The bacterial cell cycle: correlations and causation
How cells regulate the timing of cell division and the initiation of new rounds of DNA replication is a longstanding problem. In recent years, new models of cell size homeostasis have been proposed for bacteria, yeast and mammalian cells. A common method to test such models has been to compare the correlations predicted by them to those experimentally measured (e.g., the correlation of cell size at birth and division or the generation time). However, distinct models may predict identical sets of correlation coefficients. I will show that using conditional independence tests (considering the correlation of a pair of variables conditioned on a third) provides new insights into the problem. We find that for E. coli replication is tightly coupled to division in slow growth conditions while in fast growth conditions the division event is influenced by additional processes.