SMC and the bactofilin/PadC scaffold have distinct yet redundant functions in chromosome segregation and organization in Myxococcus xanthus

Abstract

In bacteria, ParABS systems and structural maintenance of chromosome (SMC) condensin‐like complexes are important for chromosome segregation and organization. The rod‐shaped Myxococcus xanthus cells have a unique chromosome arrangement in which a scaffold composed of the BacNOP bactofilins and PadC positions the essential ParB∙parS segregation complexes and the DNA segregation ATPase ParA in the subpolar regions. We identify the Smc and ScpAB subunits of the SMC complex in M. xanthus and demonstrate that SMC is conditionally essential, with Δsmc or ΔscpAB mutants being temperature sensitive. Inactivation of SMC caused defects in chromosome segregation and organization. Lack of the BacNOP/PadC scaffold also caused chromosome segregation defects but this scaffold is not essential for viability. Inactivation of SMC was synthetic lethal with lack of the BacNOP/PadC scaffold. Lack of SMC interfered with formation of the BacNOP/PadC scaffold while lack of this scaffold did not interfere with chromosome association by SMC. Altogether, our data support that three systems function together to enable chromosome segregation in M. xanthus. ParABS constitutes the basic and essential machinery. SMC and the BacNOP/PadC scaffold have different yet redundant roles in chromosome segregation with SMC supporting individualization of daughter chromosomes and BacNOP/PadC making the ParABS system operate more robustly.

The CTPase activity of ParB determines the size and dynamics of prokaryotic DNA partition complexes

“…The kinetics of ring opening may also affect the DNA-condensing activity observed for some ParB homologs, which is thought to involve bridging interactions between distal ParB dimers (Broedersz et al, 2014;Debaugny et al, 2018;Graham et al, 2014;Sanchez et al, 2013;Song et al, 2017) or non-specific DNA-binding by the C-terminal dimerization domain (Fisher et al, 2017;Taylor et al, 2015). Finally, partition complexes mediate, directly or indirectly, the loading of the SMC/condensin complex (Anand et al, 2020;Bo ¨hm et al, 2020;Gruber and Errington, 2009;Sullivan et al, 2009;Tran et al, 2017). In Corynebacteriumglutamicum, a ParB variant with an amino acid exchange equivalent to R94A in M. xanthus (compare Figure S6C) still recruits SMC to the parS sites but no longer supports its translocation across the chromosome (Bo ¨hm et al, 2020).…”

Catching a Walker in the Act—DNA Partitioning by ParA Family of Proteins

“…In the rod-shaped bacterium Myxococcus xanthus , four bactofilin paralogs have been identified. They serve diverse functions like cell-shape maintenance (Koch et al, 2011 ), cell motility via polar localization of a small GTPase, SofG (Bulyha et al, 2013 ) and chromosome segregation (Lin et al, 2017 ; Anand et al, 2020 ). Three paralogs of bactofilin, BacNOP assemble into a polymeric structure and form a complex with the ParB-like protein, PadC, to restrict ParABS machinery to a well-defined position in the subpolar region of the cell.…”

“…The ParA Mxa ATPase decorates the entire length of the bactofilin filament using the ParB-like adaptor protein PadC. The pole-distal ends of the bactofilin filaments are bound by the centromeric DNA ( parS ) binding protein ParB Mxa ensuring that the genome is equitably transferred after each round of cell division (Lin et al, 2017 ; Anand et al, 2020 ).…”

During heat stress inMyxococcus xanthus, the CdbS PilZ domain protein, along with two PilZ-DnaK chaperones, perturbs chromosome organization and accelerates cell death

“…Segregation also depends on the structural maintenance of chromosome (SMC) complex, which contributes to separating the two daughter chromosomes [32,33]. During segregation, one ParB/parS nucleoprotein complex remains in the subpolar region of the old pole while the second copy translocates to the subpolar region of the opposite pole [29].…”