Percorrer por autor "Almeida, Mafalda de Carvalho"
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- Unravelling mixotrophy in dinoflagellates: connecting transcript analysis to physiological rate measurements across light intensitiesPublication . Almeida, Mafalda de Carvalho; Ferreira, Guilherme Duarte; Felício, Verónica Manuela RôxoMixotrophy, the fusion between photosynthesis and phagotrophy within a single cell, is a dominant nutritional strategy in marine plankton, conferring a significant competitive advantage in variable environments. However, the molecular mechanisms regulating the balance between these two metabolic pathways remain poorly understood. This dissertation investigated the physiological and molecular regulation of the dinoflagellate Karlodinium veneficum under three different light regimes of 7, 45, and 300 PAR.m⁻².s⁻¹ under contrasting trophic strategies, by comparing autotrophy against mixotrophy utilizing Rhodomonas salina as prey. Through an integrative approach, physiological rates (growth, ingestion, respiration, photosynthesis) were quantified, cellular energy allocation (lipids, carbohydrates, ATP) and the expression of key metabolic genes were analysed. The results revealed that a light intensity of 45 μmol PAR.m⁻².s⁻¹ represents the metabolic optimum for mixotrophy, maximizing ingestion rates and photosynthetic efficiency. Unexpectedly, autotrophic growth exceeded mixotrophic growth, suggesting energetic costs associated with predation. Nevertheless, mixotrophic cells demonstrated a higher capacity for energy reserve accumulation and superior photosynthetic rates, indicating a metabolic synergy where prey ingestion enhances the photosynthetic machinery. Connecting transcript analysis to physiological rates, the molecular data provided a mechanistic explanation for the observed metabolic strategy. The transcriptional stability of phosphoribulokinase, prk, underpinned the sustained photosynthetic rates and ATP production observed across trophic modes, confirming that the Calvin cycle operates constitutively and is not repressed by feeding. Simultaneously, the apparent downregulation of cytochrome c oxidase subunit I, cox1, under mixotrophy aligned with the physiological increase in gross oxygen production efficiency. This inverse relationship suggests that prey ingestion alleviates the respiratory burden of biosynthesis, allowing the cell to maximize photosynthetic output with reduced mitochondrial investment. This study highlights the complexity of mixotrophic regulation and underscores the importance of integrating molecular and physiological tools to understand the role of these organisms in marine ecosystem.