Exploration of molecular interplay occurring in marine microbial communities

Phytoplankton are known to account for at least 50% of the total photosynthetic activity taking place on the planet. These microorganisms are therefore responsible for over half of the carbon fixation and as much for the production of the oxygen found in the atmosphere. Phytoplankton are mainly represented by diatoms, microalgae and cyanobacteria. Among cyanobacteria, microbes from the Prochlorococcus and Synechococcus genus - also called picocyanobacteria - are the most abundant on Earth and as such, it is highly important to improve our understanding of their biology.
The Ph.D project will focus on exploring how Synechococcus cells interact at the molecular level with their environment and especially within marine microbial communities. A study of various Synechococcus strains exoproteome, previously carried out in the lab, showed that all strains secrete a highly-conserved protein that could be involved in quorum-quenching and, in turn, the regulation of the heterotrophic bacterial community that surrounds phytoplankton. Part of the Ph.D. project will set out to identify and characterize this protein to understand its function and its significance for the marine bacterial community.
Co-cultures of Synechococcus and Salinispora tropica - a heterotrophe marine bacteria found in sediments - grown in the lab showed that Synechococcus dies in presence of Salinispora. Interestingly, Synechococcus eventually grew back in one of the co-cultures even though Salinispora was still present. Salinispora is known to produce many secondary metabolites with cytotoxic and anti-cancer activity. Part of the Ph.D. project will set out to identify and characterize any novel antimicrobial metabolites produced by Salinispora to kill Synechococcus. Also, we will study how in this particular culture, Synechococcus adapted to survive this yet unknown killing mechanism.