3 research outputs found

    De l'induction de la conidiation à la qualité des conidies de Penicillium camemberti en culture de surface (une étude pluridisciplinaire)

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    La conidiation de Penicillium camemberti, un ferment d'affinage, a été étudiée en culture de surface, d'un point de vue physiologique et moléculaire. Le développement d'une technique d'inoculation par trempage de filtre a permis de travailler sur un matériel biologique homogène et de réaliser des transferts de mycélium d'un milieu à un autre. Dans ces conditions de culture, il a été démontré que le nitrate de potassium stimule la conidiation, alors que le sulfate d'ammonium l'inhibe. Le temps nécessaire à l'acquisition de la compétence a été évalué à 51 heures. Différents facteurs nutritionnels ont ensuite été testés pour déterminer leur influence, soit positive, soit négative, sur la conidiation de Penicillium camemberti. L'étude de l'effet du calcium et du rapport carbone sur azote (C/N) a alors été approfondie. D'une point de vue moléculaire, nous avons identifiés les gènes brlA et wetA, potentiellement impliqués dans le contrôle de la conidiation de Penicillium camemberti. L'analyse de l'expression du gène brlA a mis en évidence une corrélation entre le niveau d'expression de ce gène et le taux de conidiation. La qualité des conidies a été étudiée en fonction des conditions de culture, notamment liquide et solide. Le dosage du contenu des conidies en polyols et tréhalose ainsi qu'une analyse ultrastructurale nous a permis d'interpréter les différences de résistance à la lyophilisation et de capacité de couverture d'un milieu fromage.The conidiation of Penicillium camemberti, a ripening fungus, was examined on solid media from a physiological and molecular point of view. The development of a technique of inoculation by soaking filters made possible to work on a homogeneous biological material and to transfer easily mycelium from a medium to an another. Under these conditions of culture, it was shown that potassium nitrate stimulates the conidiation, whereas ammonium sulfate inhibits it. The time necessary to acquire the competence was evaluated at 51 hours. Various nutritional factors were then tested to determine their influence, either positive, or negative, on the conidiation of Penicillium camemberti. The effect of calcium and the carbon to nitrogen ratio (C/N was then thoroughly studied. From a molecular point of view, we identified the brlA and wetA genes, potentially implied in the control of the conidiation of Penicillium camemberti. The analysis of the expression of the brlA gene highlighted a correlation between the level of expression of this gene and the rate of conidiation. The quality of the conidies was studied according to the conditions of culture, in particular liquid and solid. The determination of the polyols and trehalose contents of the conidies as well as an ultrastructural analysis enabled us to interpret differences into resistance to freeze-drying and capacity of covering a cheese medium.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

    Metabolism of fatty acid in yeast: Characterisation of beta-oxidation and ultrastructural changes in the genus Sporidiobolus sp cultivated on ricinoleic acid methyl ester

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    International audienceCell structure modifications and b-oxidation induction were monitored in two strains of Sporidiobolus, Sp. Ruinenii and Sp. pararoseus after cultivation on ricinoleic acid methyl ester. Ultrastructural observations of the yeast before and after cultivation on fatty acid esters did not reveal major modifications in Sp. ruinenii. Unexpectedly, in Sp. pararoseus a proliferation of the mitochondrion was observed. After induction, Sp. ruinenii principally exhibited an increase in the activities of acyl-CoA oxidase (ACO), hydroxyacyl- CoA deshydrogenase (HAD), thiolase and catalase. In contrast, Sp. pararoseus lacked ACO and catalase activities, but an increase in acyl-CoA deshydrogenase (ACDH) and enoyl-CoA hydratase (ECH) activity was observed. These data suggest that in Sp. ruinenii, b-oxidation is preferentially localized in the microbody, whereas in Sp. pararoseus it might be localized in the mitochondria

    Impact of solid medium composition on the conidiation in Penicillium camemberti

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    International audienceConidiation of an industrial strain of Penicillium (P.) camemberti, a ripening fungus, was examined on solid media. In order to evaluate the influence of nutritional factors on conidiation, we developed an inoculation and transfer procedure that allowed to obtain an homogenous mycelial biomass. Absence of conidiation was observed when ammonium sulphate and sodium nitrate were used as nitrogen sources. In contrast, conidiation increased significantly in the presence of ammonium phosphate or potassium nitrate with 4.8 × 106 and 12 × 106 spores ml−1, respectively. By using those optimal conditions, the influence of nutrient starvation or calcium supply on conidiation was studied. Under the conditions tested, nitrogen starvation and calcium supply were better inducers than carbon starvation. A high carbon-to-nitrogen (C/N) ratio provided the highest level of with 4.2 × 107 spores ml−1 and a sporulation index of 8.2 after 16 days of cultivation
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