3. Understanding the role of secondary metabolites of bacterial origin on symbiotic associations

Marine invertebrates (sponges, cnidarians) are a well-know source of novel bioactive compounds, and recent developments in genomics, genetics and metagenomics, have demonstrated that some classes of compounds, in particular polyketides and non-ribosomal peptides are of microbial origin. In addition, some potent secondary metabolites (enediynes) have also been recently discovered in lichen-associated heterotrophic bacteria. These findings point to the hypothesis that these secondary metabolites play a role in these symbiotic associations (for example, deterring predation or excluding non-symbiotic microorganisms). One of the first steps in comprehending this putative role is demonstrating the microbial origin of major bioactive compounds in the holobionts.

Marine Sponges
We are currently studying such a possibility in the marine sponge Crambe crambe, known for the production of high concentrations of highly bioactive (antimicrobial, antitumoral) pentacyclic guanidine alkaloids such as crambescine and crambescidine. Until recently these compounds were believed to be produced by the sponge, since microorganisms were reported as absent from their tissues. The work of our doctoral student Julie Croué (who is co-directed by Nataly Bontemps at the Laboratoire de Chimie des Biomolécules et de l’Environnement, University of Perpignan) has unequivocally demonstrated the presence of bacteria in this sponge, and more significantly, that the community is largely composed of a single bacterial species. While we will continue efforts to isolate these microorganisms, we have started to employ a number of metagenomic approaches (fosmid cloning, ion torrent shotgun sequencing and single cell genomics) in order to better understand the role of this bacterium in this symbiosis, and the intriguing possibility that this organism might be involved in the biosynthesis of these compounds. We also collaborate with Prof Olivier Thomas (Univ Nice) to examine the implication of bacteria (or lack thereof) in the biosynthesis of guanidine alkaloids in Crambe crambe.

Marine Lichens
We colaborate with Drs. Sophie Tomasi and Pierre Van de Weghe a the Institut des Sciences Chimiques de Rennes (UMR 6226 CNRS/Université Rennes I, France) and the University of Graz (Austria), and we have the ANR project (ANR MALICA) funded to study secondary metabolites from bacteria associated with coastal and marine lichens. Recent studies have reported that, in addition to fungal and algal partners, lichens are a stable consortium containing other microorganisms, including parasitic or endophytic fungi and bacteria. These microorganisms are thought to be an interesting source of biologically active molecules since lichen-derived natural products exhibit a great diversity of biological effects (antimicrobial, anti-inflammatory, analgesic, antipyretic, antiproliferative and cytotoxic activities). In addition to the goals of the MALICA project, we are studying the diversity of microorganisms associated to a large diversity of marine and littoral lichens from various locations,and the production of secondary metabolites by these microorganisms. Beyond the hope that we will develop new cancer drugs, this work will contribute to the better understanding of the lichen-microorganisms interactions, the chemical ecology of the system, and the microbial ecology of marine lichens in general.

Marine seagrasses
Finally, the development of research in the symbiosis between marine seagrasses and bacteria (see subtopic 2), will represent yet another system where the role of secondary metabolites of bacterial origin in a symbiosis can be assessed.

Some recently publications (some in preparation) in this topic include

• Croue J, West NJ, Escande ML, Intertaglia L, Lebaron P, Suzuki MT (2013) A single betaproteobacterium dominates the microbial community of the crambescidine-containing sponge Crambe crambe. Sci Rep 3:2583
• Croué, J., S. Antony-Babu, L. Intertaglia, G. Hogrel,, Lebaron, P. and M.T. Suzuki. Diversity of culturable bacteria associated with the marine sponge Crambe crambe using multiple cultivation approaches (in preparation).
• Parrot, D., S. Antony-Babu, L. Intertaglia, M. Grube, S Tomasi. and M.T. Suzuki. Littoral lichens as a source of potentially bioactive Actinobacteria (submiitted to Appl Microbiol Biochnol).