SMC and the bactofilin/PadC scaffold have distinct yet redundant functions in chromosome segregation and organization in Myxococcus xanthus
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 three bactofilins (BacNOP) and PadC positions the essential ParB{middle dot}parS segregation complexes and the DNA segregation ATPase ParA in the subpolar regions. Here, we identify the Smc and ScpAB subunits of the SMC complex in M. xanthus and demonstrate that SMC is conditionally essential with mutants containing smc or scpAB deletions being temperature sensitive. Lack of SMC caused defects in chromosome segregation and organization. Lack of the BacNOP/PadC scaffold caused chromosome segregation defects but was not essential. 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 cooperate to enable chromosome segregation in M. xanthus, whereby ParABS constitutes the basic machinery and SMC and the BacNOP/PadC scaffold have distinct yet redundant roles in this process with SMC supporting individualization of daughter chromosomes and BacNOP/PadC making the ParABS system operate more robustly