by Merry Youle Bacteria that are born genetically equal aren't necessarily the same. The same genome, residing in cells side-by-side in the same medium in the same flask, does not guarantee the same phenotype. One example that comes to mind is the persisters in E. coli populations—the small number of cells that spontaneously stop growing. If the population is hit by a β-lactam antibiotic, those cells escape death. Similarly, under lab conditions that trigger genetic competence in B. subtilis, only a small fraction of the cells make the switch to competence. B. subtilis cells growing in a rich growth medium offer yet another example. Here genetically identical cells comprise two distinct types. Most are flagellated and actively swimming about as individuals, while a minority have no flagella and form long chains. The game is different in cells in the stationary phase where virtually all of the cells are found in long chains, bound together by an abundant matrix. Losick, Kolter, and colleagues have been working with this system for some years (for earlier papers, click here and here) seeking to determine how such bimodal cell populations are established and maintained in growing cultures.