Prediction of stenosis behaviour in artery by neural network and multiple linear regressions

Biomechanics and Modeling in Mechanobiology - Blood flow analysis in the artery is a paramount study in the field of arterial stenosis evaluation. Studies conducted so far have reported the...     

Escherichia coli HdeB is an acid stress chaperone

We cloned, expressed, and purified the hdeB gene product, which belongs to the hdeAB acid stress operon. We extracted HdeB from bacteria by the osmotic-shock procedure and purified it to homogeneity by ion-exchange chromatography and hydroxyapatite chromatography. Its identity was confirmed by mass spectrometry analysis. HdeB has a molecular mass of 10 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which matches its expected molecular mass. We purified the acid stress chaperone HdeA in parallel in order to compare the two chaperones. The hdeA and hdeB mutants both display reduced viability upon acid stress, and only the HdeA/HdeB expression plasmid can restore their viability to close to the wild-type level, suggesting that both proteins are required for optimal protection of the bacterial periplasm against acid stress. Periplasmic extracts from both mutants aggregate at acidic pH, suggesting that HdeA and HdeB are required for protein solubilization. At pH 2, the aggregation of periplasmic extracts is prevented by the addition of HdeA, as previously reported, but is only slightly reduced by HdeB. At pH 3, however, HdeB is more efficient than HdeA in preventing periplasmic-protein aggregation. The solubilization of several model substrate proteins at acidic pH supports the hypothesis that, in vitro, HdeA plays a major role in protein solubilization at pH 2 and that both proteins are involved in protein solubilization at pH 3. Like HdeA, HdeB exposes hydrophobic surfaces at acidic pH, in accordance with the appearance of its chaperone properties at acidic pH. HdeB, like HdeA, dissociates from dimers at neutral pH into monomers at acidic pHs, but its dissociation is complete at pH 3 whereas that of HdeA is complete at a more acidic pH. Thus, we can conclude that Escherichia coli possesses two acid stress chaperones that prevent periplasmic-protein aggregation at acidic pH.     

Bird nest predation in a southern Tunisian oasis habitat: No evidence of “edge effect”

Numerous ornithological studies conducted in patchy habitats have linked high intensity of nest predation with habitat edges. This “edge effect” hypothesis was primarily investigated in temperate, boreal and tropical fragmented forests, and there is a need for investigations from different habitat systems. Here we provide the results of one study on bird nest predation in relation to edge context in one oasis in southern Tunisia. Our aim was to assess the importance of nest predation as a source of nest failure in the studied oasis and to test if the edge effect hypothesis applies in this habitat system. We found that although predation represents an important source of nest failure in all studied species, the edge effect hypothesis does not seem to apply in the studied oasis. Indeed, daily nest predation rate did not vary with edge context for all studied species, which could be explained by the fact that nest predator guild is mainly composed of small species that use oasis interior and edges in similar ways. The effects of predators coming from the surrounding areas do not seem to significantly increase nest predation rates in oasis edges compared to oasis interior. We also found that nest predation rates were similar for all bird species, suggesting that among-species differences in nest concealment and nesting behaviour did not seem to account for nest survival in the studied oasis. However, further more detailed species-level studies are needed to test this hypothesis and to identify more accurately the determinants of nest predation in the oasis habitat.     

Association of Lymphotoxin Alpha Polymorphism with Type 1 Diabetes in a Tunisian Population

We investigated the association of the lymphotoxin (LT)-α gene polymorphism +249A/G with type 1 diabetes. The distribution of genotypes of the LT-α +249A/G single nucleotide polymorphism (SNP) was assessed in 115 diabetic patients and 123 normoglycemic control subjects, using PCR-restriction fragment length polymorphism analysis. Among unselected patients, the SNP was significantly associated with increased risk of diabetes (χ² = 8.44, p = 0.014) and was found to be more pronounced among female (χ² = 8.37, p = 0.02) than male (χ² = 6.11, p = 0.047) patients. A significant association was detected between LT-α +249A/G and increased risk of diabetes, in particular for young-onset patients (χ² = 6.92, p = 0.031). Moreover, we reported significant differences in levels of HbA1c, triglycerides, alanine transaminase, and anti-glutamic acid decarboxylase-65 among alleles. Additional studies with extended patient age groups and different ethnicities are needed to confirm our findings.     

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

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 Gabès, 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 composition (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.     

Factors affecting bird richness in a fragmented cork oak forest in Morocco

The cork oak forest of Ma'amora in north-western Morocco was the largest cork oak forest in the world until the beginning of the 20th century. Due to growing land use for agriculture and urbanization, however, this forest has become fragmented into relatively small and isolated patches. The effects of this fragmentation on the diversity of wild animal communities have never been investigated despite the importance of such investigations in elaborating long-term conservation plans of the biodiversity of this forest system. In this study of a sample of 44 forest patches we assessed the relationships between species numbers of wintering, breeding and spring migrant birds and patch size, shape, isolation and vegetation structure. We found that species richnesses of the three studied bird assemblages were strongly related to local vegetation structure, namely to the diversity and abundance of trees and bushes. Patches with higher diversity and cover of trees and bushes support higher numbers of bird species. However, patch size, shape and isolation were not significant predictors of bird richness. These results suggest that bird communities in the studied forest patches were more likely shaped by local habitat suitability rather than the amount of habitat or patch isolation. The results also demonstrate negative effects of current human pressures, namely logging, grazing and disturbance, on the diversity of bird communities in this forest system. This emphasizes the need for urgent management efforts aiming at reducing the negative impacts of forest use by humans on bird diversity in this forest system.     

Towards novel Cry toxins with enhanced toxicity/broader: a new chimeric Cry4Ba / Cry1Ac toxin

Attempts have been made to express or to merge different Cry proteins in order to enhance toxic effects against various insects. Cry1A proteins of Bacillus thuringiensis form a typical bipyramidal parasporal crystal and their protoxins contain a highly conserved C-terminal region. A chimerical gene, called cry(4Ba-1Ac), formed by a fusion of the N-terminus part of cry4Ba and the C-terminus part of cry1Ac, was constructed. Its transformation to an acrystalliferous B. thuringiensis strain showed that it was expressed as a chimerical protein of 116 kDa, assembled in spherical to amorphous parasporal crystals. The chimerical gene cry(4Ba-1Ac) was introduced in a B. thuringiensis kurstaki strain. In the generated crystals of the recombinant strain, the presence of Cry(4Ba-1Ac) was evidenced by MALDI-TOF. The recombinant strain showed an important increase of the toxicity against Culex pipiens larvae (LC₅₀ = 0.84 mg l^?1 ± 0.08) compared to the wild type strain through the synergistic activity of Cry2Aa with Cry(4Ba-1Ac). The enhancement of toxicity of B. thuringiensis kurstaki expressing Cry(4Ba-1Ac) compared to that expressing the native toxin Cry4Ba, might be related to its a typical crystallization properties. The developed fusion protein could serve as a potent toxin against different pests of mosquitoes and major crop plants.