Figure 1

The life cycle of Caulobacter crescentus. Swarmer cells are motile, piliated, and unable to initiate DNA replication (in G1, the pre-synthetic gap phase). After an obligatory period spent as non-replicating cells, swarmer cells differentiate into stalked cells. DNA replication and cell division are initiated (in S, the synthesis phase), and the flagellum and pili are replaced by a stalk and an adhesive holdfast. Stalked cells elongate, initiate cell division, and synthesize a new flagellum at the pole opposite the stalked pole. The resulting asymmetric cell produces the two different cell types upon cell separation (at the end of G2, the post-synthetic gap phase). Swarmer cells are unable to initiate DNA replication and cell division until they differentiate, whereas stalked cells can do so immediately after the previous cell division. Immediately after cell separation, the swarmer cell synthesizes pili at the flagellar pole. The timing of various cell-cycle and developmental functions are indicated with boxes and lines, the chromosomes are represented by circles inside the cells for non-replicating chromosomes and by θ structures for replicating chromosomes. Shading indicates the presence of CtrA, and external structures are labeled. Modified from [5].