Why Aren't All Members of a Species the Same? Exploring the Pangenome

Individual microbes of the same species often have a lot of different genes. But why? (Image: NIAID) Prochlorococcus marinus are diminutive organisms. At less than a micrometer across, these photosynthesizing microbes may be small, but they’re plentiful – by many accounts one of the most abundant species on the planet. But that’s not quite the full story: like any other member of the same species, no two P. marinus individuals are genetically identical. What’s remarkable is how different they may be. Take two different P. marinus cells from different parts of the ocean, sequence their genomes, and lay them side-by-side. Of the approximately 1900 genes that each genome contains, only about 62% are likely to be shared. What makes these two individuals members of the same species is the similarity of one particular gene – the 16S rRNA gene – but the rest of the genome isn’t so consistent. This ...