Prochlorococcus Becomes Sticky After Death, Enhancing Oceanic Carbon Export

Recent research indicates that Prochlorococcus – the minute oceanic microbe that generates roughly ten percent of Earth’s oxygen – can enter an unexpectedly sticky state once its growth phase ends, creating microscopic aggregates that may transport carbon down to the deep ocean.

Phytoplankton—tiny plant‑like 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 molecules that underpin marine food chains.

For many years, researchers have characterized Prochlorococcus as a solitary “loner,” since its cells remain free‑floating instead of forming the larger colonies seen in other algae. This isolated lifestyle enables it to dominate extensive ocean regions where light and nutrient competition is intense.

The new study shows that under stress—whether from nutrient shortage, viral attack, or the start of senescence—these cells start releasing adhesive polymers called extracellular polymeric substances. Acting as a natural glue, these compounds cause previously solitary cells to clump into microscopic particles that look like the marine‑snow flakes that sink through the water column.

The resulting aggregates carry significant consequences for the marine carbon cycle. Their increased size and density facilitate transport by currents and gravity beneath the illuminated layer. 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 atmosphere.

Grasping this “second life” of Prochlorococcus improves climate models that depend on predictions of oceanic carbon sequestration. Traditional models have largely viewed Prochlorococcus as a strictly surface‑dwelling organism, 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 sticky behavior be widespread, it may alter current expectations of how marine microbes affect long‑term climate regulation.