Opponent: Dr. Abelardo Margolles, Dairy Research Institute of Asturias (IPLA), Spanish National Research Council (CSIC), Department Microbiology and Biochemistry of Dairy Products, Spain
Supervisor: Professor Carl Johan Franzén, Chalmers
Examiner: Professor Lisbeth Olsson, Chalmers
Many people may associate bacteria with diseases; however, bacteria are extremely important for our health, with on average 38 trillion bacterial cells naturally inhabiting the human body, mainly the gut. Among other beneficial functions, bacteria that live in and on us can provide protection against harmful bacteria and promote our immune system. The consumption of sufficient amounts of probiotic bacteria may promote our well-being in situations such as after the intake of antibiotics. Importantly, these probiotics must be alive when they are consumed.
In this thesis, the focus lies on the production of probiotic bifidobacteria. The industrial production of probiotic bifidobacteria faces many challenges. Bifidobacteria are demanding microorganisms regarding nutrient requirements. Moreover, probiotic bifidobacteria are exposed to various stressors during the production process and subsequent storage, which can impact their survival and the delivery of alive bacteria in the probiotic product. The ability to cope with and overcome these perturbations (= robustness), as well as the ability to survive storage conditions (= stability) varies among Bifidobacterium strains, although, the reason for this is poorly understood.
To improve our understanding of the properties that determine robustness and stability in bifidobacteria, I studied two commercial Bifidobacterium strains that differed with respect to these traits. For this purpose, I combined computational and experimental analyses. This allowed me to identify the nutritional requirements of the strains and to formulate a medium with defined composition, which can be used for their industrial cultivation. Moreover, I applied the newly-formulated medium for a comprehensive comparison of the two strains which revealed considerable differences in their metabolism and physiology. I also investigated the effect of changing the medium’s composition on the cellular characteristics of the two strains, including their robustness and stability. Finally, I extended my scope to more than 150 Bifidobacterium strains and looked for correlations between their genetic information and their capability to cope with stressors.
Overall, the results presented in this thesis contribute to a better understanding of the variety in robustness and stability characterizing bifidobacteria, and are expected to provide guidance for the optimization of industrial production processes relating to probiotic bifidobacteria.
KB, lecture hall, Kemigården 4, Kemi & via Zoom
07 October, 2022, 13:00
07 October, 2022, 16:00