Biophysical Characterization of ParBS Condensates suggests a physical mechanism for segregation
Year: 2026
Type: preprint
Abstract: The ParABS system orchestrates chromosome segregation in many bacterial species. Centromere-like parS sites nucleate binding of ParB, which subsequently spreads to adjacent non-specific DNA in the presence of CTP. Recruitment of additional ParB molecules and DNA looping via ParB-ParB interactions bring distal chromosome regions into proximity, while interaction with the ParA-ATPase motor drives segregation. In some bacterial species, ParB-parS complexes undergo phase separation into condensates, but their physico-chemical and mechanical properties remain poorly characterized. Turbidity measurements in the presence of CTP, DNA, and physiological mono and divalent salts showed that Mg2+ facilitates condensate formation, whereas K+ concentrations above ∼20 mM disfavor it. Microrheology measurements showed that ParB-parS DNA condensates are viscoelastic, with a room-temperature viscosity of ∼5 Pa·s and a network relaxation time of 0.1 s, allowing rapid responses to deformation. Fluorescence combined with force spectroscopy showed that mechanical disruption of ParB-DNA condensates requires 5-7.5 pN of DNA tension, lower than the force required to stall RNA polymerase but higher than that required for chromosome and plasmid relocation during segregation. These results suggest that ParB-parS condensates dynamically rearrange while maintaining sufficient cohesion to sustain segregation forces without interfering with genomic transactions.
Institutions: Clemson University, University of Pittsburgh, University of Iowa
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7168299925