Genomics reveals alga-associated cyanobacteria hiding in plain sight

Cyanobacteria occupy a special place in the pantheon of prokaryotic life. It is in the ancestors of these ubiquitous microbes that oxygenic photosynthesis first evolved more than 2 billion y ago (1), and it is from endosymbiotic cyanobacteria that the plastids (chloroplasts) of plants and algae are derived (2). Modern-day cyanobacteria are diverse in form and function; they include coccoid marine picoplankton such as Prochlorococcus (3),...