped with chlorocarboxylic acids

Abstract: We report the results of studies on two series of polyaniline (PANI), doped with dichloroacetic (DCA) and trichloroacetic (TCA) acids, respectively, at various doping rates and obtained by the in situ polymerization method. Samples were characterized by x-ray diffraction, scanning electron microscopy and conductivity measurements. The direct current (dc) and alternating current (ac) electrical conductivities of PANI salts have been investigated in the temperature range 100–310 K and frequency range 7–106 Hz. The results of this study indicate better chain ordering and higher conductivity for PANI doped with TCA. The dc conductivity of all samples is suitably fitted to Mott's three-dimensional variable-range hopping (VRH) model. Different Mott parameters such as characteristic temperature T0, density of states at the Fermi level (N(EF)), average hopping energy (W) and the average hopping distance (R) have been evaluated. The dependence of such values on the dopant acid used is discussed. At high frequencies, the ac conductivity follows the power law σac(ω,T) = A(T)ωs(T,ω), which is characteristic for charge transport in disordered materials by hopping or tunnelling processes. The observed increase in the frequency exponent s with temperature suggests that the small-polaron tunnelling model best describes the dominant ac conduction mechanism. A direct correlation between conductivity, structure and morphology was obtained in our systems.

Vigilance in Greater Flamingos Wintering in Southern Tunisia: Age-Dependent Flock Size Effect

Abstract: Decrease in individual vigilance with flock size is a widely recognized pattern in group-living species. However such a relationship may be affected by other factors, such as age and flock composition. For instance, because young animals generally lack experience and have higher nutritional needs than adults, they can be expected not only to be less vigilant than adults but also to decrease their vigilance level by a greater extent when flock size increases than adults do. We investigated this issue using data on greater flamingos wintering in the gulf of Gabes, in southern Tunisia. Flamingos tended to congregate in small single-age flocks for feeding, but as flock size increased, flocks became mixed. We found that when flock size increased, young flamingos significantly decreased their vigilance time, while adult did not, suggesting an age- dependent flock size effect on vigilance. However, when flock composi- tion (single-age vs. mixed) was taken into account, a more complex pattern was found. Within single-age and small flocks, no difference was found between young flamingos and adult ones regarding their vigilance level and their response to increasing flock size. However, within mixed and large flocks, adult flamingos were more vigilant than young ones, while variation in flock size did not result in a significant change in vigilance. These results suggest that young birds relied on the presence of adults, and hence more experienced individuals in detecting dangers, to reduce their vigilance and to increase their foraging time in order to satisfy their higher nutritional requirements. They could also be interpreted as a possible consequence of increasing competition with flock size which constrained more nutritionally stressed young flamingos to increase their foraging time to the detriment of vigilance.

Structure versus relaxor properties in Aurivillius type compounds

Abstract: Structure refinements in M II Bi 4 Ti 4 O 15 (M II = Ca, Ba), Bi 4− x Ba x Ti 3− x Nb x O 12 , (Na 0.5 Bi 0.5 ) 1− x Ba x Bi 4 Ti 4 O 15 and Bi 4 Ti 3 O 12 –PbTiO 3 systems are used to report structural features of relaxor Aurivillius phases. In compounds with relaxor-like behaviour, the average structure is almost undistorted, closed to the archetypal HT paraelectric phase, with a tolerance factor ≳0.996. The coordination number of Bi 3+ in fluorite layers changes from {4 + 2} for ferroelectrics to {4} for relaxors. Transmission Electron Microscopy reveals some characteristic features of relaxors such as micro-twinning, shearing-type defects which attest from the existence of a compositional inhomogeneity and a disorder at a local scale.