Biomedical subjects

S Maisnier-Patin

Publications and source records attributed to S Maisnier-Patin.

8 recordsLinked to original sources

PubMed2001

Replication arrests during a single round of replication of the Escherichia coli chromosome in the absence of DnaC activity.

We used a flow cytometric assay to determine the frequency of replication fork arrests during a round of chromosome replication in Escherichia coli. After synchronized initiation from oriC in a dnaC(Ts) strain, non-permissive conditions were imposed, such that active DnaC was not available during elongation. Under these conditions, about 18% of the cells failed to complete chromosome replication. The sites of replication arrests were random and occurred on either arm of the bidirectionally replicating chromosome, as stalled forks accumulated at the terminus from both directions. The forks at the terminal Ter sites disappeared in the absence of Tus protein, as the active forks could then pass through the terminus to reach the arrest site, and the unfinished rounds of replication would be completed without DnaC. In a dnaC2(Ts)rep double mutant, almost all cells failed to complete chromosome replication in the absence of DnaC activity. As inactivation of Rep helicase (the rep gene product) has been shown to cause frequent replication arrests inducing double-strand breaks (DSBs) in a replicating chromosome, DnaC activity appears to be essential for replication restart from DSBs during elongation.

Base Sequence↗

PubMed2001

RecA-mediated rescue of Escherichia coli strains with replication forks arrested at the terminus.

The recombinational rescue of chromosome replication was investigated in Escherichia coli strains with the unidirectional origin oriR1, from the plasmid R1, integrated within oriC in clockwise (intR1(CW)) or counterclockwise (intR1(CC)) orientations. Only the intR1(CC) strain, with replication forks arrested at the terminus, required RecA for survival. Unlike the strains with RecA-dependent replication known so far, the intR1(CC) strain did not require RecBCD, RecF, RecG, RecJ, RuvAB, or SOS activation for viability. The overall levels of degradation of replicating chromosomes caused by inactivation of RecA were similar in oriC and intR1(CC) strains. In the intR1(CC) strain, RecA was also needed to maintain the integrity of the chromosome when the unidirectional replication forks were blocked at the terminus. This was consistent with suppression of the RecA dependence of the intR1(CC) strain by inactivating Tus, the protein needed to block replication forks at Ter sites. Thus, RecA is essential during asymmetric chromosome replication for the stable maintenance of the forks arrested at the terminus and for their eventual passage across the termination barrier(s) independently of the SOS and some of the major recombination pathways.

Bacterial Proteins↗

PubMed2000

New genes with old modus operandi. The connection between supercoiling and partitioning of DNA in Escherichia coli.

The process of partitioning bacterial sister chromosomes into daughter cells seems to be distinct from chromatid segregation during eukaryotic mitosis. In Escherichia coli, partitioning starts soon after initiation of replication, when the two newly replicated oriCs move from the cell centre to quarter positions within the cell. As replication proceeds, domains of the compact, supercoiled chromosome are locally decondensed ahead of the replication fork. The nascent daughter chromosomes are recondensed and moved apart through the concerted activities of topoisomerases and the SeqA (sequestration) and MukB (chromosome condensation) proteins, all of which modulate nucleoid superhelicity. Thus, genes involved in chromosome topology, once set aside as 'red herrings' in the search for 'true' partition functions, are again recognized as being important for chromosome partitioning in E. coli.

Bacterial Outer Membrane Proteins↗

PubMed1998

Conversion to bidirectional replication after unidirectional initiation from R1 plasmid origin integrated at oriC in Escherichia coli.

The cell division phenotypes of Escherichia coli with its chromosome replication driven by oriR (from plasmid R1) were examined by fluorescence microscopy and flow cytometry. Chromosome replication patterns in these strains were followed by marker frequency analyses. In one of the strains, the unidirectional oriR was integrated so that the replication fork moved clockwise from the oriC region, and bacterial growth and division were similar to those of the wild-type parent. The bacteria were able to convert the unidirectional initiation from oriR into bidirectional replication. The site for conversion of uni- to bidirectional replication seemed to be localized and could be mapped genetically within 6 min to the immediate right of the minimal oriC. Replication starting in the counterclockwise direction from the R1 replicon integrated at the same site in the opposite orientation could not be described as either bi- or unidirectional, as no single predominant origin could be discerned from the more or less flat marker frequency pattern. These strains also showed extensive filamentation, irregular nucleoid distribution and the presence of anucleate cells, indicative of segregation and division defects. Comparison among intR1 derivatives differing in the position of the integrated oriR relative to the chromosome origin suggested that the oriC sequence itself was dispensable for the conversion to bidirectionality. However, passage of the replication fork over the 6 min region to the right of oriC seemed important for the bidirectional replication pattern and normal cell division phenotype.

Cell Division↗

PubMed1996

Cell wall changes in nisin-resistant variants of Listeria innocua grown in the presence of high nisin concentrations.

Two nisin-resistant variants of a strain of Listeria innocua were isolated after growth in the presence of 500 and 4000 IU ml-1 of nisin A showed increased cell wall hydrophobicity, resistance to phage attack and three different cell wall-acting antibiotics, as well as to the peptidoglycan hydrolytic enzymes lysozyme and mutanolysin, as compared to the parental strain. Transmission electron microscopy revealed marked thickening of the wall of nisin-resistant cells with an irregular surface. Differences in thickness were lost after cell wall purification and no significant difference in gross wall composition was observed between the parental and resistant variants. Cell wall changes in nisin-resistant listeriae are attributed to abnormal cell wall synthesis and autolysin inhibition, the latter possibly associated with subtle changes in cell wall structures and function.

Anti-Bacterial Agents↗

PubMed1996

Purification, partial characterisation and mode of action of enterococcin EFS2, an antilisterial bacteriocin produced by a strain of Enterococcus faecalis isolated from a cheese.

Enterococcus faecalis strain EFS2, isolated from the surface of a traditional cheese, produced a bacteriocin active against Gram-positive bacteria including Listeria spp. and some Staphylococcus aureus strains. The bacteriocin, named enterococcin EFS2, has been purified to homogeneity by ammonium sulphate precipitation and reversed-phase high performance liquid chromatography (RP-HPLC). The molecular weight was determined by mass spectrometry to be 7149.6. The amino acid composition of enterococcin EFS2 revealed that it contained 67 amino acid residues and had a blocked amino-terminal end. Enterococcin EFS2 induced viability loss, efflux of K+ ions and ATP, and cell lysis. Kinetic study of bactericidal activity of enterococcin EFS2 on Listeria innocua strain LIN11 indicated slower cell destruction than by nisin. At pH 7.0, the activity of enterococcin EFS2 was the highest at 35 degrees C and was lost at 15 degrees C. The bacteriocin was more active against L. innocua strain LIN11 in broth adjusted to pH 6.0, 7.0 and 8.0 than to pH 4.5 at 30 degrees C.

Amino Acids↗

PubMed1995

Activity and purification of linenscin OC2, an antibacterial substance produced by Brevibacterium linens OC2, an orange cheese coryneform bacterium.

An orange cheese coryneform bacterium isolated from the surface of Gruyère of Comté and identified as Brevibacterium linens produces an antimicrobial substance designated linenscin OC2. This compound inhibits gram-positive food-borne pathogens including Staphylococcus aureus and Listeria monocytogenes but is not active against gram-negative bacteria. Linenscin OC2 caused viability loss and lysis of the test organism, Listeria innocua. Electron microscopy showed that linenscin OC2 induces protoplast formation and cell lysis. The native substance is resistant to proteolytic enzymes, heat, and organic solvents and stable over a wide range of pH. The molecular weight of the native linenscin OC2 was estimated by gel chromatography to be over 285,000. Linenscin OC2 was purified by ammonium sulfate precipitation, 2-propanol extraction, and reverse-phase chromatography. Direct detection of antimicrobial activity on a sodium dodecyl sulfate-polyacrylamide gel suggested an apparent molecular mass under 2,412 Da. Molecular mass was determined to be 1,196.7 Da by mass spectrometry. Amino acid composition analysis indicated that linenscin OC2 may contain 12 residues.

Amino Acids↗

PubMed1994

Isolation and identification of cheese-smear bacteria inhibitory to Listeria spp.

A newly developed hydrophobic grid membrane method was used to rapidly screen 105 traditional French cheeses for surface smear microorganisms inhibitory to Listeria monocytogenes strain V7. Approximately 125,000 colonies comprising a wide variety of bacteria were examined of which less than 0.1% produced visible zones of inhibition. Isolates possessing antilisterial activity consisted of various strains of Enterococcus faecalis, Staphylococcus xylosus, Staphylococcus warneri and coryneform bacteria, including one orange coryneform resembling Brevibacterium linens. All strains of E. faecalis and the orange coryneform that inhibited L. monocytogenes V7 exhibited strong inhibition against a panel of 21 Listeria strains comprised of L. monocytogenes (14 strains), L. innocua (two strains), L. ivanovii (two strains), L. seeligeri (two strains) and L. welshimeri (one strain). The remaining cheese isolates showed moderate to weak inhibition towards the same set of Listeria strains. Inhibitory substances produced by all strains except the orange coryneform were sensitive to one or more of five proteolytic enzymes tested and were therefore classified as bacteriocin-like inhibitory agents.

Actinomycetales↗