Our first goal is to define the microbiome that is unique to the cosmopolitan alga E. huxleyi. This alga displays massive blooms in the ocean that stretch over thousands of kilometers and can be seen from space. We have now generated an unique microbiome archive of samples collected from five E. huxleyi blooms in different oceanic provinces of the Atlantic Ocean from Iceland to Patagonia. We analyzed bacterial growth and diversity during induced blooms in a mesocosm setup in the Fjords of Bergen, using 16S rDNA. This setup enabled high temporal sampling which provided initial insights into the microbial composition at different phases of the blooms. Furthermore, we provided results on the composition of the planktonic and of the particle-associated microbiome in the bloom. The latter can shed light on the specific microbial community that regulates carbon export to the seabed. Furthermore, we revealed new players in the recycling of algal biomass during viral infection. These were a group of eukaryotic heterotrophs, called Thraustochytrids, that can rival the free-living bacteria as potential recyclers of dissolved organic matter (Vincent et al. Nature Communications 2023). Our next goal is to further define the unique microbiome of virus-induced bloom demise from several locations in the Atlantic Ocean and to better predict bacterial functional phenotypes and key metabolic pathways using metagenomics and metatranscriptomics.
Next, we aimed to examine the unique microbial lifestyle in response to the viral shunt and its derived metabolites. For this aim, we developed an innovative approach to study the microbial lifestyles of the bacteria that thrived on viral-derived DOM (vDOM). We collected and preserved a large archive of Bloom-Associated Microbiomes (BAMs) from E. huxleyi blooms across the Atlantic Ocean. As a foundation for this goal, we successfully generated a synthetic community composed of alga, viruses and bacteria isolated from E. huxleyi bloom, that reproduced the dynamics observed in the ocean. Intriguingly, we revealed that adding BAMs to virus-infected E. huxleyi enhanced lysis of the algal culture as compared to virus infection alone. This important phenotype was termed ‘synergy’, a phenomenon known from the biomedical field but was never investigated in the marine environment. We are currently performing population genetic analysis in order to gain insight into the main bacteria taxa that drive this process and to identify the key metabolic pathways that are tuned towards virus-induced bloom demise in a specialized microbiome.
One of the main aims of our project is to map the unique metabolic landscape of viral infection in algal blooms in the ocean. In our new study, we mapped the viral shunt in large-scale blooms across the Atlantic Ocean, by applying metabolic biomarkers that are highly specific to viral infection of coccolithophore blooms. Using these specific metabolites that are generated during host-virus interactions, we developed specific organohalogens as a novel group of metabolic biomarkers to virus-induced demise of E. huxleyi blooms in the ocean. These specific metabolic footprints enabled sensitive detection of infections in the natural environment akin to their use as a diagnostic tool in the biomedical field. We found these metabolites to be highly stable in the extracellular milieu, thus providing a sensitive metabolic signature to track the impact of viral lysis in the ocean.
