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Effect of environmental variations on bacterial communities dynamics : evolution and adaptation of bacteria as part of a microbial observatory in the Bay of Brest and the Iroise Sea

Abstract : Marine bacteria play a key role in thefunctioning of marine ecosystems. In these environments they form complex communities that are extremely dynamic in time and space, whoseglobal diversity is still largely unknown. Understandingthe mechanisms that govern their dynamic is essential to better understand their role in ecosystems and anticipate the influence of global changes andanthropogenic pressures. This thesis presents theset-up of a microbial observatory in the Bay of Brest and the Iroise Sea. Bacterial community dynamics inrelation to the environment were first studied using 16S amplicon sequencing. The presence of aseasonal front in the Iroise Sea deeply structuresbacterial communities that will vary with the different water masses. But one of the most structuring parameters is the heterogeneous distribution of phytoplankton, which would selects heterotrophic bacteria adapted to different organic matter concentrationsIn the Bay of Brest, analysis of the first 3 years oftemporal monitoring at the SOMLIT station shows that bacterial communities present remarkable recurrent seasonality. This seasonal dynamic presents a rapid change when spring blooms areimplemented with the rapid and intense response of several heterotrophic taxa. Finally, a metagenomicapproach has allowed us to reconstruct the genome (MAG) of the most abundant bacterium found on these two surveys, belonging to the Rhodobacteraceae family. Its genome shows unusual characteristics for this family, with features typical of streamlined genomes. However, contrary to what is generally described for such bacteria, it is adapted to an environment rich in organic matter, representing up to 20% of the microbial community during bloom periods. These results highlight theimportance to explore communities both in terms of their overall dynamics and functionality.
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Clarisse Lemonnier. Effect of environmental variations on bacterial communities dynamics : evolution and adaptation of bacteria as part of a microbial observatory in the Bay of Brest and the Iroise Sea. Ecosystems. Université de Bretagne occidentale - Brest, 2019. English. ⟨NNT : 2019BRES0030⟩. ⟨tel-02953054⟩

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