Woods Hole, Mass., Mar 19: A new study led by the Woods Hole Oceanographic Institution (WHOI) and Columbia University has identified a diverse set of molecules released by marine phytoplankton that fuel microbial life and help regulate Earth’s carbon cycle. The findings shed light on the previously hidden chemical interactions that move billions of tons of carbon through the surface ocean each year.
Phytoplankton, microscopic photosynthetic organisms, absorb carbon dioxide and convert it into organic carbon, supporting both oxygen production and microbial metabolism in the ocean. While scientists have long known that phytoplankton transfer carbon to microbial communities, the specific compounds involved—small, rapidly consumed molecules—have remained largely undetectable until now.
“For this study, we grew six representative phytoplankton species under controlled laboratory conditions,” said Yuting Zhu, co-lead author and former WHOI postdoctoral investigator, now at Old Dominion University. “Using a chemical-tagging method developed at WHOI, we quantified the biologically available small molecules released by these globally abundant microorganisms.”
Key findings include:
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Substantial contribution to dissolved organic carbon: The identified molecules account for up to 23% of the carbon released by phytoplankton, supporting a significant portion of microbial metabolism in the global ocean.
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Species-specific chemical “menus”: Different phytoplankton species release distinct combinations of metabolites, including carbon compounds containing nitrogen, phosphorus, and sulfur. These chemical variations help shape which microbial communities thrive in different ocean regions.
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Implications for carbon cycling models: Laboratory measurements combined with global ecosystem modeling suggest that phytoplankton-derived metabolites could supply up to 5% of the daily carbon needs of SAR11, one of the most abundant marine bacteria.
“The findings illuminate a long-standing mystery about the composition of the ‘chemical currencies’ that microbes use in the surface ocean,” said Sonya Dyhrman, co-author and professor at Columbia University’s Lamont-Doherty Earth Observatory. “By identifying these compounds, we can begin to build more accurate models of how microbial communities cycle billions of tons of carbon.”
The study was conducted with collaborators from MIT and the Marine Biological Laboratory as part of the National Science Foundation-funded Center for Chemical Currencies of a Microbial Planet, which investigates how small molecules govern microbial interactions across Earth’s ecosystems.
“Understanding these molecular exchanges is critical,” said Elizabeth Kujawinski, WHOI Senior Scientist and center director. “A huge portion of Earth’s carbon cycle passes through this microbial system, yet we still don’t fully understand it. By mapping which molecules phytoplankton release and which molecules bacteria consume, we can start to model the ocean’s microbial network and its role in global carbon cycling.”
Future research will examine how environmental changes—including nutrient availability, temperature fluctuations, and ocean acidification—affect the chemical compounds phytoplankton release and how microbial communities respond to these changes.
