Long before plants and algae, cyanobacteria were already performing photosynthesis—filling Earth's skies with oxygen and setting the stage for life as we know it. The ultra-prevalent bacteria are critical to the global carbon cycle, responsible for fixing as much as 30% of the world's carbon dioxide and converting it into oxygen we breathe. And because they're the simplest organisms that carry out this complex process, they're both ideal for studying fundamentals of biology as well as promising contenders for bioengineering.