Take two deep breaths: you can thank phytoplankton for one of them. That’s because these tiny, plant-like organisms produce over half of the oxygen in our atmosphere, most of which comes from our oceans. 

One of the most interesting types of phytoplankton are cyanobacteria. You may recognize the name from the news, because sometimes cyanobacteria become over-abundant in lakes and seas, causing harmful algal blooms. But in the open oceans, they're essential for life. Many cyanobacteria perform photosynthesis. They use special molecular ‘antennae’, called phycobilisomes, that capture energy from sunlight and use it to make sugars for the cells to grow. 

For years, scientists have been looking at ways to culture cyanobacteria in large volumes, for production of biofuels, or even to make buildings from living concrete. But it is not very easy to grow them in large amounts in a lab setting. A group of researchers at the University of Colorado were trying ways to track the growth of a single cyanobacterial cell when they noticed something odd. As the cells multiplied, they would start to grow more and more slowly, so they decided to investigate.

Using specially developed microscopy techniques, the researchers saw that the more cells multiplied, the more they squished their neighbors, until they stopped growing. By measuring the fluorescence of the cells with time-lapse imagery, the team discovered that more squished cells actually stopped photosynthesis. Apparently, when a cell has no more room to grow, it detaches its antennae to shut down photosynthesis! This prevents the cells from growing any larger.

This discovery shows how cyanobacteria have evolved ways to control their growth when caught in a tight spot. In the future, it could help scientists better understand how to grow these organisms in the lab, and how we can use them to make all sorts of renewable resources.