SMC protein-dependent chromosome condensation during aerial hyphal development in Streptomyces

Members of the SMC (structural maintenance of chromosomes) protein family play a central role in higher-order chromosome dynamics from bacteria to humans. So far, studies of bacterial SMC proteins have focused only on unicellular rod-shaped organisms that divide by binary fission. The conversion of multigenomic aerial hyphae of the mycelial organism Streptomyces coelicolor into chains of unigenomic spores requires the synchronous segregation of multiple chromosomes. Here we focus on the contribution of SMC proteins to sporulation-associated chromosome segregation in S. coelicolor. Deletion of the smc gene causes aberrant DNA condensation and missegregation of chromosomes (7.5% anucleate spores). In vegetative mycelium, immunostained SMC proteins were observed sporadically, while in aerial hyphae about to undergo sporulation they appeared as irregularly spaced foci which accompanied but did not colocalize with ParB complexes. Our data demonstrate that efficient chromosome segregation requires the joint action of SMC and ParB proteins. SMC proteins, similarly to ParAB and FtsZ, presumably belong to a larger group of proteins whose expression is highly induced in response to the requirement of aerial hyphal maturation.