SMC ensures efficient chromosome replication and oriC positioning during Streptomyces spore germination

Abstract Bacterial chromosomes are organized by condensins, such as Structural Maintenance of Chromosomes (SMC) proteins. In Streptomyces, a genus of sporulating bacteria, SMC proteins align chromosomal arms and promote efficient compaction of chromosomal DNA during spore formation. We hypothesized that disrupting nucleoid architecture by deleting the smc gene would affect the positioning of the origin of replication (oriC) or the process of chromosome replication during spore germination. To test this hypothesis, we conducted marker frequency analyses and microscopy studies to observe the positioning of labelled oriC and replisomes in both wild type and Δsmc backgrounds. Additionally, we investigated the positioning of three chromosomal loci in early vegetative cells. Our results indicate that the deletion of smc impairs chromosome replication and hinders germ tube development. Furthermore, detailed analysis of chromosome organization revealed that, in the absence of SMC, the oriC region becomes mispositioned within the nucleoid. These findings underscore the important role of SMC in maintaining nucleoid architecture during the early growth stages of Streptomyces.