Microbial manners on the high seas

A new study found that microbes in the Sargasso Sea divide nutrients throughout their communities over time, supporting coexistence and efficient nutrient use in nutrient-limited environments.

The study, whose co-authors included University of Tennessee Kenneth and Blaire Mossman Professor in microbiology Steven Wilhelm and University of Maryland mathematical modeling professor Joshua Weitz, showed that phytoplankton and other microbes in the Atlantic Ocean's Sargasso Sea take turns using phosphorus, a critical nutrient for their growth but one that remains scarce in this region. The study was published in March in Proceedings of the National Academy of Sciences (PNAS).

“The study demonstrates a manifestation of a classic ecological strategy—temporal resource partitioning—occurring in a complex microbial community,” said Wilhelm. “By assimilating nutrient resources at different times of day, the microorganisms in this oligotrophic region, effectively an oceanic desert, avoid competition between species.”

Larger organisms, like birds, sharks, or fish, have exhibited this type of timed feeding schedule before, but only recently has this concept been apparent in natural microbial systems.

“It illustrates how organisms can coexist in the face of severe nutrient limitation,” said Wilhelm.

The research team includes Wilhelm; Weitz; UT Research Assistant Professor Gary LeCleir; UT microbiology alumni Lena Pound and Naomi Gilbert; and Daniel Muratore, a postdoctoral fellow at the Santa Fe Institute and a former student of Weitz.

Their work addresses a decades-old question raised by ecologist G. Evelyn Hutchinson: Why do so many phytoplankton species exist? Mathematically, the huge, teeming populations of these photosynthesizing bacteria should not all survive while competing for limited nutrients. The phenomenon is known as “the paradox of the plankton.”

Their new evidence adds further support to the theory that the plankton feed at different times of the day—a process called temporal niche partitioning. They found evidence of this among plankton in a long-term study site in the North Atlantic Ocean, which echoes a previous study co-authored by Weitz that showed similar activity by plankton in the north Pacific Ocean.

“We went to a completely different ocean, did a comparable study and found the same signature of temporal niche partitioning for phosphorus as we did for nitrogen,” said joint first author Muratore. “This suggests that reducing competition by taking turns might be a general feature of maintaining biodiversity in the ocean microbiome.”

Their research reveals the complex interplay between the billions of microbes that share limited resources in a single liter of ocean water. Their findings may indicate that these microbes coevolved together, influencing each other to develop compatible strategies for nutrient uptake.

Understanding how plankton consume phosphorus— a key component of RNA, DNA, cell membranes, and energy storage—can help predict how ocean life will respond to changing climate conditions. The methods in this study could help other researchers studying similar habits in species worldwide.

“We have developed computational methods to parse a large amount of cellular activity data in ways that can help others identify when microbes limit competition with one another,” Weitz said. “It’s really exciting to get a glimpse of principles that may help sustain diverse microbial life in the global oceans.”