Trawling the ocean virome
Microbial biodiversity surveys have often been done in a number of generally better-studied regions3, as with the San Pedro Time Series from the San Pedro Channel off the coast of Southern California. Global surveys have also been emerging, such as the Sorcerer II Global Ocean Sampling Expedition from 2004 to 2006 launched by J. Craig Venter. There are also data and samples from the Malaspina circumnavigation, an expedition devoted to data collection on ocean biodiversity and climate change that was led by the Spanish Ministry of Science and Innovation.As microbiome researcher Shinichi Sunagawa of the ETH Zurich and colleagues point out4, sequencing technologies have advanced such that they now enable systematic and quantitative global ocean surveys. These advances, in turn, made it possible to find and assess marine double-stranded DNA virus populations. This latest work on marine RNA viruses, says Sunagawa, in which he was also involved, embeds new phylum-level findings into a “robust taxonomic framework.” In his view, this research ranks in importance with the reconstruction a few years ago of a group of bacterial genomes representing more than 35 phyla that the researchers call “the candidate phyla radiation”5. If one counts viruses in with other taxonomic groups, the finding might be the largest single expansion of established microbial taxonomy, he says. And he especially likes the definition of a new basal Orthornavirae megataxon, the proposed phylum ‘Taraviricota’. This proposed phylum is one of several findings from recently published analyses of sampling data from Tara Oceans1,2, a global expedition supported by the Tara Ocean Foundation, or Fondation Tara Océan, based in France and with many partner organizations and supporters. The foundation is a major source of global data about the ocean and ocean microbes and, as its president Étienne Bourgois says, it’s a “family project.” The family business is the French fashion house agnès b., founded by his mother Agnès Troublé.Because the family cares about the sea, they bought a 36-meter schooner from Lady Pippa Blake, widow of yachtsman and explorer Sir Peter Blake, after pirates killed him during an environmental expedition in the Amazon delta, and turned it into the expedition vessel and floating science laboratory Tara, devoted to understanding and protecting the world’s marine environment. It’s a way to continue what Peter Blake started, to continue the conversation about the ocean and do research as well, says sailor-scientist Romain Troublé, executive director of the foundation and nephew of Agnès Troublé. The boat had been previously owned by explorer Jean-Louis Étienne. The foundation has supported several expeditions with Tara including the Tara Oceans and Tara Oceans Polar Circle expeditions, as well as Tara Mission Microbiomes, which is currently underway. The equilibrium of the planet “depends on the microbiome of the ocean in the same way we depend on our own microbiome,” says Romain Troublé. Viruses are part of the larger picture of how life is supported on the planet. It’s “a great mystery of the century” to decipher the roles, behaviors and functions of the ocean microbiome, including its beneficial effects. Over the last decade, he says, the expeditions have, for example, collected plankton samples from coastal waters, coral reefs and the high seas around the world for scientists to ask questions of. Microplastics in the ocean concentrate chemical pollutants such as pesticides, and microplastics appear to be substrates for distinct microbiomes. Polystyrene and polypropylene, for example, harbor different microbial communities. “We call it the plastisphere,” he says. All sample collection, not just of microplastics, happens with a view to scientific rigor to assure data quality, says Troublé. Many institutes are part of and support the expeditions through the Tara Ocean Foundation, including AtlantECO, the French Ministry of Research, the Swiss National Science Foundation, the US National Science Foundation, the European Molecular Biology Laboratory and the French National Centre for Scientific Research.Tara Oceans was an expedition initiated by EMBL researcher Eric Karsenti, here in the foreground. He is checking a rosette of Niskin bottles that collect water, and ocean microbe samples, at various depths. Sensors capture parameters such as temperature.
Credit: Fondation Tara OcéanIts expedition Tara Oceans was initiated by cell and marine biologist Eric Karsenti of the European Molecular Biology Laboratory. The expedition ran from 2009 to 2013 and covered 125,000 kilometers of ocean, taking ocean water and samples. It collected nearly 35,000 samples of viruses, algae and plankton and delivered more than 60 terabases of DNA and RNA sequences.The research community strives to follow FAIR data principles, the principles of findability, accessibility, interoperability and reusability, says Sunagawa. Tara Ocean’s data troves can be found, for instance, in the European Nucleotide Archive (ENA), Pangeaea, Cyverse, iVIRUS and on Genoscope. Other data-collection efforts target users with less programming experience and offer various types of data relevant to marine microbial research, he says: for example, the Ocean Gene Atlas, a portal to search for a gene or protein sequence to see, for instance, its abundance on an ocean map. The Ocean Barcode Atlas lets users explore, for example, operational taxonomic units (OTU) data and plankton communities from Tara Oceans and OTUs from Malaspina prokaryote data. Sunagawa also points to the Ocean Microbiomics Database and its high-quality genome-resolved information about the global microbiome, which has sequencing data from 2003 onwards and which includes Tara Oceans data as well as datasets such as the Hawaii Ocean Time-Series (HOT), the Bermuda Atlantic Time-series Study (BATS), with its collection of ocean data dating back to 1988, and BioGeotraces, with hydrographic and marine geochemical data from various expeditions.The recent publications on RNA viruses1,2, in which Sunagawa was also involved, have expanded the known diversity of these viruses, he says. They build on efforts by, for example, the research team that created and applied a cloud-based infrastructure called Serratus6, with which researchers can perform sequence alignment using bowtie2 for nucleotide sequences and DIAMOND2 for protein sequences in ‘ultra-high throughput’ on a petabase scale. Using Serratus, the team identified more than 130,000 previously unknown RNA viruses, both on land and in the oceans. The wealth of resources for microbial and viral data about the oceans is helpful to the research community, but “we could still improve the connectivity between various datasets though,” says Sunagawa. That would help, for example, with searching and finding data products that are derived from primary data, such as identifiers of individual genome assemblies, genes and metagenome assembled genomes, which are all presented in different online locations. But connecting data resources is a project that itself takes resources, and such projects are hard to get funding for.Going forward, it will be challenging, says Sunagawa, to update and keep up to date both past projects and ongoing projects such as the Global Ocean Ship-based Hydrographic Investigations program (GO-SHIP), which is focused on physical oceanography; the Antarctic Circumnavigation Expedition (ACE), on carbon-cycle marine biogeochemistry; Mission Microbiomes; and many more. “And ultimately, we will need to cross boundaries that currently separate biome-focused research to better understand processes at the sea–land–atmosphere interfaces.”Tara Mission Microbiomes has been underway for nearly two years and wraps up in October 2022. At press time, the schooner Tara was off the Angolan Coast. At the end of the expedition, it will have traveled a total of 70,000 km of ocean area around South America, Africa, Europe and Antarctica. Mission Microbiomes is part of the EU-funded AtlantECO and also includes 42 research organizations from 13 countries. The microbiome mission is collecting data on how climate change is affecting the marine microbiome, on how pollution, microplastics pollution in particular, affects the marine environments and on the beneficial impact of the ocean microbiome.Krill are small ocean crustaceans that mainly eat phytoplankton and are a food source for animals such as whales and seals. Krill play a crucial role in biogeochemical cycles.
Credit: F. Aurat, Fondation Tara OcéanChris Bowler, from the Institut de Biologie de l’École Normale Supérieure, is scientific director of the Tara Oceans consortium, was scientific coordinator of the Tara Oceans expedition and was onboard in Antarctica during the Tara Mission Microbiomes expedition to collect data on the impact of icebergs on the Weddell Sea ecosystem. The project’s scientists in Tara Mission Microbiomes, he says, are studying specific processes, including the Amazon plume, the Malvinas confluence, the impact of tabular icebergs in the Weddell Sea, the Benguela upwelling and more. The data from this expedition will be similar to those from Tara Oceans but, he says, “we will have much more contextual data related to the specific processes we have been studying.” The applied techniques are all ones that have undergone much advancement since Tara Oceans, he says. They include long-read sequencing, Hi-C sequencing to capture chromatin organization on a genome-wide basis and various types of microscopy.Data and results from previous and ongoing expeditions are impressive, says Sunagawa but “we are still data-limited in our field of research.” Geographically, sampling stations are usually still separated by hundreds of kilometers, and often they are even further apart than that. This means that what is missing is both temporal and seasonal resolution, “and we keep detecting new organisms,” he says. Tara Mission Microbiomes will help to fill in some of these gaps. The mission is unlike Tara Oceans, with its focus more on coastal areas and environmental pollutants such as microplastics. Sunagawa and his group are not currently involved with Tara Mission Microbiomes, “but we look forward to seeing the first results coming out soon.”Through photosynthesis, phytoplankton deliver oxygen to the planet. They are food for zooplankton, which are food for other marine organisms. This food web and its associated decomposition are part of the ocean’s carbon pump, in which marine viruses play an important role that scientists have only begun exploring.
Credit: M. Bardy, Fondation Tara Océan More
