Global Biogeography and Ecology of Vibrio in a Warming Planet

This doctoral thesis explores the broad-scale patterns, biogeography, and ecology of Vibrio species across the world's oceans through the molecular analysis of marine plankton samples and the use of large metagenomic data derived from global ocean sampling efforts such as the Continuous Plankton Recorder (CPR) survey and the TARA Ocean Expedition. The Vibrio genus, including clinically important pathogenic species such as V. cholerae, V. parahaemolyticus, V. vulnificus, and V. alginolyticus, plays a significant role in aquatic ecosystems and human health. Through deep metagenomic shotgun sequencing and the global oceanic samplings of the TARA Ocean expedition, approximately 40 terabases of data from 1,500 TARA metagenomes were analyzed, employing a custom bioinformatics pipeline. The pipeline permits to download, extract, and analyze Vibrio reads from complex metagenomic data. This approach enabled a detailed examination of Vibrio diversity, biogeography and dispersal patterns via ocean currents and their ecological interactions within major biological corridors in the ocean as a planetary interconnected ecosystem (see chapter 3). Results showed that Vibrio represents a major player in the oceans being the 7th most abundant group in the oceans with differentiated communities living in the water fraction and attached to plankton. While free-living communities showed a well-defined biogeographical pattern, plankton-attached populations showed a strong association with small (20-180 µm) plankton, which governed its distribution and connectivity across the oceans following the major migratory routes. These findings have strong implications for the demography, population dynamics and evolution of Vibrio species, including those species pathogenic for humans and animals. In addition, in this thesis, the large-scale impact of the 2016 marine heatwave (MHV) on plankton associated Vibrio communities was investigated along an ~800 km transect in the Great Barrier Reef (GBR, Australia) from November 2014 to August 2016 (see chapter 4). Novel methodologies for pathogen detection in CPR samples collected in the GBR by the Australian Continuous Plankton Recorder (AusCPR) were developed. 16S rRNA gene metabarcoding of archived plankton samples were applied showing a significant increase in bacteria belonging to the genus Vibrio during and after the 2016 heatwave. Notably, Droplet Digital PCR and targeted metagenomic analysis applied on samples collected four months after the MHW event revealed the presence of several potential pathogenic Vibrio species associated with diseases in aquatic animals. Overall, the 2016 MHW significantly impacted the surface picoplankton community and fostered the spread of potentially pathogenic bacteria across the GBR providing an additional threat for marine biodiversity in this area. These efforts, integrating extensive sequencing analysis with environmental data, illustrate how large and global scale concepts can help integrate Vibrio biological complexity in relation to climate change and oceanic conditions; as well as for assessing ecosystem changes for our planet in the Anthropocene epoch.