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Transcriptomic study of the yeast Yarrowia lipolytica metabolism in a cheese ecosystem

Soulaf Mansour
Abstract : The adaptation of microorganisms to their environment depends on both their ability to cope with the physico-chemical characteristics of the cheese and their ability to degrade substrates in their environment, while interacting with other microbial species. Controlling the dynamics of populations remains a major challenge in order to control the different steps of cheese production. The flora being selected, this could enable, to shorten the ripening time significantly while maintaining or even improving the microbial and organoleptic qualities of the cheese. Many studies have highlighted the inability of adaptation of the inoculated microorganisms, which are in competition with the natural flora of the cheese. The objective of this work was to better understand the adaptative metabolism of the ubiquitous yeast Yarrowia lipolytica. As a first step, we chose to study the metabolism of this yeast in mono-culture focusing on key metabolic pathways of cheese ripening, lactate and amino acids catabolism. The combination of molecular, microbiological, biochemical and proteomics techniques has helped to confirm a real preference of this yeast for amino acids. The lack of amino acids induces an oxidative stress in Y. lipolytica. Moreover, a correlation between the consumption of amino acids and the production/accumulation of ammonia by the yeast has been highlighted. Ammonia could have a role i) in the alcalinisation of the medium, an essential step in the manufacture of cheese for the development of the acid-sensitive flora ii) as a signal molecule between yeasts. In a second step, the study of the interaction in yeast with 2 bacteria was performed: Lactococcus lactis and Staphylococcus xylosus. A first step was to understand the phenomena of interaction in a chemically defined medium, using a targeted approach (quantitative RT-PCR) on genes involved in the catabolism of lactate, pyruvate or amino acids. The mixed culture study allows the identification of interactions phenomena between micro-organisms in terms of growth or metabolic complementarity. Indeed, in the presence of S. xylosus major genes involved in the amino acids catabolism are repressed in the yeast. In addition, the expression of Y. lipolytica lactate dehydrogenase is induced by the production of lactate by both bacteria. In a second step, the study of yeast co-culture was conducted in a model cheese matrix called
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Submitted on : Thursday, September 10, 2009 - 8:00:00 AM
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Soulaf Mansour. Transcriptomic study of the yeast Yarrowia lipolytica metabolism in a cheese ecosystem. Life Sciences [q-bio]. AgroParisTech, 2009. English. ⟨NNT : 2009AGPT0035⟩. ⟨pastel-00005341⟩

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