Partitioning of Chromosomal DNA during Establishment of Cellular Asymmetry in Bacillus subtilis

Abstract

The switch from symmetric to asymmetric cell division is a key feature of development in many organisms, including Bacillus subtilis sporulation. Here we demonstrate that, prior to the onset of asymmetric cell division, the B. subtilis chromosome is partitioned into two unequally sized domains, with the origin-proximal one-third of the future forespore chromosome condensed near one pole of the cell. Asymmetric chromosome partitioning is independent of polar division, as it occurs in cells depleted of FtsZ but depends on two transcription factors that govern the initiation of sporulation, σ ^H and Spo0A-P. It is also independent of chromosome partitioning proteins Spo0J and Soj, suggesting the existence of a novel mechanism controlling chromosome structure. Thus, our results demonstrate that, during sporulation, two separable events prepare B. subtilis for asymmetric cell division: the relocation of cell division sites to the cell poles and the asymmetric partitioning of the future forespore chromosome.