dam methylation and the initiation of DNA replication on oriC plasmids

Summary Plasmid DNA containing the replication origin of the Escherichia coli chromosome (oriC) has been shown to be inefficient as a template for DNA synthesis in vitro when isolated from dam mutants. here, we extend this study to hemimethylated oriC plasmids and to replication in dam-3 mutant enzyme extracts. The results show that: (1) hemimethylated oriC plasmids replicate with the same low efficiency as nonmethylated DNA; (2) DNA synthesis starts at oriC regardless of the methylated state of the template; (3) replication in dam-3 enzyme extracts is inefficient because this strain is deficient in DnaA protein; and (4) consistent with this observation, the copy number of the oriC plasmid pFH271 is reduced in the dam-3 mutant. However, we have found that low DnaA protein levels in dam-3 mutants are not sufficient to explain the reduced transformation efficiency of oriC plasmids. We suggest that there must exist in vivo inhibitory factors not present or present in low quantities in vitro which specifically recognize the hemimethylated or nonmethylated forms of the oric region.     

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.     

Review – Interactions between diatoms and stainless steel: focus on biofouling and biocorrosion

There is a considerable body of information regarding bacterially enhanced corrosion, however, this review focuses on diatoms (unicellular algae) whose contribution to biocorrosion is less well studied. The reasons why diatoms have been neglected in studies of biocorrosion in natural waters are discussed and the question whether diatoms should be considered as inert with respect of electrochemical processes is considered. A particular focus is given to the case of stainless steels (SS), which are widely used in variety of applications in natural waters. Basic information on the cell biology of diatoms is included in the review, particularly with respect to their ability to ‘sense’ and adhere to surfaces. Investigations at the nanoscale are reviewed as these studies provide information about the behavior of cells at interfaces. Recent advances include the use of atomic force microscopy (AFM), although only a few studies have been applied to diatoms. Regarding the electrochemical behavior of SS, the mechanisms by which diatoms influence the potential ennoblement process is discussed. Such studies reveal the association of diatoms, in addition to bacteria, with biocorrosion processes.     

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.     

YajL, prokaryotic homolog of parkinsonism-associated protein DJ-1, functions as a covalent chaperone for thiol proteome

YajL is the closest Escherichia coli homolog of the Parkinsonism-associated protein DJ-1, a multifunctional oxidative stress response protein whose biochemical function remains unclear. We recently reported the aggregation of proteins in a yajL mutant in an oxidative stress-dependent manner and that YajL exhibits chaperone activity. Here, we show that YajL displays covalent chaperone and weak protein oxidoreductase activities that are dependent on its exposed cysteine 106. It catalyzes reduced RNase oxidation and scrambled RNase isomerization and insulin reduction and forms mixed disulfides with many cellular proteins upon oxidative stress. The formation of mixed disulfides was detected by immunoblotting bacterial extracts with anti-YajL antibodies under nonreducing conditions. Disulfides were purified from bacterial extracts on a YajL affinity column, separated by nonreducing-reducing SDS-PAGE, and identified by mass spectrometry. Covalent YajL substrates included ribosomal proteins, aminoacyl-tRNA synthetases, chaperones, catalases, peroxidases, and other proteins containing cysteines essential for catalysis or FeS cluster binding, such as glyceraldehyde-3-phosphate dehydrogenase, aldehyde dehydrogenase, aconitase, and FeS cluster-containing subunits of respiratory chains. In addition, we show that DJ-1 also forms mixed disulfides with cytoplasmic proteins upon oxidative stress. These results shed light on the oxidative stress-dependent chaperone function of YajL and identify YajL substrates involved in translation, stress protection, protein solubilization, and metabolism. They reveal a crucial role for cysteine 106 and suggest that DJ-1 also functions as a covalent chaperone. These findings are consistent with several defects observed in yajL or DJ-1 mutants, including translational defects, protein aggregation, oxidative stress sensitivity, and metabolic deficiencies.     

YajL, the prokaryotic homolog of the Parkinsonism-associated protein DJ-1, protects cells against protein sulfenylation

YajL is the closest Escherichia coli homolog of the Parkinsonism-associated protein DJ-1, a multifunctional oxidative stress response protein whose biochemical function remains unclear. We recently described the oxidative-stress-dependent aggregation of proteins in yajL mutants and the oxidative-stress-dependent formation of mixed disulfides between YajL and members of the thiol proteome. We report here that yajL mutants display increased protein sulfenic acids levels and that formation of mixed disulfides between YajL and its protein substrates in vivo is inhibited by the sulfenic acid reactant dimedone, suggesting that YajL preferentially forms disulfides with sulfenylated proteins. YajL (but not YajL(C106A)) also forms mixed disulfides in vitro with the sulfenylated form of bovine serum albumin. The YajL-serum albumin disulfides can be subsequently reduced by glutathione or dihydrolipoic acid. We also show that DJ-1 can form mixed disulfides with sulfenylated E. coli proteins and with sulfenylated serum albumin. These results suggest that YajL and possibly DJ-1 function as covalent chaperones involved in the detection of sulfenylated proteins by forming mixed disulfides with them and that these disulfides are subsequently reduced by low-molecular-weight thiols.     

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 %).     

Aerobic Biodegradation of DDT by Advenella Kashmirensis and Its Potential Use in Soil Bioremediation

The aim of this study was to select a bacterial strain able to degrade 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT), and to use it for bioaugmentation in order to decontamination soil. Advenella Kashmirensis MB-PR (A. Kashmirensis MB-PR) was isolated from DDT contaminated soil, and the degradation ability of DDT by this strain in the mineral salt medium was screened by gas chromatography. The efficiency of degradation was 81% after 30 days of bacterial growth. The study of intermediary products during the degradation of DDT showed the appearance and accumulation of DDD and DDE, which emerged from the first days of the experiment. Other metabolites were detected at a lower number of chlorine atoms, such as DBH. DNA samples were isolated and screened for the linA gene, encoding dehydrochlorinase. The bioaugmentation by A. Kashmirensis MB-PR of polluted sterile soil showed that 98% of DDT disappeared after 20 days of experience. This study demonstrates the significant potential use of A. Kashmirensis MB-PR for the bioremediation of DDT in the environment.     

Contribution of silver nanoparticles to extend <Emphasis Type="Italic">Salmonella typhimurium</Emphasis> growth under various respiration regimes

Living cells interact with different forms of metal; the resulted biochemical alteration depends on the dose. Over an average dose in ionic form, metals interact with respiration processes at various levels, and it induces oxidative stress by shifting the whole oxydoreduction equilibrium. To correct the toxicity, cell develops different ways to cancel the effect of the exceeded charges, and it reduces the ion to get a more stable form. In the case of nanoparticles, the reactivity of surface has been enhanced that can alter the biological mechanisms; the cell may develop different strategies to minimize this reactivity. The current study is focused on the pursuing of cell behavior regarding the presence of nanoparticles and their associated metals. Nanoparticles have been synthesized using bio-reducing agents and then were structurally characterized using X-ray diffraction, UV–Vis, and infra-red spectroscopy. The oxydoreduction flexibility of the post-synthesis modified nanoparticles was tested in vitro. Interactions with cells were done using Salmonella under various respiration conditions. The final results show the possible correction of oxidative stress effects and the recuperation of respiration.