Simultaneous regulation of cell size and chromosome replication in bacteria

TL;DR

This paper demonstrates that bacteria regulate cell size and chromosome replication simultaneously through a model based on initiator accumulation, explaining observed cell cycle correlations and size control mechanisms.

Contribution

It introduces a unified model linking initiator accumulation to both cell size regulation and chromosome replication timing in bacteria.

Findings

Model reproduces experimental cell cycle correlations

Explains exponential size dependence on growth rate

Aligns with observed regulation of replication origins

Abstract

Bacteria are able to maintain a narrow distribution of cell sizes by regulating the timing of cell divisions. In rich nutrient conditions, cells divide much faster than their chromosomes replicate. This implies that cells maintain multiple rounds of chromosome replication per cell division by regulating the timing of chromosome replications. Here, we show that both cell size and chromosome replication may be simultaneously regulated by the long-standing initiator accumulation strategy. The strategy proposes that initiators are produced in proportion to the volume increase and is accumulated at each origin of replication, and chromosome replication is initiated when a critical amount per origin has accumulated. We show that this model maps to the incremental model of size control, which was previously shown to reproduce experimentally observed correlations between various events in the cell cycle and explains the exponential dependence of cell size on the growth rate of the cell. Furthermore, we show that this model also leads to the efficient regulation of the timing of initiation and the number of origins consistent with existing experimental results.