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.