Identification of Biofilm-Associated Cluster (bac) in Pseudomonas aeruginosa Involved in Biofilm Formation and Virulence

Biofilms are prevalent in diseases caused by Pseudomonas aeruginosa, an opportunistic and nosocomial pathogen. By a proteomic approach, we previously identified a hypothetical protein of P. aeruginosa (coded by the gene pA3731) that was accumulated by biofilm cells. We report here that a ΔpA3731 mutant is highly biofilm-defective as compared with the wild-type strain. Using a mouse model of lung infection, we show that the mutation also induces a defect in bacterial growth during the acute phase of infection and an attenuation of the virulence. The pA3731 gene is found to control positively the ability to swarm and to produce extracellular rhamnolipids, and belongs to a cluster of 4 genes (pA3729–pA3732) not previously described in P. aeruginosa. Though the protein PA3731 has a predicted secondary structure similar to that of the Phage Shock Protein, some obvious differences are observed compared to already described psp systems, e.g., this unknown cluster is monocistronic and no homology is found between the other proteins constituting this locus and psp proteins. As E. coli PspA, the amount of the protein PA3731 is enlarged by an osmotic shock, however, not affected by a heat shock. We consequently named this locus bac for biofilm-associated cluster

Immobilisation de cellules microbiennes dans des gels de pectate extrait de la pulpe de betterave (application à la biosorption du cadmium)

Ce manuscrit présente les résultats d'une étude portant sur la biosorption du cadmium par des systèmes biocatalytiques (" cellules immobilisées ") à base de pectate de betterave. Il débute par un rappel rapide des différentes techniques applicables au traitement des eaux contaminées par des métaux lourds. La caractérisation macromoléculaire des différents polysaccharides employés (alginate algaire, pectine de citrus et pectine de betterave) est ensuite présentée. Le chapitre suivant s'intéresse plus particulièrement aux propriétés mécaniques des hydrogels (chargés ou non avec des cellules). Les deux derniers chapitres sont consacrés à l'étude de la fixation du cadmium par ces mêmes hydrogels, étude réalisée tout d'abord en conditions discontinues (batch), puis en continu (bioréacteur de type colonne). Dans tous ces travaux, les résultats obtenus avec l'alginate servent de référence et sont comparés à ceux obtenus avec la pectine de betterave.Cadmium biosorption using biocatalytic systems ("immobilized cells") based on sugar beet pectin has been investigated. The manuscript begins by introducing briefly the different techniques adapted to the treatment of waters contaminated with heavy metals. The second part presents the results of the macromolecular characterization of the tested polysaccharides (algal alginate, citrus pectin and sugar beet pectin). Then, the mechanical properties of cell-free or cell-loaded hydrogels are investigated. The two last parts focus on the performance of cadmium (in dilute aqueous solutions) binding by those hydrogels, first in batch, then in continuous (column bioreactor) conditions. In all this study, results obtained with algal alginate are used as a reference data and compared to those obtained with sugar beet pectin.ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Production d'alginate par Azotobacter vinelandii dans deux types de bioréacteurs à membrane, caractérisation macromoléculaire du polysaccharide produit

Nous avons étudié la production d'alginate par A. vinelandii dans deux types de bioréacteurs à membrane (BRM). La membrane doit permettre l'extraction du milieu contenant l'alginate et la rétention des cellules. Tout d'abord, les cellules ont été immobilisées dans une structure composite gel d'agar/membrane microporeuse. Différentes membranes (tailles de pores variables) ont été utilisées. Le rendement moyen obtenu est de 0,24 g alg/g saccharose (cultures cellules libres : 0,09g/g). Il n'existe pas de relation évidente entre la taille de pore utilisée et la masse molaire (Mw) de l'alginate produit. Ce système d'immobilisation a permis de stabiliser la distribution des Mw. Nous avons ensuite utilisé un autre BRM pour la production d'alginate. Ce BRM combine un fermenteur classique (incubation continu) avec un module de microfiltration. Le rendement obtenu (0,21g/g) est similaire à celui obtenu en immobilisé. Mw diminue et la polydispersité de l'alginate augmente durant l'incubationProduction of bacterial alginate from sucrose fermentation of Azotobacter vinelandii NCIMB 9068 was performed using two different membrane bioreactors. First, viable cells were immobilized in composite agar layer/microporous membrane structures and tested for alginate production during batch incubation. Membranes with varying pore sizes (PS) were tested. The average production yield was 0,24 g alg/g sucrose (free-cell cultures : 0,09g/g). There was no evident relationship between the membrane PS and the average molecular weight (Mw) of alginate. Immobilization stabilized the Mw distribution. Second, alginate production by A. vinelandii was investigated in a membrane bioreactor which combined a continuous fermentor and a crossflow microfiltration module.The production yield (0,21 g/g) was higher than in batch process and similar to that obtained using the immobilized-cell system. A decrease in alginate Mw and an increase in polydispersity were observed as incubation proceeded.ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Immobilized viable microbial cells: from the process to the proteome… or the cart before the horse

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Electrochemical classification of antibacterial effects of betalactam antibiotics on Escherichia coli cultures

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Cellulose-based virus-retentive filters: a review

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Do β -lactam antibiotics permeabilize the outer membrane of gram-negative bacteria? An electrochemical investigation

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Susceptibility of agar-entrapped Escherichia coli cultures to cefotaxime as assessed by the potentiometric measurement of lipoic acid reduction.

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Fermentation of D-xylose by free and immobilized Saccharomyces cerevisiae

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