Prochlorococcus Turns Sticky After Life, Boosting Ocean Carbon Transfer

A new study has shown that Prochlorococcus, the tiny marine microbe responsible for about one‑tenth of the planet's oxygen, can adopt a surprisingly adhesive mode after its active phase, forming microscopic clumps that may help ferry carbon to the deep sea.

Phytoplankton—microscopic plants that drift in the sunlit surface waters—produce the oxygen in roughly every other breath we take. Among them, Prochlorococcus stands out as the smallest and most plentiful photosynthetic organism on Earth, thriving in nutrient‑poor tropical waters and converting sunlight into carbon‑rich compounds that form the base of marine food webs.

For decades, scientists have described Prochlorococcus as a solitary “loner,” largely because its cells float independently rather than assembling into the larger colonies typical of other algae. This solitary habit allows it to dominate vast oceanic expanses where competition for light and nutrients is fierce.

The recent research reveals that when the cells encounter stress—such as nutrient depletion, viral infection, or the onset of senescence—they begin to excrete sticky polymers known as extracellular polymeric substances. These substances act like natural glue, causing the once‑isolated cells to aggregate into microscopic particles that resemble the marine‑snow flakes that drift downward.

These newly formed aggregates have important implications for the ocean’s carbon cycle. By clumping together, the cells increase in size and density, making it easier for ocean currents and gravity to pull them below the sunlit zone. As they sink, they transport the carbon they captured during photosynthesis into the deep ocean, where it can be stored for centuries, effectively removing CO₂ from the atmosphere.

Understanding this “second life” of Prochlorococcus helps refine climate models that rely on estimates of how much carbon the ocean can sequester. Existing models have largely treated Prochlorococcus as a purely surface‑bound player, but the discovery of its sticky phase suggests a more dynamic contribution to carbon export.

Researchers plan to monitor the prevalence of these aggregates in different ocean regions and to integrate the findings into global biogeochemical simulations. If the sticky behavior proves widespread, it could reshape expectations for how marine microbes influence long‑term climate regulation.