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B Labedan

Publications and source records attributed to B Labedan.

At least 37 records · Page 2Linked to original sources
PubMed1988

Increase in permeability of Escherichia coli outer membrane by local anesthetics and penetration of antibiotics.

The MICs of several antibiotics (both hydrophobic and hydrophilic) which penetrate very poorly into intact Escherichia coli cells were found to be 2- to 10-fold decreased in the presence of low doses of various local anesthetics (procaine, dibucaine, tetracaine, chlorpromazine, and quinine). The concentrations of anesthetics necessary for this effect have no adverse effect on cell growth and are markedly lower than those concentrations used clinically.

Aminoglycosides↗
PubMed1985

Involvement of calcium in the transient depolarization of E.coli cytoplasmic membrane induced by phage adsorption: a study with the fluorescent calcium indicator QUIN2.

Adsorption of phage T4 to its outer membrane receptor (the lipopolysaccharide) triggers a transient depolarization of the cytoplasmic membrane which is prevented upon addition of EGTA, suggesting that calcium is necessary for the transmission of the signal between the two membranes. Using the fluorescent indicator QUIN2, we show that T4 adsorption triggers the release of envelope-bound calcium, the amount of which increases with the number of infecting phages. Since this amount was the same whether the cells were pretreated or not with EDTA-Tris, this suggests that this calcium originated from the high affinity sites of the lipopolysaccharide.

Adsorption↗
PubMed1985

The energetics of the injection process of bacteriophage lambda DNA and the role of the ptsM/pel-encoded protein.

We have examined the nature of the role played in the process of phage lambda DNA injection by the bacterial protein coded by the ptsM/pel gene. Neither the specific inhibition of the activity of the PtsM protein, nor the addition of inhibitors of phosphotransferase system modified the efficiency of lambda DNA penetration. Thus, the PtsM/Pel protein does not seem to play a role through its transport function, although we have confirmed that it must be present for a successful lambda DNA injection. Moreover, the presence of various metabolic inhibitors (uncouplers, cyanide, arsenate) separately or together, or even harsher methods of energy depletion did not prevent lambda DNA penetration, suggesting that DNA is entering the cell cytoplasm by diffusion.

Bacterial Proteins↗
PubMed1985

Release of respiratory control in Escherichia coli after bacteriophage adsorption: process independent of DNA injection.

Adsorption of phages T4, T5, and BF23 to previously starved Escherichia coli cells triggered the immediate release of respiratory control. A similar stimulation of respiration was induced after T4 ghost attachment, showing that this process was independent of the mechanism of DNA injection. Rather, this change in the respiratory rate was related to the transient depolarization of the cytoplasmic membrane also induced after phage and ghost adsorption. Both processes were suppressed by addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the case of T4 (phage and ghosts) but not of T5 and BF23. The increase in respiratory rate observed after phage adsorption was of a magnitude similar to that induced by protonophores. Since other treatments that depolarize the membrane without a massive proton influx did not increase the rate of respiration of starved bacteria with the same efficiency, these results suggest that phage adsorption induced an entry of protons into the cell cytoplasm.

Adsorption↗
PubMed1984

Involvement of envelope-bound calcium in the transient depolarization of the Escherichia coli cytoplasmic membrane induced by bacteriophage T4 and T5 adsorption.

We previously showed that adsorption of bacteriophages T4 and T5 to their respective outer membrane receptors induced a partial depolarization of the cytoplasmic membrane. As these membrane potential changes were independent of phage properties, we proposed that phage adsorption triggered the emission of a signal which must be transmitted between the two membranes. We show here that these two phages use different mechanisms of transmission of this stimulation signal. In the case of T4, but not of T5, a specific requirement for envelope-bound calcium was found. Indeed, addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid prevented the membrane potential changes induced by T4. This envelope-bound calcium became accessible to the chelator only as a consequence of phage adsorption and remained in this state during the depolarization and repolarization. Membrane potential changes again occurred if calcium was added after the addition of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and phage. The same concentration (300 microM) of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid prevented the T4-induced depolarization between multiplicities of infection of 6 and 30. This suggests that phage adsorption triggers both a conformational change of membrane components, the number of which reflects the number of stimuli (phages), and the liberation of a definite amount of calcium. This liberated calcium would, in turn, activate these modified membrane components to induce the depolarization. The fact that depolarization may be induced several times after a unique adsorption implies that these membrane components remain irreversibly modified.

Adsorption↗
PubMed1984

Requirement for a fluid host cell membrane in injection of coliphage T5 DNA.

Injection of T5 first-step-transfer DNA was prevented at 29 degrees C, after adsorption to an unsaturated fatty acid mutant grown on elaidate (phase transition at 35 degrees C). Local anesthetics, which increase membrane fluidity, did not inhibit injection above transition temperature and could even reverse the inhibition observed at 29 degrees C on elaidate cells.

Anesthetics, Local↗
PubMed1984

Analysis of the coliphage T5 DNA ejection process with free and liposome-associated TonA protein.

Outer membrane protein TonA, the receptor for coliphage T5, has been partially purified and incorporated into the phospholipid bilayer of liposomes. Adsorption of the phage to its receptor in either a free or liposome-associated form is fast and sufficient to trigger the ejection of encapsidated DNA. In both in vitro systems the exit of DNA from the phage capsid is a very slow process. Ejected DNA can partially accumulate inside the liposome aqueous compartment, but the transfer from the phage head to the liposome internal space is never complete, perhaps because the liposome volume is too small. The presence of polyamines or divalent cations (magnesium) or both in the incubation medium diminished the extent of DNA ejection, possibly by stabilizing DNA inside the head. DNA movement was slowed as the temperature was decreased from 37 to 18 degrees C. Furthermore, incubation at 4 degrees C totally prevented this DNA movement, even if a large part of the DNA had already exited the capsid.

Adsorption↗
PubMed1983

Host cell metabolic energy is not required for injection of bacteriophage T5 DNA.

The addition of various metabolic inhibitors (uncouplers, cyanide, arsenate, ionophores) separately or together (for example, arsenate and an uncoupler) or even harsher methods of energy depletion did not prevent bacteriophage T5 from injecting its first-step-transfer DNA (a DNA segment 3 micron long) into the cytoplasm of host cells. The same indifference to metabolic energy was observed if first-step-transfer DNA was decapsidated and uncoiled before injection, thus precluding any energetic help from the phage capsid or from some tension stored in DNA tightly packed in the head. Penetration of the second-step-transfer DNA across the cytoplasmic membrane was studied by determining injection of superinfecting T5 A2- amber phages into Sup- bacteria containing proteins A1 and A2 previously encoded by the first-step-transfer DNA of a primary wild-type phage. The addition of various metabolic inhibitors after synthesis of proteins A1 and A2 but before superinfection did not prevent this penetration of second-step-transfer DNA. Thus, we conclude that traversal of the cytoplasmic membrane by the entire T5 DNA (a molecule 34 micron long) must occur by diffusion through protein channels.

Adenosine Triphosphate↗
PubMed1981

Membrane potential changes during the first steps of coliphage infection.

Immediately after adsorption, phages T4 and T5 induce a partial depolarization of the host cytoplasmic membrane. Infected bacteria respond to this phage-induced effect by a repolarization that leads to a new steady state of reduced membrane potential. The rate and extent of repolarization are adjusted to the intensity of depolarization, which depends on the number of adsorbed phages. Consequently, the new steady state membrane potential is attained in the same interval of time regardless of the maximum depolarization. These membrane potential changes appear to be independent of phage-specific properties (type of phage, presence of DNA and internal proteins, injection process) and of several membrane-related parameters (temperature, external pH, preinfectious level of membrane potential). We propose that phage adsorption to the outer membrane triggers the emission of a signal that is transmitted to the cytoplasmic membrane. Additivity of independent signals is possible when stimuli (phages) are added at the same time. Additional adsorption of phages has no further depolarizing effect as soon as the repolarization begins. We propose that this refractoriness to secondary depolarization nd the shut-off of the first depolarization are induced by the same chemical modification also initiated by adsorption of the first phage.

Cell Membrane↗
PubMed1980

Evidence for heterogeneity in populations of T5 bacteriophage. II. Some particles are unable to inject their second-step-transfer DNA.

A new class of bacteriophage was characterized in purified T5 stocks. Regardless of the host cell, these phages were irreversibly blocked at the first-step-transfer stage under conditions in which whole DNA injection normally takes place. However, they expressed their first-step-transfer functions. These observations confirmed the previously established heterogeneity of T5 bacteriophage populations and provided a new way to define a phage function necessary to release the blocking of T5 DNA injection at the first-step-transfer stage.

Escherichia coli↗
PubMed1979

Requirement for membrane potential in injection of phage T4 DNA.

The first stages of infection by phage T4 may be divided into energy-dependent and energy-independent processes. Irreversible adsorption, unplugging, and initial exposure of the DNA terminus may occur at 4 degrees C, or at 37 degrees C in bacteria whose energy-yielding metabolism has been poisoned. DNA injection into the cytoplasm needs higher temperatures and energy from the host cell. The nature of this energy requirements was deduced from the use of metabolic inhibitors. Our results show that T4 DNA injection specifically requires the presence of a protonmotive force across the cytoplasmic membrane of the host. Moreover, the chemical gradient (delta pH) does not appear to be essential, but the membrane potential (delta psi) is required.

Biological Transport, Active↗
PubMed1974

Evidence for heterogeneity in populations of T5 bacteriophage.

Each T5 stock contains a population of particular phages that, just after adsorption onto the host bacteria. release their entire chromosome outside the bacterial membrane in a place where it is sensitive to bacterial enzymes. This release takes place before the sensitization step to deprivation of calcium and before the transfer of the first-step DNA fragment. Secondarily, this released DNA is degraded by bacterial enzymes, mainly by the endonuclease I; the products of degradation are spontaneously released in the surrounding medium. Thus, in each T5 phage stock it seems that there is a minor population that is deficient for the mechanism of controlled DNA injection into the bacteria.

Adsorption↗