Prochlorococcus, the smallest and most abundant photosynthetic organism in the sea, was long considered a free-floating microbe that contributes little to the ocean's biological pump. A team in MIT professor Sallie Chisholm's lab reported in Nature Communications on October 20, 2026, that the organism can also form biofilms — sticky communities of cells attached to surfaces.

In lab cultures, about 6 percent of cells stuck to tube walls, but repeated transfer of only those cells eventually produced populations in which roughly 85 percent were attached. The team's lead author, Maya Anjur-Dietrich, said genetically identical cells can switch between states through gene expression without mutation. Attached cells made more chlorophyll, grew more slowly, and released almost twice as much organic carbon as free-floating cells.

Analyzing seawater DNA, including Tara Oceans data, the team found particle-attached Prochlorococcus in every sample, from sunlit surface waters to 1,000 meters. At Hawaii's Station ALOHA, about 12 percent of the microbial community on particles consisted of Prochlorococcus. The researchers offered a rough first-order estimate that sinking particles could carry about half a billion metric tons of carbon to deeper waters yearly; Anjur-Dietrich stressed the figure is a starting point.