Mutations in Sugar-Nucleotide Synthesis Genes Restore Holdfast Polysaccharide Anchoring to Caulobacter crescentus Holdfast Anchor Mutants

Attachment is essential for microorganisms to establish interactions with both biotic and abiotic surfaces. Stable attachment of Caulobacter crescentus to surfaces requires an adhesive polysaccharide holdfast, but the exact composition of the holdfast is unknown. The holdfast is anchored to the cell envelope by outer membrane proteins HfaA, HfaB, and HfaD. Holdfast anchor gene mutations result in holdfast shedding and reduced cell adherence. Translocation of HfaA and HfaD to the cell surface requires HfaB. The Wzx homolog HfsF is predicted to be a bacterial polysaccharide flippase. An hfsF deletion significantly reduced the amount of holdfast produced per cell and slightly reduced adherence. A ΔhfsF ΔhfaD double mutant was completely deficient in adherence. A suppressor screen that restored adhesion in the ΔhfsF ΔhfaD mutant identified mutations in three genes: wbqV, rfbB, and rmlA. Both WbqV and RfbB belong to a family of nucleoside-diphosphate epimerases, and RmlA has similarity to nucleotidyltransferases. The loss of wbqV or rfbB in the ΔhfsF ΔhfaD mutant reduced holdfast shedding but did not restore holdfast synthesis to parental levels. Loss of wbqV or rfbB did not restore adherence to a ΔhfsF mutant but did restore adherence and holdfast anchoring to a ΔhfaD mutant, confirming that suppression occurs through restoration of holdfast anchoring. The adherence and holdfast anchoring of a ΔhfaA ΔhfaD mutant could be restored by wbqV or rfbB mutation, but such mutations could not suppress these phenotypes in the ΔhfaB mutant. We hypothesize that HfaB plays an additional role in holdfast anchoring or helps to translocate an unknown factor that is important for holdfast anchoring

Aroma compound transfer between a solid food matrix and packaging films: a comprehensive approach

International audienceFood quality is highly dependent on mass transfers occurring in food / packaging systems during storage. Particularly, aroma compound transfers are influenced by the composition and structure of the packaging and food matrix, the physico-chemical properties of aroma compounds and the conditions of the external environment (1). The influence of the food matrix on aroma compound-packaging film interactions was little studied in the literature (2,3). The objective of this work, in the framework of the French project CANAL ARLE, is to better understand aroma compound transfer into and through cellulosic and thermoplastic packaging films by taking into account their interaction with a sponge cake during storage in controlled conditions. The sponge cake is flavoured either with a complex aromatic note (ppb - ppm range) or with some tracers of this formula (500 ppm for each aroma compound)

A new approach to studying sponge cake aroma after storage in treated paper and plastic packaging by direct gas chromatography-olfactometry (D-GC-O)

International audienceThe objective of this study was to use D-GC-O to compare the global odour of a sponge cake flavoured with either a viennoiserie aromatic note or a simplified mixture of aroma compounds (used for physicochemical studies), then stored in a glass packaging (inert and impermeable) or in pouches made with treated papers or with plastic packaging, in accelerated ageing conditions (high temperature and relative humidity gradient). After 1 week of storage, the flavoured sponge cake headspace was SPME-extracted directly into the packaging and analysed by D-GC-O. The sponge cake global odour was better retained if plastic film rather than treated-papers was used, for both flavourings. Changes in the relative proportions of aroma compounds in the sponge cake during storage modified the perceived global odour. This was due to their modified retention in the sponge cake and to their transfer through the packaging. SPME coupled to D-GC-O was confirmed to be a rapid and sensitive method for comparing the aroma compound barrier properties of various packaging films with flavouring mixtures at concentrations close to reality

Intracellular targeting of truncated secretory peptides in the mammalian heart and brain

Secretory polypeptides are vital for nervous system function, sleep, reproduction, growth, and metabolism. Ribosomes scanning the 5'-end of mRNA usually detect the first AUG site for initiating translation. The nascent propeptide chain is then directed via a signal-peptide into the endoplasmic reticulum, processed through the Golgi stacks, and packaged into secretory vesicles. By expressing prepropeptide-EGFP fusion proteins, we observed unusual destinations, mitochondria, nucleus, and cytoplasm, of neuropeptide Y (NPY), atrial natriuretic peptide, and growth hormone in living murine cardiac cells and hypothalamic slices. Subcellular expression was modulated by Zn++ or mutations of N-terminal prohormone sequences but was not due to overexpression in the trans-Golgi network. Mitochondrial targeting of NPY also occurred without the EGFP tag, was enhanced by site-directed mutagenesis of the first AUG initiation site, and abolished by mutation of the second AUG. Immunological methods indicated the presence of N-terminal truncated NPY in mitochondria. Imaging studies showed depolarization of NPY-containing mitochondria. P-SORT software correctly predicted the secondary intracellular destinations and suggested such destinations for many neuropeptides and peptide hormones known. Thus, mammalian cells may retarget secretory peptides from extracellular to intracellular sites by skipping the first translation-initiation codon and thereby alter mitochondrial function, gene expression, and secretion

Change in the aroma quality of a sponge cake during storage in flexible packaging films evalued by D-GC-O

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Thermo-hydrous behavior of hardened cement paste based on calcium aluminate cement

International audienceRefractory castables based on aluminous hydraulic binders are commonly used in aluminium casthouses (furnaces, ducts, etc.). Their selection is based on their good mechanical strength, thermal behavior and compatibility with molten aluminium. However, few studies focus on their hydrous evolution in operation, whereas this property can also have an influence on the produced metal quality. In this article, the internal moisture of twelve hardened cement pastes fired at high temperature, made with four aluminous hydraulic binders and three different Water/Binder ratios was registered under diverse thermo-hydrous conditions, including at high temperature. The water trapped by physisorption and chemisorption can be significant for some products, and it strongly depends on the mineralogy and porosity of the hardened cement paste. The more the binders contain alumina phase, the more the hardened cement pastes mobilize and render moisture

Ethyl hexanoate transfer in paper and plastic food packaging by sorption and permeation experiments

The barrier properties of one treated paper packaging and one standard plastic film (bi-oriented polypropylene, biOPP) were assessed for ethyl hexanoate. Three methods based either on sorption (gravimetry and micro-atmosphere-derived method) or permeation kinetic determination were used in controlled conditions of aroma vapor concentration (107 Pa), temperature (25 degrees C) and relative humidity (about 0 %). Ethyl hexanoate solubility values were on the same range of magnitude for both packaging films in spite of their different nature and composition. Ethyl hexanoate affinity for both films was well predicted by their respective solubility parameters. Solubility values were different according to the experimental method used. The micro-atmosphere-derived method and the permeation method both presented experimental limitations for the solubility determination. Ethyl hexanoate diffusivity values were significantly different between the three methods used. Particularly, the values were 10-folds higher by the permeation method than by the sorption methods for the treated paper. Whatever the method, ethyl hexanoate diffusivity was always higher through the treated paper than through the biOPP. Ethyl hexanoate permeability was controlled by diffusivity for both films and probably linked to the evolution of the film structure during transfer. Permeability could thus not be calculated from the product of diffusivity and solubility coefficient