As part of this project, we successfully established marine aquaculture systems for Hydractinia and related species, and isolated representative symbiotic bacteria capable of inducing morphogenesis in competent Hydractinia larvae as well as in other marine eukaryotes. Hydractinia specimens were collected during seasonal field expeditions from multiple stations worldwide, enabling us to monitor seasonal and location-specific effects on their associated microbiomes.
Employing state-of-the-art sequencing technologies, we conducted whole-genome sequencing on a diverse set of unique bacterial and fungal isolates to support their genetic characterization and manipulation. Chemical analyses of these bacterial species, performed using advanced metabolomic techniques, uncovered several morphogenic signaling molecules associated with bacterial outer membranes or biofilm matrices, which are detected by competent larvae. Notably, we found that these morphogens act synergistically, eliciting a stronger morphogenic response than individual compounds or axenic bacterial biofilms alone. Furthermore, we demonstrated that outer membrane vesicles (OMVs) represent an exceptionally effective delivery mechanism for these bacterial signals.
Through genome-mining strategies, we also identified novel antimicrobial compounds from both aerobic and anaerobic bacterial and fungal species associated with Hydractinia. These include globally abundant bacteria-derived aminolipids with antimicrobial activity, sphingolipids, and in particular bacterial sulfonosphingolipids, which function as crucial inter- and intracellular signaling molecules. In addition, we discovered complex sphingosine-derived natural products that act as selective enzyme inhibitors. Using total synthesis approaches, we developed chemical probes based on these natural products, enabling protein profiling experiments to identify their putative protein targets.
Microbial profiling further provided the first detailed insights into the beneficial microbiome of Hydractinia, allowing us to explore its biosynthetic potential in depth. These studies not only revealed the composition of the microbiome in relation to biotic factors but also elucidated its catabolic and anabolic capacities, offering valuable perspectives on protective and nutritional symbiotic relationships. Moreover, we identified bacterial endosymbionts unique to this system and explored their potential contributions to the health and resilience of the eukaryotic host.
Overall, our work has provided unprecedented molecular insights into the cross-kingdom communication strategies and cellular mechanisms underlying bacteria-induced morphogenesis and host protection in the marine invertebrate Hydractinia and related species.
