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.     

Multiple cysteine residues are implicated in Janus kinase 2-mediated catalysis

The redox regulation of Janus kinase 2 (JAK2) is poorly understood, and there are contradictory reports as to whether the enzyme's activity is inhibited or stimulated by oxidizing conditions in the cell. Here we demonstrate that multiple cysteine residues within the JAK2 catalytic domain may be crucial for enzymatic activity. The enzyme is catalytically inactive when oxidized; activity can be restored via reduction to the thiol state. A series of recombinant variants of JAK2 were overproduced using the baculoviral expression vector system. A truncated variant of JAK2, GST/(NDelta661)rJAK2, provided evidence that the amino-terminal autoinhibitory domain was not essential for direct redox regulation and that only nine cysteine residues were potentially involved. The effect of individually and combinatorially altering these nine cysteines was examined via cysteine-to-serine mutagenesis. This identified four cysteine residues in the catalytic domain (Cys866, Cys917, Cys1094, and Cys1105) that cooperatively maintain JAK2's catalytic competency. Our data are consistent with a direct mechanism for redox regulation of JAK2 via oxidation and reduction of critical cysteine residues.     

Phospholipid changes in seqA and dam mutants of Escherichia coli

SeqA and Dam proteins were known to be responsible for regulating the initiation of replication and to affect the expression of many genes and metabolisms. We have examined here the fatty acids composition and phospholipids membrane in dam and/or seqA mutants. The dam mutant showed an accumulation of the acidic phospholipids cardiolipin, whereas, the seqA mutant showed a higher proportion of phosphatidylglycerol compared with the wild-type strain. The seqA dam double mutant showed an intermediate proportion of acidic phospholipids compared with the wild-type strain. Based on these observations, we discuss the role of Dam and SeqA proteins in the regulation of phospholipids synthesis.     

Hemitoxin, the first potassium channel toxin from the venom of the Iranian scorpion Hemiscorpius lepturus

Hemitoxin (HTX) is a new K+ channel blocker isolated from the venom of the Iranian scorpion Hemiscorpius lepturus. It represents only 0.1% of the venom proteins, and displaces [125 I]alpha-dendrotoxin from its site on rat brain synaptosomes with an IC50 value of 16 nm. The amino acid sequence of HTX shows that it is a 35-mer basic peptide with eight cysteine residues, sharing 29-69% sequence identity with other K+ channel toxins, especially with those of the alphaKTX6 family. A homology-based molecular model generated for HTX shows the characteristic alpha/beta-scaffold of scorpion toxins. The pairing of its disulfide bridges, deduced from MS of trypsin-digested peptide, is similar to that of classical four disulfide bridged scorpion toxins (Cys1-Cys5, Cys2-Cys6, Cys3-Cys7 and Cys4-Cys8). Although it shows the highest sequence similarity with maurotoxin, HTX displays different affinities for Kv1 channel subtypes. It blocks rat Kv1.1, Kv1.2 and Kv1.3 channels expressed in Xenopus oocytes with IC50 values of 13, 16 and 2 nM, respectively. As previous studies have shown the critical role played by the beta-sheet in Kv1.3 blockers, we suggest that Arg231 is also important for Kv1.3 versus Kv1.2 HTX positive discrimination. This article gives information on the structure-function relationships of Kv1.2 and Kv1.3 inhibitors targeting developing peptidic inhibitors for the rational design of new toxins targeting given K+ channels with high selectivity.     

Microgeographical distribution of two chromosomal races of house mice in Tunisia: pattern and origin of habitat partitioning.

Two chromosomal races of the house mouse occur in Tunisia, a standard morph (40St) found all over the country, and a derived morph (22Rb) occurring only in central Tunisia. In this region, habitat partitioning between the two morphs was investigated by a microgeographical analysis of their distribution, assessing habitat characteristics and demographic parameters. Results showed that the 22Rb mice always occurred in the oldest sections of towns (medinas), often extending to more recent surrounding neighbourhoods where the 40St morph was most abundant. The latter was never trapped within the medinas. The transition between the two morphs was located within cities in the more recent areas, the hybrid zone being estimated at less than 0.5 km in width by a clinal analysis of chromosomal data. Although differences between habitats exist, almost no demographic differences were found between populations of the two morphs when they occurred in the same or in different habitats. Two hypotheses are discussed to account for the origin of habitat partitioning. The first relies on competitive exclusion of the 40St mice from the medinas by the derived 22Rb mice; the second is based on stochastic processes related to historical evolution of Tunisian urban communities.     

Mitochondrial DNA variation in the caramote prawn <Emphasis Type="Italic">Penaeus (Melicertus) kerathurus</Emphasis> across a transition zone in the Mediterranean Sea

In this study we analysed mitochondrial DNA variation in Penaeus kerathurus prawns collected from seven locations along a transect across the Siculo–Tunisian region in order to verify if any population structuring exists over a limited geographical scale and to delineate the putative transition zone with sufficient accuracy. Partial DNA sequences of COI and 16S genes were analysed. In contrast to the highly conservative 16S gene, the COI sequences exhibited sufficient diversity for population analysis. The COI gene revealed low levels of haplotype and nucleotide diversities. The size of the annual landings of this commercial species suggests large population sizes. Hence, the low genetic diversity detected in this study could indicate a possible reduction in effective population sizes in the past. We detected significant genetic differentiation between eastern and western populations likely due to restricted gene flow across the Siculo–Tunisian boundary. We discuss the different evolutionary forces that may have shaped the genetic variation and suggest that the genetic divide is probably maintained by present-day dispersal limitation. R. Zitari-Chatti and N. Chatti are contributed equally to the work.     

Comparative Assessment of SSR and AFLP Markers for Evaluation of Genetic Diversity and Conservation of Fig, <Emphasis Type="Italic">Ficus carica</Emphasis> L., Genetic Resources in Tunisia

This study characterises the genetic variability of fig, Ficus carica L., using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers. It compares the efficiency and utility of the two techniques in detecting variation and establishing genetic relationships among Tunisian fig cultivars. Our results show that using both marker systems, the Tunisian fig germ plasm is characterised by having a large genetic diversity at the deoxyribonucleic acid level, as most of AFLP bands were detected and all SSR markers were polymorphic. In fact, 351 (342 polymorphic) and 57 (57 polymorphic) bands were detected using AFLP and SSR primers, respectively. SSR markers were the most polymorphic with an average polymorphic information content value of 0.94, while AFLP markers showed the highest effective multiplex ratio (56.9) and marker index (45.2). The effective marker index was recorded highest (4.19) for AFLP markers and lowest (0.70) for the SSR ones. Our results demonstrate that (1) independent as well as combined analyses of cluster analyses of SSR and AFLP fragments showed that cultivars are clustered independently from their geographical origin, horticultural classifications and tree sex; (2) the analysis of molecular variance allowed the partitioning of genetic variation within and among fig groups and showed greater variation within groups and (3) AFLP and SSR markers datasets showed positive correlation. This study suggests the SSR and AFLP markers are suitable for diversity analysis and cultivars fingerprinting. An understanding of the genetic diversity and population structure of F. carica in Tunisia can also provide insight into the conservation and management of this species.     

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 %).