DnaA protein dependent denaturation of negative supercoiled oriC DNA minicircles

The DnaA protein binds specifically and tightly to oriC supercoiled 641 bp minicircle DNA. The binding of the initiator promoted a partial unwinding of the superhelical oriC minicircle (Mc-oriC). Open complexes are detected either by a change in the linking number or by the sensitivity to the attack of a single strand specific Bal 31 nuclease. The open complex is found only in the presence of the DnaA protein.     

Antimicrobial and Light‐Enhanced Antimicrobial Activities,Cytotoxicity and Chemical Variability of All Tunisian Eryngium Species

This study was performed on all Eryngium species growing in Tunisia in order to evaluate their intra and interspecies variabilities and to investigate their biological activities. These species are used in traditional medicine, and literature about the phytochemical investigations of most of them is scarce. Antimicrobial and light‐enhanced activities were tested against multiresistant microorganisms and extended spectrum beta‐lactamase producing bacteria (ESBL). All studied species showed antimicrobial effect with several MIC values lower than 70 μg/ml. Tested Eryngium species have proven to be a promising source of photoactive compounds, while light‐enhanced activity offers an alternative for the inactivation of pathogenic microorganisms which is currently subjected to a great interest. This is the first report of this activity in genus Eryngium. A significant improvement of antimicrobial activity with UV irradiation was observed, mainly for E. dichotomum, E. ilicifolium and E. triquetrum. Cytotoxicity, studied for the first time for the most species, was evaluated against cancer (J774) and non‐cancer (WI38) human cell lines. Chemical composition of volatile compounds presented in the most active crude extracts (petroleum ether extracts) of the aerial parts was investigated using GC/MS analysis and was submitted to statistical analyses. It revealed their high content of bioactive phytochemicals, particularly oxygenated sesquiterpenes like spathulenol, ledol and α‐bisabolol but also hydrocarbon sesquiterpenes such as β‐bisabolene and copaene, as well as polyacetylene derivatives such as falcarinol. Statistical analyses permitted to evaluate the interrelations between all Tunisian Eryngium species.     

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.     

Dam methylated and hemimethylatedoriC plasmids are replicated symmetrically; a novel and general test of replication symmetry

Summary Deoxyadenosine methylation (dam) of the numerous GATC sequences present in theEscherichia coli origin of chromosomal replication (oriC) has been shown to be important both in vivo and in vitro for efficient initiation of DNA synthesis. Recent in vivo data suggest that initiation is only inefficient when these sequences are hemimethylated. This raises the interesting possibility that initiation may be inefficient because it only takes place on one strand of the template, i.e., replication is asymmetric on hemimethylated DNA. We tested this possibility by a novel and rapid approach which relies on the specificities of the restriction endonucleasesMboI,MboII andDpnI. Although we show that replication takes place equally well on both strands of methylated and hemimethylatedoriC DNA templates, the method should be applicable to the analysis of replication symmetry on most DNA templates which contain methylated deoxyadenosine GATC sequences as part ofMboII restriction sites.     

The E. coli cell surface specifically prevents the initiation of DNA replication at oriC on hemimethylated DNA templates

A particular outer membrane fraction previously defined as possessing specific affinity for the hemimethylated form of the origin of replication of the E. coli chromosome (oriC) is shown to inhibit the initiation of DNA synthesis at this site on hemimethylated DNA templates in vitro. The replication of fully methylated or unmethylated DNA templates is not affected. Also, no inhibition is observed if initiation takes place at random sites on the hemimethylated template. The key inactivation step appears to be membrane inhibition of DnaA initiator protein binding to oriC. Remethylation of the membrane-bound hemimethylated DNA results in reactivation. Our results demonstrate direct involvement of the membrane in the control of DNA replication. We propose that association/dissociation of the origin from the cell membrane is one of the control elements governing interinitiation times in E. coli.     

Chemical Composition and Antimicrobial Activity of the Essential Oil from Aerial Parts and Roots of Eryngium barrelieri Boiss. and Eryngium glomeratum Lam. from Tunisia

The study of chemical composition and biological activity of unexplored essential oils may open new perspectives on their potential use in facing major health concerns such as drug‐resistant infections. The present study investigates the chemical composition and antimicrobial effects of previously unstudied essential oils obtained from genus Eryngium: Eryngium glomeratum Lam . and Eryngium barrelieri Boiss . The chemical compositions of the essential oils from aerial parts and roots of both species were studied using GC and GC/MS analytical technics. The analysis led to the identification of 102 compounds totalizing 85 – 94% of all detected compounds. Essential oils were characterized by the predominance of oxygenated sesquiterpenes. The oils obtained from aerial parts were tested against 36 microbial strains by agar dilution method and showed minimum inhibitory concentrations (MIC) in the range of 2 – 625 μg/ml. A strong antibacterial activity against multiresistant Pseudomonas aeruginosa was observed especially from E. glomeratum essential oil with MIC value up to 2 μg/ml. These findings give significant information about the pharmacological activity of these essential oils, which suggest their potential use to develop new remedies, or as sources of active compounds.     

Initiation of DNA replication in delta cya mutants of Escherichia coli K12

The purified DnaA protein has a high affinity for cyclic AMP (cAMP). Using equilibrium dialysis, we determined the K(A) value for cAMP as 0.819 muM(-1). The number of cAMP binding sites per DnaA protein molecule was calculated to be 1.04. This binding was quite specific for cAMP. ATP was also bound by DnaA protein and inhibited cAMP binding. This inhibition was non-competitive in nature with an inhibition constant (K(i)) of about 8.25 muM. However, in vivo we have found not only that the DnaA protein level is reduced in a cyclase deletion mutant strain, Delta++ cya, but also that DnaA protein is not degraded. The Delta cya mutants of E. coli are unable to continue DNA synthesis in the absence of de novo protein synthesis and the initiation of DNA replication in these mutants takes place from oriC.     

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.