The decrease of anthropogenic phosphorus (P) inputs since the 1980s, with a maintenance of nitrogen inputs (N) have led to an increase in N: P ratios in coastal areas. P-Limitationinduces a strong secretion of organic nitrogen compounds (NOD) in some haptophytes and may increase the extracellular toxicity of certain toxic species. The project Inter-Centers IFREMER IMOTEP aims to assess the role of bacteria in the phycosphere on the compounds secreted by phytoplankton limited by P.
Different toxic and non-toxic species of haptophytes and dinoflagellates are cultured in specific photobioreactors, in P-lim and absence of bacteria. The extracellular fractions are isolated and characterized. On the other hand, around fifteen cultivable bacteria selected for beeing associated to microalgae are cultivated on FECs to assess their ability to develop individually.The impact of bacteria on the secreted molecules is studied by co-cultures of microalgae and mix of selected bacteria. Bacterial populations are analysed by metabarcoding. The impact of bacteria on FECs is assessed at the biochemical (DIN / DON), toxic (MS analysis), enzymatic (activity tests), proteomic (shotgun analyzes), and bioactivity (hemolytic tests) level. The results help to better understand the role of microbial interactions in the ecological functionality of phytoplankton populations.
This inter-center project is funded by the IFREMER Scientific Department and benefits from the expertise of the 4 involved IFREMER laboratories: LER / BO (Concarneau); BRM / PBA (Nantes); DYNECO / PHYC (Nantes) and DYNECO / PELAGOS (Brest)