Physiological and molecular mechanisms involved in the survival of Fragilariopsis cylindrus (polar diatom) to prolonged darkness

• Main Author: Sciandra, Théo
• Other Authors: Institut de biologie de l'ENS Paris (IBENS), Département de Biologie - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay, Université Laval (Québec, Canada), Chris Bowler, Marcel Babin
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: Polar diatom; Prolonged darkness; Survival; Flow cytometry; Carbon reserves; Metabolism; Diatomée polaire; Obscurité prolongée; Survie; Cytométrie en flux; Réserves de carbone; Métabolisme; [SDV.BBM.BC]Life Sciences [q-bio]/Biochemistry; Molecular Biology/Biochemistry [q-bio.BM]; [SDV.BBM.BM]Life Sciences [q-bio]/Biochemistry; Molecular Biology/Molecular biology; Antarc*; Antarctic; Arctic; polar night
• Online Access: https://theses.hal.science/tel-03847766; https://theses.hal.science/tel-03847766/document; https://theses.hal.science/tel-03847766/file/98862_SCIANDRA_2022_archivage.pdf

The polar regions are characterized by extreme environmental conditions whose variations challenge the acclimation capabilities of marine sessile and planktonic organisms. One of the major challenges faced by autotrophic organisms is to survive in darkness during the long winter months. In the spring, the surviving microalgae (mostly unicellular eukaryotes) form large blooms that support the rest of the food web for summer production. Diatoms, particularly well adapted to turbulent nutrient-rich oceanic zones, dominate primary production at the poles. They are often the first to initiate spring blooms, illustrating their extraordinary ability to survive the polar night, but also to resume growth after a very long period of inactivity. Although studied many times in the past, most of the processes involved in survival remain poorly understood.The Green Life in the Dark project, in which this thesis was carried out, aims at elucidating the physiological and genetic mechanisms involved in the survival of diatoms during and just after the polar night. To do so, cultures of Fragilariopsis cylindrus (polar pennate diatom) were subjected in the laboratory to four periods of darkness lasting from one to five months, each followed by a period of re-illumination. F. cylindrus often dominates bloom production in the Arctic and Antarctic. It can also grow attached under the ice and in the water column, making it a relevant representative of polar diatoms. Its genome has also been published.We first set out to test the value of using flow cytometry in the study of survival. This technique allowed us to follow the variations of different physiological parameters of the cultures at the single-cell level, a first in this field of research. The results illustrated the imperatoris, matreque Galla.importance of considering the potential inter-individual variations occurring within a population of cells during a long acclimation to darkness. After several weeks in the dark, two subpopulations derived from the initial population ...