• Le 06 juin 2019
    De 11:00 à 12:00
    Campus Lombarderie
    Amphi A- bâtiment 1

Le Laboratoire des Sciences du Numérique de Nantes (LS2N - Université de Nantes - CNRS - Centrale Nantes - IMT Atlantique) accueille le Docteur Julie LaRoche (Dalhousie University, Nova Scotia, Canada) lors d'un séminaire (en anglais) ouvert à tous, le jeudi 6 juin prochain.

Dynamics of microbial community structure and marine dinitrogen fixation at a microbial observatory in the Northwest Atlantic Ocean

Dr Julie LaRoche
Professor and Canada Research Chair in Marine Microbial Genomics and Biogeochemistry, Department of Biology, Dalhousie University, Nova Scotia, Canada

Primary productivity is limited by the availability of fixed nitrogen in large regions of the oceans. Dinitrogen fixation, the only biological input pathway into the marine N cycle, is an energetically expensive biochemical process that reduces N2 gas into NH3, a form of fixed nitrogen that is readily incorporated into biomolecules. The nitrogen fixers, or diazotrophs, are a selected group of prokaryotic microorganisms that can carry out this biochemical process. Historically, marine nitrogen fixation was thought to be a process carried out primarily by cyanobacteria and important mainly in the tropical and subtropical oligotrophic waters. Recent realization concerning the wide diversity of marine microbes harboring the nitrogenase enzyme indicates that we do not fully understand the roles of the diverse diazotrophs that populate the ocean. In the context of the Ocean Frontier Institute located at Dalhousie University, the microbial community structure and function in Northwest Atlantic (NWA) have been assessed through next-generation sequencing of hypervariable regions of 16S and 18S rRNA genes, nifH gene and metagenomics at existing time-series stations since 2014. The nifH gene, a marker gene for diazotrophy, has shown that both cyanobacterial and non-cyanobacterial diazotrophs are members of the microbial communities in our NWA microbial observatories. The lecture will focus on the microbial community structure in the NWA, with a specific attention to the diazotrophs. In particular, the potential metabolic pathways identified from the genome annotation of a novel bacterial isolate, belonging to a clade of gamma-proteobacteria widely distributed in the Tara expedition database, will be discussed in a global context.