Biomedical subjects

Laurent Beney

Publications and source records attributed to Laurent Beney.

8 recordsLinked to original sources

PubMed2006

Membrane physical state as key parameter for the resistance of the gram-negative Bradyrhizobium japonicum to hyperosmotic treatments.

The survival of Bradyrhizobium japonicum under hyperosmotic treatments achieved at various temperatures was investigated. The bacterial viability was measured at a combination of different levels of osmotic pressure (1.4-49.2 MPa) in glycerol solutions and temperature (4-28 degrees C). Viability was dependent on these two variables, with low temperatures (10 and 4 degrees C) exhibiting a protective effect against exposure to high levels of osmotic pressure. To understand these results, the relation between membrane physical state and structure of whole cells and osmotic shock tolerance of B. japonicum was studied. Membrane physical changes were evaluated by using 1,3-diphenyl-1,3,5-hexatriene (DPH) and Laurdan (6-dodecanoil-2-dimethylaminonaphtelene) as probes. The results showed that the membrane of B. japonicum was subjected to a progressive phase transition from the liquid-crystalline to the gel phase during cooling between 28 and 4 degrees C. Accordingly, under isotonic conditions, the Laurdan GP spectra showed that, in the range 12-28 degrees C, membrane lipids were in the liquid-crystalline phase, and in a gel phase at 4 degrees C. The study of the variation in anisotropy of DPH revealed that cooling cells before the hyperosmotic treatment could induce opposite effects to the fluidizing effect of the hyperosmotic shock. Cell resistance was finally related to modifications of the membrane structure depending on combined effects of cooling and dehydration.

2-Naphthylamine↗

PubMed2005

A small HSP, Lo18, interacts with the cell membrane and modulates lipid physical state under heat shock conditions in a lactic acid bacterium.

The small heat shock proteins (sHSP) are characterized by a chaperone activity to prevent irreversible protein denaturation. This study deals with the sHSP Lo18 induced by multiple stresses in Oenococcus oeni, a lactic acid bacterium. Using in situ immunocytochemistry and cellular fractionation experiments, we demonstrated the association of Lo18 with the membrane in O. oeni cells submitted to heat shock. The same result was obtained after exposure of cells to ethanol or benzyl alcohol, agents known to have an influence on membranes. For the different stresses, the protein was located on the periphery of the cell at membrane level and was also found within the cytoplasm. In order to determine if Lo18 could interact with the phospholipids, we used model membranes made of lipids extracted from O. oeni cells. Using fluorescence anisotropy of diphenylhexatriene (DPH) and generalized polarization of Laurdan, we showed that purified Lo18 interacts with these liposomes, and increases the molecular order of the lipid bilayer in these membranes when the temperature reaches 33.8 degrees C. All these data suggest that Lo18 could be involved in an adaptive response allowing the maintenance of membrane integrity during stress conditions in O. oeni cells.

Cell Membrane↗

PubMed2005

Compared tolerance to osmotic stress in various microorganisms: towards a survival prediction test.

The osmotic tolerance of microbial cells of different microorganisms was investigated as a function of glycerol concentration and temperatures. Cells displayed specific sensitivity to dehydration in glycerol solutions. The viability of Gram-negative strains (Escherichia coli, Bradyrhizobium japonicum), Gram-positive strains (Lactobacillus plantarum, L. bulgaricus), and yeasts (Saccharomyces cerevisiae, Candida utilis) decreased with increasing osmotic pressure. For each strain, a characteristic osmotic pressure threshold causing a loss of 40% of the population at the growth temperature was determined: 26-40 MPa for E. coli, 15-25 MPa for B. japonicum, 7-15 MPa for L. bulgaricus, 40-133 MPa for L. plantarum, 50-100 MPa for S. cerevisiae, and 15-26 MPa for C. utilis. Because this threshold varies with temperature, it was possible to construct a diagram that could be helpful to the determination of the sensitivity of each strain to osmotic stress as a function of osmotic pressure and temperature.

Gram-Negative Bacteria↗

PubMed2005

Phase transitions as a function of osmotic pressure in Saccharomyces cerevisiae whole cells, membrane extracts and phospholipid mixtures.

Fourier Transform Infrared spectroscopy (FTIR) was used to determine the phase transition temperature of whole Saccharomyces cerevisiae W303-1 A cells as a function of Aw in binary water-glycerol media. A phase transition occurred at 12 degrees C in water, at 16.5 degrees C at Aw=0.75, and at 19.5 degrees C at Aw=0.65. The temperature ranges over which transition occurred increased with decreasing Aw. A total lipid extract of the plasma membranes isolated from S. cerevisiae cells was also studied, with a phase transition temperature determined at 20 degrees C in pure water and at 27 degrees C in binary water-glycerol solutions for both Aw levels tested. The pure phospholipids dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) and three binary mixtures of these phospholipids (percentage molar mixtures of DMPC/DMPE of 90.5/9.5, 74.8/25.2, and 39.7/60.3) were studied. For DMPC, there was no influence of Aw on the phase transition temperature (always 23 degrees C). On the other hand, the phase transition temperature of DMPE increased with decreasing Aw for the three aqueous solutions tested (glycerol, sorbitol and sucrose), from 48 degrees C in water, to 64 degrees C for a solution at Aw=0.67. For the DMPC/DMPE mixtures, transitions were found intermediate between those of the two phospholipids, and a cooperative state was observed between species at the gel and at the fluid phases.

Cell Membrane↗

PubMed2004

New drying process for lactic bacteria based on their dehydration behavior in liquid medium.

This study describes the different stages of optimization in an original drying process for lactic acid bacteria that allows the retrieval of dried samples of Lactobacillus plantarum with maximum viability. The process involves the addition of casein powder to bacterial pellets, followed by mixing and then air-drying in a fluidized bed dryer. The effects on bacterial viability of the a(w) of the casein powder and the kinetics of a(w) variation in the fluidized bed dryer are considered. These parameters were first studied in a water-glycerol solution and the results were then applied to the drying process. Data from the study in liquid medium were reliable in the fluidized drying stage, insofar as optimal viability was achieved for similar dehydration times (16-50 min in liquid medium, and 30 min in the fluidized bed dryer). However, when the powder was mixed rapidly with bacteria, the level of destruction differed from that observed in liquid medium. Viability was up to 70% when the a(w) of water-glycerol was 0.55, whereas it was only 2.1% when the a(w) of the casein-bacterial mix was 0.64. The predictive capacity of dehydration in liquid medium is discussed with regard to the permeability of cells to external solutes. The new process allowed 100% survival of L. plantarum after complete drying (final a(w) < 0.2). However, when used for the desiccation of L. bulgaricus, these parameters achieved a viability of less than 10%.

Dehydration↗

PubMed2003

Magnitude and kinetics of rehydration influence the viability of dehydrated E. coli K-12.

The influence of rehydration conditions on the recovery of Escherichia coli K-12 was studied. The results showed that the osmotic pressure gradient of rehydration shock realized before plating greatly affected cell viability. When rehydration occurred quickly from an hyperosmotic level of 133 MPa in glycerol solution before slow rehydration by plating on an agar surface to reach initial osmotic pressure (1.4 MPa), bacterial viability was strongly related to the intensity of the hypo-osmotic gradient used. Rehydration to 107 MPa resulted in a survival ratio of 41%, whereas strong rehydration to 1.4 MPa resulted in only 0.7% survival. These studies also demonstrated the influence of the rehydration kinetic on cell recovery. An optimal rehydration rate of 0.136 MPa x s(-1) increased cell recovery by a factor of 40 when compared with the faster and slower rates of 131.6 MPa x s(-1) and 0.006 MPa x s(-1), respectively.

Adaptation, Physiological↗

PubMed2003

Interaction of an odorant lactone with model phospholipid bilayers and its strong fluidizing action in yeast membrane.

Some odorant lactones are naturally present in fruits or in fermented products; they can also be used as food additives and can be produced by microorganisms at the industrial scale by biotechnological processes. Gamma-decalactone was previously shown to have antimicrobial properties. We determined by infrared spectroscopy measurements that this compound rapidly diffused into model phospholipid bilayers (within 2 min), modifying the general physical state of a dimyristoyl-L-alpha-phosphatidylcholine (DMPC) film. In vivo, the lactone strongly increased membrane fluidity in the model yeast Yarrowia lipolytica, as evaluated by fluorescence anisotropy measurements. This effect was more important than that of benzyl alcohol, which is known as a fluidizing agent in living cells, and may explain the toxic action of gamma-decalactone in microorganisms.

Anti-Bacterial Agents↗

PubMed2002

Viability of Escherichia coli after combined osmotic and thermal treatment: a plasma membrane implication.

This study investigates the influence of temperature (T) and osmotic pressure (Pi) on the viability of Escherichia coli K12 during an osmotic treatment. Osmotic shock (dehydration and rehydration within 1 s) in liquid media at different temperatures (4, 10, 30 and 37 degrees C) and different levels of osmotic pressure (26, 30, 35, 40, 82 and 133 MPa) were realized. Results show that a sudden dehydration, below 40 MPa, destroyed up to 80% of the bacterial population for each tested temperature, whereas viability was greater than 90% for an osmotic pressure less than 26 MPa. The influence of T and Pi on the membrane's physical structure is finally considered to explain the results in light of FTIR and electron microscopy study of the influence of temperature and osmotic pressure on E. coli membrane phospholipids conformation.

Cell Membrane↗