Grégory Francius

Publications (36) View all

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  Available from: Grégory Francius

  Article: In vitro interactions between probiotic bacteria and milk proteins probed by atomic force microscopy.

  J Burgain, C Gaiani, G Francius, A M Revol-Junelles, C Cailliez-Grimal, S Lebeer, H L P Tytgat, J Vanderleyden, J Scher
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  ABSTRACT: Interactions between microbial cells and milk proteins are important for cell location into dairy matrices. In this study, interactions between two probiotic strains, Lactobacillus rhamnosus GG and Lactobacillus rhamnosus GR-1, and milk proteins (micellar casein, native and denatured whey proteins) were studied. The bacterial surface characterization was realized with X-ray photoelectron spectroscopy (XPS) to evaluate surface composition (in terms of proteins, polysaccharides and lipid-like compounds) and electrophoretic mobility that provide information on surface charge of both bacteria and proteins along the 3-7 pH range. In addition, atomic force microscopy (AFM) enabled the identification of specific interactions between bacteria and whey proteins, in contrast to the observed nonspecific interactions with micellar casein. These specific events appeared to be more important for the GG strain than for the GR-1 strain, showing that matrix interaction is strain-specific. Furthermore, our study highlighted that in addition to the nature of the strains, many other factors influence the bacterial interaction with dairy matrix including the nature of the proteins and the pH of the media.
  Colloids and surfaces. B, Biointerfaces 12/2012; 104C:153-162. · 2.60 Impact Factor
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  Article: Production of extracellular glycogen by Pseudomonas fluorescens: spectroscopic evidence and conformational analysis by biomolecular recognition.

  Fabienne Quilès, Pavel Polyakov, François Humbert, Grégory Francius
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  ABSTRACT: Glycogen is mainly found as the principal storage form of glucose in cells. Many bacteria are able to synthesize large amounts of glycogen under unfavorable life conditions. By combining infrared spectroscopy, single molecule force spectroscopy (SMFS) and immuno-staining technique, we evidenced that planktonic P. fluorescens (Pf) cells are also able to produce glycogen as an extracellular polymeric substance. For this purpose, Pf suspensions were examined at 3 and 21 h of growth in nutritive medium (LB, 0.5 g/L). The conformation of the extracellular glycogen, revealed through its infrared spectral signature, has been investigated by SMFS measurements using Freely Jointed Chain model. The analysis of force versus distance curves showed over growth time that the increase of glycogen production was accompanied by an increase in glycogen contour lengths and ramifications. These results demonstrated that the production of extracellular bacterial glycogen can occur even if the cells are not subjected to unfavorable life conditions.
  Biomacromolecules 06/2012; 13(7):2118-27. · 5.48 Impact Factor
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  Article: Antibacterial activity of class IIa bacteriocin Cbn BM1 depends on the physiological state of the target bacteria.

  Thibaut Jacquet, Catherine Cailliez-Grimal, Grégory Francius, Frédéric Borges, Muhammad Imran, Jérôme F L Duval, Anne-Marie Revol-Junelles
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  ABSTRACT: Carnobacteriocin BM1 (Cbn BM1) is a class IIa bacteriocin produced by Carnobacterium maltaromaticum CP5 isolated from a French mold ripened cheese. Numerous studies highlight variations in numerous parameters, such as bacterial membrane composition and potential, according to physiological changes. In this work, the mechanism of action of an oxidized form of Cbn BM1 was studied on C. maltaromaticum DSM20730 in log and stationary growth phases. Membrane integrity assessment and high resolution imaging by atomic force microscopy confirmed the link between physiological state and bacterial sensitivity to Cbn BM1. Indeed, these approaches enable visualizing morphological damage of C. maltaromaticum DSM20730 only in an active dividing state. To specifically address the interaction between peptide and bacterial membrane, fluorescence anisotropy measurements were conducted. Results revealed strong modifications in membrane fluidity by Cbn BM1 only for C. maltaromaticum DSM20730 in log growth phase. In a similar way, the Δψ component, but not the ΔpH component of the proton-motive force, was perturbed only for bacteria in log growth phase. These results clearly show that a class IIa bacteriocin antimicrobial mechanism of action can be modulated by the physiological state of its target bacteria.
  Research in Microbiology 05/2012; 163(5):323-31. · 2.76 Impact Factor
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  Article: Polyethyleneimine-mediated flocculation of Shewanella oneidensis MR-1: impacts of cell surface appendage and polymer concentration.

  Marie-Eve M Krapf, Bruno S Lartiges, Christophe Merlin, Grégory Francius, Jaafar Ghanbaja, Jérôme F L Duval
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  ABSTRACT: In wastewater treatment plants, optimizing bacterial flocculation and bacterial sludge dewatering requires a detailed understanding of the concomitant biological and physico-chemical processes governing the action of flocculating agent on living cells. Here we investigate the interactions between polyethyleneimine (PEI, 60,000g/mol) and Shewanella oneidensis MR-1 lacking or not the lipopolysaccharide (LPS) O-antigen surface structure. Flocculation tests were performed on bacteria with/without LPS O-antigen after being exposed to 0-100mg/L PEI concentrations. Measurements of electrophoretic mobility and bacterial aggregates size were complemented by transmission electron micrographs and atomic force microscopy images. While low PEI concentrations (<20mg/L) lead to flocculation of both bare and LPS O-antigen-decorated bacterial strains, the lysis of bacterial membranes occurred at larger polymer concentrations for the latter, which highlights the protective role of LPS O-antigen against harmful PEI-mediated membrane alterations. Depending on polymer concentration, two types of bacterial aggregates are identified: one that solely integrates bacterial cells, and another that includes both cells and cell residues resulting from lysis (membrane and/or LPS fragments, and inner cell content materials). The latter is expected to significantly contribute to water entrapping in sludge and thus lower dewatering process efficiency.
  Water Research 04/2012; 46(6):1838-46. · 4.86 Impact Factor
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  Article: Determination of the matrix indentation modulus of Meuse/Haute-Marne argillite

  V Magnenet, C Auvray, G Francius, A Giraud
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  ABSTRACT: Keyword: Nanoindentation Meuse/Haute-Marne argillite Statistical analysis Nanoindentation tests were carried out on Meuse/Haute-Marne argillite. The aim of this first experimental investigation was to quantify the indentation modulus of the argillaceous matrix in order to specify micromechanical models already developed for this material. We opted for an order of magnitude of inden-tation depth h which was much larger than the "small" matrix inclusions size (1 μm in size) and much smaller than "big" quartz and calcite inclusions size (between 10 μm and 50 μm) to enable the measurement of a homogeneous matrix behavior. The experimental frequencies of indentation modulus were further compared to a superposition of Gaussian probability densities in order to estimate the indentation modulus of each constituent. A two-constituent model—with the two mean values 5.2 and 23.0 GPa—was found to fit well with the experimental data.
  Applied Clay Science 03/2011; · 2.47 Impact Factor