As much as 40% of the carbon in Earth's atmosphere gets squirreled away, at least temporarily, by cyanobacteria, the blue-green algae that permeate the oceans. How do they trap so much carbon? Researchers stained the algae with a fluorescent dye that targets carbon-containing proteins. The resulting pattern of green spots seen in this picture reveal that the organisms hold the carbon inside tiny compartments called carboxysomes, which are arranged in a straight line inside each cell. For reasons not yet fully understood, the alignment allows the bacteria to pack away a large amount of carbon easily, the researchers report tomorrow in Science. When the team modified the microbes to disrupt the straight-line pattern of the caroxysomes, their ability to sequester carbon plummeted.