Changes in Membrane Fatty Acid Composition of Pseudomonas aeruginosa in Response to UV-C Radiations

The changes in lipid composition enable the micro-organisms to maintain membrane functions in the face of environmental fluctuations. The relationship between membrane fatty acid composition and UV-C stress was determined for mid-exponential phase and stationary phase Pseudomonas aeruginosa. The total lipids were obtained by dichloromethane/methanol (3:1) and were quantified by GC. The TLC analysis of phospholipids showed the presence of three major fractions phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin. Significant modifications, as manifested by an increase of UFA, were obtained. Interestingly, this microorganism showed a remarkable capacity for recovery from the stressful effects of UV-C.     

Toxicity assessment of the puffer fish Lagocephalus lagocephalus from the Tunisian coast

This study was undertaken to assess the risk of poisoning due to consumption of the puffer fish Lagocephalus lagocephalus collected along the Tunisian coast. Wistar rats were daily intraperitoneally injected, for 10 days, with acidic extracts of liver or flesh (muscles + skin) of L. lagocephalus. Control rats received injections of NaCl (0.9%). No mortality and no evident signs of neurotoxicity were recorded in treated rats. Conversely, treatment led to: (1) diarrhoea and body and organ (liver, kidney) weights loss; (2) oxidative stress evidenced by an increase in lipid peroxidation (TBARS) and conversely a decrease in antioxidant enzyme activities (SOD, catalase, GSH-Px) in tissues (blood cells, liver, kidneys); (3) a decrease in alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities in blood plasma.     

Dual Valorization of Olive Mill Wastewater by Bio‐Nanosynthesis of Magnesium Oxide and Yarrowia lipolytica Biomass Production

This research investigates an efficient dual valorization of olive mill wastewater in the biosynthesis of magnesium oxide nanoparticles and in the depollution of the effluent by Yarrowia lipolytica growth evaluation. After removal of polyphenols, the recovered biophenols were reacted with the magnesium precursor to provide magnesium oxide nanoparticles. In order to confirm the biosynthesized magnesium oxide nanoparticles, several analyses were undertaken. The Fourier transform infrared spectrum gives a broad absorption at 658 cm^?1 confirming the presence of the magnesium oxide nanoparticles, while the UV/VIS absorption spectroscopy reveals an intense transition with a maximum absorption at 300 nm. The X‐ray diffraction and transmission electron microscopy analyses show that nanoparticles are in pure cubic crystalline with spherical and hexagonal shapes (average size is 19.4 nm). The zeta potential analysis illustrates a negative potential proving a good stability of the biosynthesized nanoparticles. Nanoparticles were assigned for their in vitro antibacterial activity against Escherichia coli, Enterobacter aerogenes, Salmonella typhimurium, Staphylococcus cohnii, and Bacillus niacini. The evaluation of the growth of Yarrowia lipolytica on the recovered olive mill wastewater after removal of polyphenols yielded 3.2 g/L of the Yarrowia biomass in 72 h without nutriment additions, providing an important decrease of chemical oxygen demand (73 %).     

The effect of methylation on DNA replication in Salmonella enterica serovar typhimurium

The DNA adenine methylase of Salmonella typhimurium methylates adenine at GATC sequences. Strains deficient in this methylase are not well transformed by methylated plasmids, but unmethylated plasmids transform them at high frequencies. Hemimethylated daughter molecules accumulate after the transformation of dam(-) strains with fully methylated plasmids, suggesting that hemimethylation prevents DNA replication. It will also be shown that plasmids isolated from dam(-) bacteria are hemimethylated by restriction enzyme digestion. These results may explain why newly formed daughter molecules are not substrates for immediate reinitiation of DNA replication in dam(-) bacteria.     

Cohabitation within mice of Salmonella typhimurium seqA mutant increases its virulence

The efficacy of a vaccine is conditioned by its capacity to elicit a protective immune response. The principal safety concerns of live vaccine are virulence reversion. The aim of this work was to evaluate the virulence of Salmonella typhimurium seqA mutant after cohabitation with mice. Our results indicated that LD50 of hosted strains were at least twofold lower than those of parental strains. Also, the in vivo competition assays have showed that the development of a systemic infection was most obvious for recovered strains than for control strains. In addition, the number of hosted mutants colonizing spleen and liver was relatively higher than control strains. Adhesion and invasion experiments were performed in order to compare the pathogenicity of Salmonella. For instance recovered-mutant attached to epithelial cells (KB cells) better than parental strains. According to these results, we report that in vivo adaptation of Salmonella typhimurium seqA mutants can increase their virulence.     

Effects of hydrogen peroxide on the motility, catalase and superoxide dismutase of dam and/or seqA mutant of Salmonella typhimurium

In addition to their role in the virulence attenuation of Salmonella and other pathogens, dam or seqA genes increase the sensitivity towards hydrogen peroxide. The aim of our study is to investigate the effect of H₂O₂ on the motility, the catalase and superoxide dismutase activities of dam and/or seqA mutants of Salmonella typhimurium. Our findings showed significant differences of the effects of H₂O₂ on the motility between wild type strain and all of mutants. Hydrogen peroxide changes SOD isoenzyme profile of these mutants by disappearance of Fe-SOD. Concerning the catalase, an increase of its activity was observed in the wild type, dam and seqA mutant. However, H₂O₂ decreases the activity of this enzyme in the double mutant strain. We can suggest that the dam gene, together with seqA, play a protective role in the oxidative stress response of Salmonella typhimurium.     

Karyotypic variation in two species of jerboas Jaculus jaculus and Jaculus orientalis (Rodentia, Dipodidae) from Tunisia

The karyotypes of the lesser Egyptian jerboa Jaculus jaculus and the greater Egyptian jerboa Jaculus orientalis from Tunisia are described and compared with available data particularly from Egypt. The species examined have a similar karyotype consisting of 2n = 48 chromosomes and a fundamental number of autosomes (NFa) varying from 88 to 90 in J. jaculus and from 84 to 88 in J. orientalis. The X chromosome is submetacentric in both species, while the Y is submetacentric in J. orientalis and acrocentric in J. jaculus. Most of the autosomes are meta/submetacentric but the small pairs 22 - 23 in J. jaculus and 20-23 in J. orientalis are frequently acrocentric, yielding considerable differences in the NFa within and among species. Morphological variation in these small pairs of autosomes and/or in the Y chromosome in J. orientalis may distinguish populations of the two species from Egypt and Tunisia. The differences observed either between Egypt and Tunisia or between the Tunisian Jaculus species are probably associated with chromosomal rearrangements such as pericentric inversions or heterochromatin variation. They appear of lesser magnitude than other changes (especially molecular) that have occurred during the evolution of this genus.     

The DNA-methylation state regulates virulence and stress response of Salmonella

The DNA methylation is a post-replicative event that provides secondary information to that formed by DNA. Addition of this information involves DAM methyltransferase, which methylates DNA on specific sites (5'-GATC-3'). This modification of DNA may play a role in regulating various processes in eukaryote or prokaryote cells. It was well understood that deoxyadenosine methyltransferase (DAM) methylates the adenine of the GATC sequence. Following DNA replication, however, DNA is transiently hemimethylated, and the new strand is then methylated by DAM. In Escherichia coli, removing the dam gene produces several phenotypes indicating multiple functions of methylation: (i) modulation of gene expression, (ii) DNA repair, (iii) initiation of replication, and (iv) stabilising the chromosome.