Research Uncovers Vast Unknown Microbial Genes in Antarctic Waters

The Southern Ocean - vast, boundless waters surrounding Antarctica - plays an outsize role in global climate, largely thanks to tiny drifting organisms called plankton that soak up carbon. Reporting in Nature Communications on March 9, researchers have completed the most comprehensive survey to date of DNA associated with these microbes, paving the way for a better understanding of their role in climate change. 

The study stems from nearly a decade of genetic analysis conducted by biogeochemist Nicolas Cassar, Lee Hill Snowdon Bass Chair at Duke University's Nicholas School of the Environment, together with researchers from the European Institute for Marine Studies and other international collaborators.

The Southern Ocean is massive and plays a disproportionate role in terms of heat and carbon uptake from the atmosphere. We wanted to better understand microbial diversity in the region, because those microbes affect the carbon cycle in different ways."

Nicolas Cassar, Lee Hill Snowdon Bass Chair, Duke University's Nicholas School of the Environment

For example, certain microscopic marine organisms called phytoplankton are responsible for half the photosynthesis on Earth, meaning they take up a substantial amount of carbon dioxide from the atmosphere.

The researchers analyzed DNA from water samples collected throughout the Southern Ocean during a three-month expedition in late 2016 and early 2017. After sequencing the DNA, they cross-referenced their results with data on known genes, called gene catalogs. Next, they divided their samples into groups based on genetic similarities, such as adaptation to cold temperatures.

Remarkably, at least a third of the genes identified are missing from existing marine gene catalogs, underscoring how little we know about microbial life on our planet, according to Cassar.

"When we looked at the databases, a huge portion of these genes just wasn't there. That's a sign we're charting largely uncharacterized genetic territory," he said.

The analysis also indicated that microbial communities are not evenly distributed in the Southern Ocean. Rather, they exist in distinct microbial ecosystems shaped by ocean circulation. Some live in cold surface water and others in deep waters, for instance.

The next step is to dig deeper into this newfound genetic diversity to ultimately understand how it affects, and is affected by, climate change, according to Cassar. 

"Microbes regulate much of the ocean's chemistry," he said. "To understand how the Southern Ocean will influence future climate, we need to understand the genes that control those microbial processes."