Professor Sallie Chisholm and former postdoctoral associate Nadav Kashtan performed a cell-by-cell genomic analysis on a wild population of the marine microbe Prochlorococcus living in a milliliter — less than a quarter teaspoon — of ocean water, and found hundreds of distinct genetic subpopulations. Each subpopulation is characterized by a set of core gene alleles linked to a few flexible genes — a combination the CEE scientists call the “genomic backbone” — that endows the subpopulation with a finely tuned suitability for a particular ecological niche. Read a news story.