Effect of double stress - cold and acid on the degradation of physiological membrane's state of Bifidobacterium animalis subsp. lactis and its relation with the content of conjugated linoleic acid in organic milk
The aims of this project are to understand the mechanisms of degradation of the physiological state of Bifidobacterium animalis subsp. lactis when exposed to double stress: cold and acid related to the levels of conjugated linoleic acid (CLA) of milk, to improve the stability during deleterious conditions. First, it will be study the growth of B. animalis subsp. lactis with other lactic acid bacterias in organic milk, and its resistance to double stress - cold and acid during their survival. This will also allow identifying the physiological mechanisms leading to cell damage after the double stress. The results of the stress will be studied both in the membrane (levels of saturated fatty acids, unsaturated fatty acids and cyclic fatty acids will be measured), and in the cytoplasm (two-dimensional electrophoresis analysis of proteomic and cell proteins related to the stress will be carried out). Because of the importance of fatty acids to the membrane's responses to bacterial stress, it is suitable to study the effects of CLA contents, both on the Bifidobacterium sp growth, but also about its survival to cold and acid. The study of the influence of different levels of CLA in the fatty acid composition of the membrane of B. animalis subsp. lactis will allow understanding the phenomenon, and its association with the sensitivity to stress. In addition, this research will attempt to verify the potential of Bifidobacterium sp to increase the contents of CLA when some substrates are added to organic milk. Finally, this work seeks to establish physiological adaptations of cells in the membrane and proteomics levels in order to allow the cells a better resistance to damaging conditions of stress, and thereby obtain higher bacterial counts and more stability. These adjustments will be related through the creation of conditions of moderate stress (pH and temperature) to the content of CLA in milk, allowing modifications of the bacteria's membrane composition in terms of fatty acids and proteomics before being submitted to real double stress. The originality of this project is to share the knowledge of São Paulo University, Brazil, especially involving probiotic fermentation of organic milk and the UMR Génie Microbiologie des Procedes Alimentaires, AgroParisTech, France on the physiological characterization of lactic acid bacteria and the application of the adaptations. This work will enhance the knowledge of probiotic fermentation by improving its control and quality for applications in human and animal health.
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