MIT scientists kept growing ocean microbes that clung to test tubes; the sticky share rose from 6% to 85%, revealing a hidden way they release carbon into water

For decades, Prochlorococcus microbes have been shown to live solitary lives in sunlit ocean water. However, according to a 2026 MIT News publication, scientists in the lab of Sallie (Penny) Chisholm at MIT have now found that the microbe can actually form biofilms to live in. The study, titled "Biofilm formation and dynamics in the marine cyanobacterium Prochlorococcus," by Anjur-Dietrich et al., was published as an open-access paper in September 2026 in the journal Nature Communications. The findings could change how scientists view carbon in the world's oceans. Here are the key points.

Small cell, big job

Prochlorococcus is the smallest and most abundant photosynthetic organism in our seas and is responsible for approximately 10% of the carbon taken from the atmosphere by land and oceans every year, per MIT News. According to NOAA’s National Ocean Service, around half of the world’s oxygen is produced by the ocean, mostly by plankton. Most of that ocean-produced oxygen, however, is consumed by marine life itself, and most of what we breathe comes from oxygen that has built up in the atmosphere over hundreds of millions of years. So, Prochlorococcus's real significance lies elsewhere: in carbon capture, not oxygen supply.

The lab had noticed some clues that the organisms were forming biofilms over the years. These clues appeared as clumps of cells forming at the bottom of test tubes containing old cultures. Postdoc Maya Anjur-Dietrich looked in detail at this and found that every strain formed biofilms. In a normal culture, around 6% of the cells were attached; however, when only the attached cells were transferred to fresh media, the attached share rose to around 85% of the population.

Same genome, different mood

You might assume there would have been a mutation to cause them to attach. However, after sequencing, there was no mutation found. Within a given strain, genetically identical cells can switch between being attached or free-floating, it's like having one wardrobe and two completely different outfits. (The exact proportions that switch do vary somewhat from strain to strain, but the switching itself happens without any underlying genetic difference.) Attached cells also had more chlorophyll and slower growth rates. But they released nearly double the dissolved organic carbon into the surrounding water, compared with free-floating cells. Some detached to create new free-floating populations.

Why carbon scientists are interested

The ocean has a biological pump to convert carbon dioxide into organic carbon in sunlit waters, as per the Woods Hole Oceanographic Institution. Much of this carbon sinks to form marine snow. If it can sink deep enough into the ocean, it won’t be mixed back into the atmosphere and can be taken out of circulation for up to thousands of years.

Prochlorococcus was thought to contribute little to the biological pump, as it has a short lifespan in the upper layers of the ocean. That assumption concerns a separate route into the deep ocean from the dissolved-carbon release described above: rather than just releasing carbon into the surrounding water, individual Prochlorococcus cells can physically attach to sinking particles and hitch a ride downward. The team analyzed DNA from seawater, using their own data and the global Tara Oceans Project data bank, and found that Prochlorococcus attached to particles in all samples. These samples ranged from surface waters down to 1,000 meters. Around 12% of the particle-associated microbial community in sunlit waters at Station ALOHA (a research site in Hawaii) was Prochlorococcus.

A big number with an asterisk

If Prochlorococcus can attach to sinking particles, this could result in around half a billion metric tons of carbon being transported to deeper waters every year. However, this is a very crude estimate based on how much Prochlorococcus is present at the surface, how much attaches to particles and how much is consumed, as Anjur-Dietrich mentions.

What’s still unanswered

The team is already looking to see how much of Prochlorococcus overall is particle-associated. Early experiments are looking into whether the attached cells help neighbouring cells and how this affects the rate at which particles degrade. The "loner" label, it turns out, doesn't tell the whole story; even a single species of microbe can hold more than one way of life.