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Adaptations des cyanobactéries marines du genre Synechococcus au gradient latitudinal de température

Justine Pittera 1
1 MAPP - MArine Phototrophic Prokaryotes
AD2M - Adaptation et diversité en milieu marin
Abstract : Marine picocyanobacteria are the most abundant photosynthetic organisms on Earth. Among them, Synechococcus displays a wide latitudinal distribution, ranging from the equator to polar circles, suggesting that they have evolved efficient adaptive strategies to cope with the latitudinal temperature gradient. The first part of this PhD work aimed at studying the thermophysiology of different lineages of the marine Synechococcus radiation. The combination of thermal acclimation and stress experiments with a phyloecology study allowed unveiling the existence of lineages physiologically specialized in distinct thermal niches, i.e. thermotypes. This work furthermore pointed out the importance of the capacities to optimize the photosynthetic apparatus efficiency for successful temperature acclimation. The thermostability of photosystem II, a key complex to the regulation of light energy utilisation, was compared within several marine Synechococcus strains. The results revealed that the photosynthetic antenna and its components have distinct thermostabilities, which are related to the strain isolation latitude. Structural homology models of phycobiliproteins thus revealed sites of molecular adaptation of the antenna to temperature. The function of the photosynthetic complexes is dependent on the fluidity of the membranes in which they are embedded, a physical factor regulated by temperature. The results a first lipidomic study suggested that the regulation of the composition in acyl chains plays an important role in temperature acclimation in marine Synechococcus. Furthermore, genomic comparative analyses revealed notably that marine Synechococcus have distinct sets of desaturase enzymes which have likely played a role in the colonization of different thermal niches. The results of this PhD thesis, which are discussed in the context of the Synechococcus adaptive evolution to the latitudinal gradient of temperature, raise new hypotheses for some future exciting work.
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Submitted on : Monday, March 14, 2016 - 2:06:44 PM
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Justine Pittera. Adaptations des cyanobactéries marines du genre Synechococcus au gradient latitudinal de température . Biodiversité et Ecologie. Université Pierre et Marie Curie, 2015. Français. ⟨tel-01287967⟩