title: Connecting thermal physiology and latitudinal niche partitioning in marine Synechococcus.
abstract: Marine Synechococcus cyanobacteria constitute a monophyletic group that displays a wide latitudinal distribution, ranging from the equator to the polar fronts. Whether these organisms are all physiologically adapted to stand a large temperature gradient or stenotherms with narrow growth temperature ranges has so far remained unexplored. We submitted a panel of six strains, isolated along a gradient of latitude in the North Atlantic Ocean, to long- and short-term variations of temperature. Upon a downward shift of temperature, the strains showed strikingly distinct resistance, seemingly related to their latitude of isolation, with tropical strains collapsing while northern strains were capable of growing. This behaviour was associated to differential photosynthetic performances. In the tropical strains, the rapid photosystem II inactivation and the decrease of the antioxydant β-carotene relative to chl a suggested a strong induction of oxidative stress. These different responses were related to the thermal preferenda of the strains. The northern strains could grow at 10 °C while the other strains preferred higher temperatures. In addition, we pointed out a correspondence between strain isolation temperature and phylogeny. In particular, clades I and IV laboratory strains were all collected in the coldest waters of the distribution area of marine Synechococus. We, however, show that clade I Synechococcus exhibit different levels of adaptation, which apparently reflect their location on the latitudinal temperature gradient. This study reveals the existence of lineages of marine Synechococcus physiologically specialised in different thermal niches, therefore suggesting the existence of temperature ecotypes within the marine Synechococcus radiation.
authors.affiliation: 1] University Pierre and Marie Curie (Paris 06), UMR 7144 Adaptation and Diversity in Marine Environments, Marine Phototrophic Procaryotes (MaPP) Team, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France [2] Centre National de la Recherche Scientifique, UMR 7144 Adaptation and Diversity in Marine Environments, Oceanic Plankton Group, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France.
authors.forename: Justine
authors.initials: J
authors.lastname: Pittera
authors.affiliation: 1] University Pierre and Marie Curie (Paris 06), UMR 7144 Adaptation and Diversity in Marine Environments, Marine Phototrophic Procaryotes (MaPP) Team, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France [2] Centre National de la Recherche Scientifique, UMR 7144 Adaptation and Diversity in Marine Environments, Oceanic Plankton Group, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Humily
authors.affiliation: University of Caen-Basse Normandie et Centre National de la Recherche Scientifique, Institut d'Ecologie et d'Environnement, FRE 3484 Biologie des Mollusques Marins et des Ecosystèmes associés, Caen, France.
authors.forename: Maxine
authors.initials: M
authors.lastname: Thorel
authors.affiliation: 1] University Pierre and Marie Curie (Paris 06), UMR 7144 Adaptation and Diversity in Marine Environments, Marine Phototrophic Procaryotes (MaPP) Team, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France [2] Centre National de la Recherche Scientifique, UMR 7144 Adaptation and Diversity in Marine Environments, Oceanic Plankton Group, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France.
authors.forename: Daphné
authors.initials: D
authors.lastname: Grulois
authors.affiliation: 1] University Pierre and Marie Curie (Paris 06), UMR 7144 Adaptation and Diversity in Marine Environments, Marine Phototrophic Procaryotes (MaPP) Team, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France [2] Centre National de la Recherche Scientifique, UMR 7144 Adaptation and Diversity in Marine Environments, Oceanic Plankton Group, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Garczarek
authors.affiliation: 1] University Pierre and Marie Curie (Paris 06), UMR 7144 Adaptation and Diversity in Marine Environments, Marine Phototrophic Procaryotes (MaPP) Team, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France [2] Centre National de la Recherche Scientifique, UMR 7144 Adaptation and Diversity in Marine Environments, Oceanic Plankton Group, Station Biologique de Roscoff, Place Georges Teissier, CS 90074, Roscoff cedex, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Six
mesh_terms: D001267:Atlantic Ocean; D003080:Cold Temperature; D010788:Photosynthesis; D010802:Phylogeny; D012623:Seawater / Q000382:microbiology*; D046940:Synechococcus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D013696:Temperature