Florencio Bellido, Francisco JavierDíaz Troya, Sandra2025-06-062025-06-062025-02-11Ortega Martínez, P. (2025). The role of glycogen Metabolism in the Adaptation to environmental Changes of the cyanobacterium Synechocystis sp. PCC 6803. (Tesis Doctoral Inédita). Universidad de Sevilla, Sevilla.https://hdl.handle.net/11441/174010Glycogen is the primary polysaccharide in cyanobacteria, serving as a critical carbon and energy reservoir to support cellular energy homeostasis. Its metabolism is conserved, requiring only a few steps from glucose-6P to incorporate glucose molecules into glycogen chains. This study investigates the role of key enzymes in glycogen metabolism and how these reserves help Synechocystis sp. PCC 6803 adapt to environmental changes, enhancing the resilience of this model photosynthetic organism. By examining phosphohexomutases, that interchange the phosphate of glucoses, the work identifies the sll0726 as the main phosphoglucomutase. Cellular fitness is compromised under conditions that demand higher flux towards glycogen synthesis, such as high light, nitrogen depletion (chlorosis). This work expands our understanding of how to regulate carbon flow towards desired compounds by diverting it from glycogen reserves. The research also focuses on the importance of glycogen in the transition from phototrophic to photomixotrophic growth. Glucose supplementation induces metabolic adaptations and glycogen accumulation, with limited glycogen synthesis proving detrimental to photomixotrophic growth, causing significant metabolic and photosynthetic disruptions. Moreover, the work explores how nitrogen depletion and photomixotrophic lethality in glycogen-deficient strains reveal the crucial role of chlorosis regulation. This adaptative program requires an active photosynthetic electron transport chain, ensuring reduced PSI. Glucose addition to WT strain during nitrogen deprivation prevents chlorosis, impairing photosynthesis. Finally, this study uncovers potential alternative pathways for polysaccharide synthesis beyond the canonical glycogen synthases. Overall, this work emphasizes the diversity of cyanobacterial metabolism, showcasing its metabolic plasticity and underscores the need to further explore the metabolic functions of photosynthetic prokaryotes.application/pdf238 p.engAttribution-NonCommercial-ShareAlike 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-sa/4.0/info:eu-repo/semantics/doctoralThesisinfo:eu-repo/semantics/openAccess