Marine biologists on the Tara Oceans global oceanographic research expedition have identified nearly 196,000 marine virus species, which vastly exceeds the 15,000 known from prior ocean surveys and the approximately 2,000 genomes available from cultured viruses of microbes.
Microbes drive most ecosystems and are modulated by viruses that impact their lifespan, gene flow, and metabolic outputs. However, ecosystem-level impacts of viral community diversity remain difficult to assess due to classification issues and few reference genomes. Gregory et al established an 12-fold expanded global ocean DNA virome dataset of 195,728 viral populations, now including the Arctic Ocean. Image credit: Arek Socha.
“Viruses are these tiny things that you can’t even see, but because they’re present in such huge numbers, they really matter,” said Dr. Matthew Sullivan, a microbiologist at the Ohio State University.
“We’ve developed a distribution map that is foundational for anyone who wants to study how viruses manipulate the ecosystem. There were many things that surprised us about our findings.”
Dr. Sullivan and colleagues collected the samples between 2009 and 2013 during expeditions aboard a single sailboat, the Tara.
The researchers studied not only the water samples for viruses, but also other microbes and other living creatures.
“We filtered the samples to analyze organisms ranging in size from viruses to fish eggs,” Dr. Sullivan said.
Among the surprises was the existence of 195,728 marine virus species.
Additionally, meta-community analysis showed that the viruses were organized into five distinct ecological zones throughout the entire ocean, which was unexpected given the fluid nature of the oceans and the complexity of many of the marine regions.
Also, despite the paradigm from larger organisms that species diversity is highest near the equator and lowest near the poles, the scientists collected an extensive number of samples in the Arctic compared to previous studies of ocean life and found a biodiversity hotspot in the Arctic Ocean.
“Having a more complete picture of marine viral distribution and abundance will help us to determine which viruses we should be focusing on for further studies,” the biologists said.
“Additionally, the maps based on this research establish a baseline for other collection efforts going forward, which can help to answer questions about how levels of microorganisms change over time, in response to both seasonal variation and climate change.”
“Previous ocean ecosystem models have commonly ignored microbes, and rarely included viruses, but we now know they are a vital component to include,” Dr. Sullivan said.
The findings appear in the journal Cell.
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Ann C. Gregory et al. Marine DNA Viral Macro- and Microdiversity from Pole to Pole. Cell, published online April 25, 2019; doi: 10.1016/j.cell.2019.03.040
