Bacterial communities dynamics in response to phytoplanctonic bloom in the Arctic Ocean and identification of the microbial players in the organic matter degradation

• Main Author: Dadaglio, Laëtitia
• Other Authors: Laboratoire d'Océanographie Microbienne (LOMIC), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Observatoire océanologique de Banyuls (OOB), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Sorbonne Université, Fabien Joux, Ingrid Obernosterer
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2018
• Subjects: Bacterial strains; Bacterial activity; Biodegradation; Spatial and temporal dynamics; Bacterial community composition; Arctic Ocean; Phytoplankton bloom; Dissolved organic matter; Bloom phytoplanctonique; Matière organique dissoute; Composition des communautés bactériennes; Dynamiques spatiales et temporelles; Biodégradation; Activité bactérienne; Souches bactériennes; Océan Arctique; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDV.MP.BAC]Life Sciences [q-bio]/Microbiology and Parasitology/Bacteriology; Arctic; Arctique*; banquise; Global warming; Phytoplankton
• Online Access: https://theses.hal.science/tel-02614103; https://theses.hal.science/tel-02614103/document; https://theses.hal.science/tel-02614103/file/DADAGLIO_Laetitia_2018.pdf

Global warming leads to a drastic decrease in the coverage and thickness of the ice pack leading to longer and more intense Arctic phytoplankton blooms. The increase in primary production associated to the phytoplankton bloom could induce pronounced changes in the functioning of the Arctic ecosystem, in particular the bacterial communities (BC) implicated in the degradation of organic matter (OM). The objectives of the present thesis were to (1) describe the in situ temporal and spatial dynamics of the BC during the ice retreat and the spring phytoplankton bloom, and (2) identify experimentally the bacterial players responsible for the degradation of OM excreted by different Arctic microalgae. The results show a rapid response of the BC to the phytoplankton bloom during the ice retreat, with simultaneous maxima in chla and bacterial abundance. Modifications in the BC composition (BCC) appear prior and during the phytoplankton bloom with a decrease in the bacterial diversity. The rapid acclimation of the BC to the fresh phytoplankton OM could be due to preceding OM production by ice microalgae or by algal mats attached to the ice. Ice retreat and phytoplankton bloom development lead to a BC dominated by Oceanospirillales and Flavobacteriaceae. Field and experimental results highlight Polaribacter as a key player in the degradation of OM produced during diatom dominated phytoplankton blooms in the Arctic Ocean. Our results also suggest a modification in the phytoplankton community composition (towards picoeukaryotes) linked to global warming could have consequences on the activity and composition of the associated BC. Le réchauffement climatique conduit à une diminution drastique de l’étendue et de l’épaisseur de la banquise entrainant un allongement et une intensification du bloom phytoplanctonique Arctique. L’augmentation de la production primaire pourrait modifier le fonctionnement de cet écosystème ainsi que les communautés bactériennes (CB) impliquées dans la dégradation de la matière organique (MO). Les ...