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.