Prochlorococcus Becomes Adhesive After Death, Enhancing Deep‑Ocean Carbon Transfer

Recent research demonstrates that Prochlorococcus, the minute oceanic microbe that generates roughly ten percent of Earth’s oxygen, can switch to an unexpectedly sticky state once its growth phase ends, creating microscopic aggregates that could transport carbon to the ocean depths.

Phytoplankton—tiny photosynthetic organisms floating in sunlit surface waters—supply the oxygen in about half of each breath we inhale. Within this group, Prochlorococcus is the tiniest and most abundant photosynthesizer on the planet, flourishing in nutrient‑scarce tropical seas and turning sunlight into carbon‑rich substances that underpin marine food chains.

For many years researchers have labeled Prochlorococcus a solitary “loner,” since its cells remain free‑floating instead of forming the larger colonies seen in other algae. This independent lifestyle lets it prevail across extensive ocean regions where light and nutrients are hotly contested.

The new study finds that under stress—whether from nutrient shortage, viral attack, or the start of senescence—these cells start secreting sticky polymers called extracellular polymeric substances. Acting as a natural adhesive, these compounds cause formerly solitary cells to cluster into microscopic particles reminiscent of the marine‑snow flakes that sink.

The resulting aggregates carry significant consequences for the marine carbon cycle. Their combined size and density enable ocean currents and gravity to draw them beneath the photic layer more readily. As they descend, they convey the carbon fixed during photosynthesis into the deep sea, where it may remain sequestered for centuries, thereby extracting CO₂ from the air.

Grasping this “second life” of Prochlorococcus aids in sharpening climate models that depend on projections of oceanic carbon storage. Traditional models have largely considered Prochlorococcus a strictly surface‑dwelling actor, yet the identification of its adhesive stage points to a more active role in carbon export.

Scientists intend to track the occurrence of these aggregates across various oceanic zones and to incorporate the data into worldwide biogeochemical simulations. Should the adhesive behavior be widespread, it may alter forecasts of how marine microbes affect long‑term climate regulation.