PhD student: Maxime BEAUVAIS

Supervisors (ASR) : François-Yves Bouget (50% LOMIC)
Co-spervisor (ASR) : Pierre Galand (50% LECOB)

General information:
Marine planktonic microbes play a key role in global biogeochemical cycles. In temperate regions, microbial communities have a temporal dynamics featured by a succession of species controlled by biotic interactions under the influence of physical and chemical parameters. The complexity of the interactions linking the different compartments of these ecosystems remains largely unknown. Through a 7 year timeseries at SOLA point in the Banyuls Bay (2007-2014) we showed a marked seasonality both in eukaryotic microalgae, bacteria and Archeae (Lambert et al., ISME J 2018). Still, the analysis of microbial network unveiled a variability in cooccurences of microorganisms in a higher resolution timeseries (2014-2017) at SOLA (Lambert et al., under review). We also evidenced variations in the biodisponibility of B1 vitamins which are required for the growth of photosynthetic picoeukaryotes such as mamiellophyceae (Paerl et al., ISME J 2017).The objective of the thesis is to go deeper in the understanding of the system and of its global role and vulnerability to global changes by identifying the biotic factors regulating seasonal rhythms of microbial communities in the bay of Banyuls (SOLA point). The novelty of the subject relies in the specific study of the role of trophic interactions between eukaryotes and prokaryotes of the sediments and the water column with a specific focus on metabolites such as vitamins in the regulation of blooms. The project relies on an original approach combining the in situcharacterization though OMICs approaches and experimentation under controlled conditions of light and temperature in the lab. The work will focus on the interactions between bacteria and photosynthetic picoeukaryotes in the initiation of phytoplanktonic blooms.

Thefollowing points will be studied:
1) Monitoring of microbial diversity in the water column and the sediment at SOLA during prebloom, bloom and postbloom of mamiellophyceae using metabarcoding during two winters (December to April).
2)The effect of addition of microorganisms or porewater from sediments on the growth of phytoplanktonic microorganisms of the water column.
3)The effect of addition of B1, B7 and B12 vitamins on microbial communities of phytoplankton in prebloom, bloom or postbloom.

The project is connected to a collaborative project (Preselected ANR BIORYTHMIC 2020) with the LECOB (Pierre Galand, INEE) which is expert in ecology and genomics of microorganisms.

PhD student: Victor Le Layec

Supervisor: Stéphane Hourdez

General information:
The thesis focuses on the study of the adaptations of hydrothermal organisms to extreme conditions, in a phylogenetic framework. The thesis work focuses on a family of annelids (the Polynoidae) that are found not only in hydrothermal but also in non-hydrothermal abyssal environments, in Antarctica, and in temperate marine environments. This allows for a series of contrasting living conditions to study in particular the adaptation to hypoxia but also to temperature.

Ph student: Adrien Tran Lu Y

Supervisor: François Bonhomme (ISEM)
Co-supervisor: Stéphane Hourdez

General information :
To estimate the resilience of deep hydrothermal species, functional connectivity between sites, which depends on the dispersal capacities of the species, is a fundamental criterion for the long-term maintenance of populations in the face of the potential impact of mining on the degree of fragmentation of this habitat, which is also temporally unstable. This connectivity will be approached at several time and space scales by population genomics methods on a series of species chosen according to their life history traits and their distribution in the rear-arc basins of the Southwest Pacific.

PhD student : Victoria LOUIS

Supervisor (HDR): Franck Lartaud (LECOB)
Co-supervisor: Laurence Besseau (BIOM)

• General information:
• The general aim of this thesis is to study the role of biological clocks on synchronization processes of biomineralization of the shell in the mussel M. galloprovincialis. The objective is to determine if the environment acts directly on the shell biomineralization process or if a biological clock allows the bivalve to anticipate the environmental circadian variation thus regulating the shell growth. We hypothesized that photoperiod (day/night alternation over a 24h cycle), temperature and/or trophic resources would synchronize the biological clock, alone or in combination, leading to control the rhythmic activity of shell biomineralization process in the Mediterranean mussel Mytilus galloprovincialis.

In order to achieve these objectives, different cruises in the Bay of Banyuls will be done at circadian scales, and in vitro experiments at the OOB will test the role of the main drivers (photoperiod, temperature, feeding). Part of the work will be dedicated to the analysis of the growth patterns of the shell of M. galloprovincialis, obtained after chemical labelling technique (calcein) and recapture. Sclerochronological analysis of thin sections of the shells will be reached by fluorescence microscopy and scanning electron microscopy (SEM). A transcriptome analysis of the main molecular players involved in biological clocks (clock genes such as Clock, Bmal, Cry, Per and Rorb) and genes for metabolic activity and biomineralization (carbonic anhydrase, , nacrein, chitinase et Ca²⁺ ATPase), will be developed at different sampling points of the 24h cycle by a broadband approach (NanoString technology). The analysis of the amount of tissue biomarkers (lipids, proteins, carbohydrates) accessed by colorimetry will give a first indication of the assimilation of energy reserves, which will be complemented by the characterization of the variability of the food intake, approached by metabarcoding analysis of the stomach contents, achieved by high-throughput sequencing (Illumina MiSeq) of 16S and 18S rRNA genes.

Finally, the study will benefit from data of the Prime|80 project -TEMPO- dealing with the dynamic conditions and the potential variation of trophic resources in the mussel habitat, to carry out a comparative study of the different ecological compartments likely to initiate a rhythmic response of activity in this species.