Excitable dynamics of ParA during bacterial cell division

ParABS system is a conserved machinery that drives the partitions of genome and other large intracellular cargos in bacteria. It works as a ParA concentration-based Brownian ratchet, which ensures the partition fidelity by operating at the critical point in its parameter space and localizing the ParA nearby to buffer against the large fluctuations in the ParA intracellular concentration. Despite these progresses, our understanding of the ParABS-driven partition mechanism remains incomplete. It is not understood what causes the large cell-to-cell fluctuation in the ParA intracellular concentration and why the bacterium cannot minimize this noise to better control the partition fidelity. We present experimental evidence with low-copy-number F-plasmids in E. coli that ParA robustly oscillates from pole to pole along the nucleoid length, underlying the observed large fluctuations in ParA intracellular concentration. Our theory-experiment synergy demonstrates that the ParA oscillation hinges on the nucleoid dimension and the ParB-mediated negative feedback with ParA in nucleoid binding. We suggest that the low-copy-number plasmid manages its partition fidelity with “autonomy”: The plasmid harnesses the same ParB-mediated negative feedback – that dissociates the ParA from the nucleoid underneath the plasmid – to maintain the nucleoid-bound ParA at a proper level further away. And the ParA oscillation is reminiscent of this underlying feedback mechanism, which adapts the partition fidelity to the nucleoid growth. Our work may provide an overarching framework of intracellular partitioning in bacteria. Significance Statement ParABS system is a conserved partition machinery for genome and other large cargos inside bacteria and works as a ParA concentration-based Brownian ratchet. It operates at the critical point in parameter space for sensitive adaptation and localizes the ParA nearby to buffer against the large cell-to-cell ParA concentration variations evidenced in bacteria. Why cannot the bacterium minimize this noise to better control the partition fidelity? Hereby, we showed that the large cell-to-cell ParA concentration variations stem from the ParA pole-to-pole oscillations along the nucleoid length and embodies an automony strategy that the intracellular cargo controls the nucleoid-bound ParA at a proper level to ensures its partition fidelity. Our work may provide an overarching framework of intracellular partitioning in bacteria.