Simultaneous regulation of size and DNA replication in bacteria

In rich nutrient conditions, bacterial cells may divide faster than their chromosomes replicate, implying that cells maintain multiple rounds of chromosome replication. I will show that both cell size and chromosome replication may be simultaneously regulated by following a simple control mechanism, in which, effectively, a constant volume is added between two DNA replication initiation events per each origin of replication. This model elucidates the experimentally observed correlations between various events in the cell cycle, and explains the exponential dependence of cell size on the growth rate. Finally, I will show some analogous results for budding yeast and archaeal cell growth, as well as analysis of experiments where bacterial cell morphology is perturbed.