Chromosome dynamics and spatial organization during the non-binary cell cycle of a predatory bacterium

Abstract

In bacteria, the dynamics of chromosome replication and segregation are tightly coordinated with cell cycle progression, and largely rely on specific spatiotemporal arrangement of the chromosome. Whereas these key processes are mostly investigated in species that divide by binary fission, they remain mysterious in bacteria producing larger number of descendants. Here, we establish the predatory bacterium Bdellovibrio bacteriovorus as a model to investigate the non-binary processing of a circular chromosome. Our data reveal its extreme compaction in a dense polarized nucleoid. We also show that a first binary-like cycle of replication and asymmetric segregation is followed by multiple asynchronous rounds of replication and progressive ParABS-dependent partitioning, uncoupled from cell division. Surprisingly, ParB localization at the centromere is cell-cycle regulated. Altogether, our findings support a model of complex chromosome choreography, leading to the generation of variable numbers of offspring, highlighting the adaptation of conserved mechanisms to achieve non-binary reproduction in bacteria.