The great divide: coordinating cell cycle events during bacterial growth and division

Abstract

The relationship between events during the bacterial cell cycle has been the subject of frequent debate. While early models proposed a relatively rigid view in which DNA replication was inextricably coupled to attainment of a specific cell mass, and cell division was triggered by the completion of chromosome replication, more recent data suggest these models were oversimplified. Instead, an intricate set of intersecting, and at times opposing, forces coordinate DNA replication, cell division, and cell growth with one another, thereby ensuring the precise spatial and temporal control of cell cycle events.

Figure 1. The bacterial cell cycle

In slow-growing bacteria, the cell cycle is divided into three well-defined periods: i) the B-period – birth to the initiation of DNA replication, ii) the C-period – replication initiation through termination, and iii) the D-period – termination to division. Separation of sister chromosomes occurs concurrently with DNA replication. The origin region is indicated by a red dot. The cytokinetic ring (green) assembles sometime after the initiation of DNA replication, however, division does not occur until nucleoid segregation is complete. The B-period is nonexistent in fast-growing cells in which generation times are less than or equal to the time required for replication and division.

Figure 2. Multiple points of coordination exist between cell cycle events

Arrows indicate the direction of influence in coordination. Some interactions have been demonstrated experimentally while others are inferred.