Chromosome choreography during the non-binary cell cycle of a predatory bacterium

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. We found that its single chromosome is highly compacted in a polarized nucleoid that excludes freely diffusing proteins during the non-proliferative stage of the cell cycle. A binary-like cycle of DNA replication and asymmetric segregation is followed by multiple asynchronous rounds of replication and progressive ParABS-dependent partitioning, uncoupled from cell division. Finally, we provide the first evidence for an on-off behavior of the ParB protein, which localizes at the centromere in a cell-cycle-regulated manner. Altogether, our findings support a model of complex chromosome choreography leading to the generation of variable, odd, or even numbers of offspring and highlight the adaptation of conserved mechanisms to achieve non-binary reproduction. [Display omitted] •The Bdellovibrio chromosome is polarized, with ori located near the invasive pole•The highly compacted nucleoid excludes cytosolic proteins in non-replicative cells•Replication and segregation of chromosomes are uncoupled from cell division•The centromeric protein ParB localizes at parS in a cell-cycle-dependent manner Kaljević et al. study non-binary proliferation in the predatory bacterium Bdellovibrio bacteriovorus. Examination of the spatiotemporal dynamics of its DNA throughout the cell cycle reveals that, as the predator elongates, concomitant rounds of replication and segregation generate chromosome copies for more than two daughter cells.