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Home > Thèses et HDR > Thèses en 2020

21/07/2020 - Rose LAYTON

by Laurent Krähenbühl - published on , updated on


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Rose Layton defends his PhD on July 21, 2020 at 4:00 PM.
Place : Ecole Centrale de Lyon, Bâtiment W1, visio conference only.

Title : Microbial community structure and function across the seawater-sea ice-frost flower-snow-atmosphere continuum

Jury :
- L. WHYTE Professeur
- J. MIKUCKI Associate Professor
- J. BOWMAN Assistant Professor
- P. SIMONET Directeur de Recherche CNRS
- M. JEBBAR Professeur
- T. VOGEL Professeur
- C. LAROSE Chargée de Recherche CNRS - HDR

Abstract :
Sea ice is an important and extensive (34 million km2 ) ecosystem and has a diverse array of ecologically important roles; from providing a habitat to micro- and macro- organisms to impacting the global energy budget. The sea ice landscape is experiencing drastic changes as a result of climate change. These changes can be seen in the shift of dominant ice type of Polar Regions (from MYI to FYI) and consequently the expansion of associated environments such as brine wetted snow and frost flowers. Although these ecosystems are known to host a diverse array of microorganisms, our understanding of the consequences of climate change on these communities is limited. The overarching goal of this thesis was to assess microbial colonisation, community adaptation and dynamics in relation to sea ice formation and the developing habitats at different spatial and temporal scales. In order to achieve this, next generation sequencing techniques were employed to taxonomically and functionally interrogate laboratory and natural sea ice, snow and frost flower models. The first objective addressed how eukaryotic and bacterial populations established and partitioned in young sea ice and frost flowers. To avoid interference from prevailing conditions, local geography and ocean currents, a sea ice chamber microcosm setup was utilised. The taxonomic and functional partitioning of bacteria into distinct niches (frost flower, brine, ice matrix and seawater) supported the hypothesis of niche based selection and was bolstered by the appearance of archetypal sea ice bacteria, not identified in the seeding seawater. In contrast, the consistency of eukaryotic communities across the profile identified the influence of stochasticity. Our data suggested that bacterial enrichment in sea ice occurred at a similar rate as previously observed, despite minimal diatom representation. This stands in contrast to a widely circulated hypothesis that proposes bacterial enrichment is linked to diatom attachment. Our second objective was to identify the environmental factors that influenced community selection across sea ice and snow communities. If microbial community assembly is driven by the prevailing conditions, corresponding adaptations should be reflected in the metagenomes. Indeed, functional signatures including motility, chemotaxis, response to UV and genetic transfer were all found in greater abundance in the saline snow and some ice horizons relative to the seawater, presenting possible drivers of functional potential.
A final objective was to survey the taxonomic and functional potential of frost flowers and saline snow. In both microcosm (frost flowers) and field experiments (saline snow), a taxaspecific enrichment was observed. Colwellia and Glaciecola were overwhelmingly dominant in brine-fed snow environments, independent of temporal or spatial factors. Metagenomic assembled genomes (MAGs) suggested that UV repair mechanisms and the ability to gain a growth advantage from light using proteorhodopsin proton pumps may underscore their success in these habitats.

Key Words:
colonisation, adaption, microbial ecology, sea-ice environments, climate change