Trophic relationships between Saccharomyces cerevisiae and Lactobacillus plantarum and their metabolism of glucose and citrate

Glucose and citrate are two major carbon sources in fruits or fruit juices such as orange juice. Their metabolism and the microorganisms involved in their degradation were studied by inoculating with an aliquot of fermented orange juice a synthetic model medium containing glucose and citrate. At pH 3.6, their degradation led, first, to the formation of ethanol due to the activity of yeasts fermenting glucose and, eventually, to the formation of acetate resulting from the activity of lactobacilli. The yeast population always outcompeted the lactobacilli even when the fermented orange juice used as inoculum was mixed with fermented beet leaves containing a wider variety of lactic acid bacteria. The evolution of the medium remained similar between pH 3.3 and 5.0. At pH 3.0 or below, the fermentation of citrate was totally inhibited. Saccharomyces cerevisiae and Lactobacillus plantarum were identified as the only dominant microorganisms. The evolution of the model medium with the complex microbial community was successfully reconstituted with a defined coculture of S. cerevisiae and L. plantarum. The study of the fermentation of the defined model medium with a reconstituted microbial community allows us to better understand the behavior not only of fermented orange juice but also of many other fruit fermentations utilized for the production of alcoholic beverages

Dynamics and structure of decaying shallow dipolar vortices

The current work reports on a numerical and experimental study of the evolution of decaying dipolar vortices in a shallow fluid layer. The dynamics and the structure of such vortices are investigated as a function of both their Reynolds number Re and the aspect ratio of vertical and horizontal length scales δ. By quantifying the strength of the secondary motions (vertical motions and nonzero horizontal divergence) with respect to the swirling motions of the primary vortex cores, it was found that the three-dimensionality of a shallow (δ << 1) dipolar vortex only depends on a single parameter: δ²Re. Depending on the value of this parameter, three flow regimes are observed for shallow dipolar vortices: (1) a quasi-two-dimensional regime where the structure of the dipolar vortex remains almost unchanged throughout its lifetime, (2) a transitional regime where the structure presents some three-dimensional characteristics but remains coherent, and (3) a three-dimensional regime where the structure of the dipolar vortex acquires a complicated three-dimensional shape with a persistent spanwise vortex at its front

Quelques données récentes sur la biologie des écosystèmes méthanogènes

La production biologique de méthane est actuellement décrite par schéma en trois étapes. Deux d'entre elles restent mal connues : la méthanogenèse à partir de l'acétate et surtout l'acétogenèse avec production obligée d'hydrogène. Pourtant elle sont souvent les étapes limitant la vitesse globale de la méthanisation. Après une revue des acquis récents, des espèces impliquées et de leurs interactions au sein écosystèmes méthanogènes, nous discutons l'application de ces concepts à la biologie des fosses septiques

Ecophysiologie des boues activées induites dans les stations d'épuration industrielles ou mixtes par les effluents à forte charge glucidique

Des boues activées traitant des effluents riches en glucides (ceux des industries agro-alimentaires en particulier) sont prédisposées aux accidents de décantation de type foisonnement des boues ou « bulking filamenteux ». Après un rappel bibliographique de l'écologie et de la physiologie des germes présents dans les boues activées adaptées à des effluents riches en glucides, nous présentons les mécanismes probables d'implantation du bulking filamenteux pour ce type particulier de boues activées. Les travaux réalisés dans notre laboratoire montrent que la prolifération préférentielle des espèces filamenteuses est à relier au métabolisme des réserves endocellulaires synthétisées par deux types de microorganismes lorsque l'oxygène ou l'azote sont des facteurs limitants (a-glucanes chez les espèces non filamenteuses, P.H.B. chez les espèces filamenteuses). Dans la dernière partie de notre exposé, nous discutons les modifications qu'il convient d'apporter au procédé par boues activées classique pour traiter avec succès ce type d'effluent (supplémentation de l'eau résiduaire, compartimentage du bassin d'alimentation, utilisation du procédé « contact - stabilisation » à forte charge)

Homoacetogenic Fermentation of Cellulose by a Coculture of Clostridium thermocellum and Acetogenium kivui

Interrelationships between methanogens and fermentative or hydrolytic bacteria are well documented; however, such cocultures do not allow a complete fermentation shift to a peculiar metabolite. We describe here a new stable association between Clostridium thermocellum and Acetogenium kivui which converts 1 mol of cellulose (anhydroglucose equivalent) into 2.7 mol of acetate

Citrate Metabolism By Lactobacillus-plantarum Isolated From Orange Juice

The behaviour of strains of Lactobacillus plantarum isolated from fermented orange juice and Lact. plantarum DSM 20174 was studied in the presence of citrate. When used as sole carbon source, citrate scarcely supported the growth of the bacteria. It was shown to enhance the growth of Lact. plantarum in glucose media. Under acid conditions (pH 4.0-5.0), 1 mol of citrate yielded 1.7 mol of acetate as sole major final metabolite with release of CO2 in the gas phase

Interactions entre espèces microbiennes anaérobies dans le rumen

International audienc

Isolation and characterization of a thermophilic Methanobacterium able to use formate, the strain FTF

International audienceA thermophilic anaerobic which produced methane from formate and H2 and CO2 was isolated from a bench-scale digester treating a mixture of solid wastes at 55°C, after enrichment cultures on sodium acetate. The cells were slightly crooked rods occurring singly or in filaments. The bacterium was not motile, and stained Gram positive. Colonies appearing after 1 week of incubation were white with filamentous edges and 1 mm in diameter. The organism used H2:CO2 or formate as an energy source. Yeast extract was not required but stimulated growth significantly. Casamino acids were stimulatory and could serve as a nitrogen source. Cysteine was used as a sulfur source. The optimum pH for growth was 7.5. Growth occurred from 35 to 70°C with an optimum at 55°C. The deoxyribonucleic acid base composition was 49.2 mol% guanine plus cytosine. Though this isolate conforms to Methanobacterium thermoformicium, its proper assignment awaits further studies. It has been deposited in the Deutsche Sammlung von Mikroorganismen as strain DSM 3012

Clostridium neopropionicum sp. nov., a strict anaerobic bacterium fermenting ethanol to propionate through acrylate pathway

International audienceStrain X4 was isolated several years ago from an anaerobic mesophilic plant treating vegetable cannery waste waters. It was the first example of propionic fermentation from ethanol. Morphologic and physiologic characterizations of the strain are presented here. This strain is described as type strain of a new species, Clostridium neopropionicum sp. nov. Whole cells of strain X4 ferment [1-13C]ethanol and CO2 to [2-13C]propionate, [1-13C]acetate and [2-13C]propanol, suggesting the absence of a randomizing pathway during the propionate formation. Enzymes involved in this fermentation were assayed in cell-free extracts of cells grown with ethanol as sole substrate. Alcohol dehydrogenase, aldehyde dehydrogenase, phosphate acetyl transferase, acetate kinase, pyruvate synthase, lactate dehydrogenases, and the enzymes of the acrylate pathway were detected at activities sufficient to be involved in ethanol fermentation. The same pathway may be used for the degradation of lactate or acrylate to acetate