Chromosome segregation dynamics during the cell cycle of Staphylococcus aureus

Research on chromosome organization and cell cycle progression in spherical bacteria, particularly Staphylococcus aureus, remains limited and fragmented. In this study, we established a working model to investigate chromosome dynamics in S. aureus using a Fluorescent Reporter Operator System (FROS), which enabled precise localization of specific chromosomal loci. This approach revealed that the S. aureus cell cycle and chromosome replication cycle are not coupled, with cells exhibiting two segregated origins of replication at the start of the cell cycle. The chromosome has a specific origin-terminus-origin conformation, with origins localizing near the membrane, towards the tip of each hemisphere, or the “cell poles”. We further used this system to assess the role of various proteins with a role in S. aureus chromosome biology, focusing on the ParB-parS and SMC-ScpAB systems. Our results demonstrate that ParB binds five parS chromosomal sequences and the resulting complexes influence chromosome conformation, but play a minor role in chromosome compaction and segregation. In contrast, the SMC-ScpAB complex plays a key role in S. aureus chromosome biology, contributing to chromosome compaction, segregation and spatial organization. Additionally, we systematically assessed the impact of proteins linking chromosome segregation to cell division—Noc, FtsK, SpoIIIE, and XerC—on origin and terminus number and positioning. While these proteins have been studied previously, our work uniquely standardizes comparisons by using the same strain background, growth conditions, and analytical approaches for all mutants. This work provides a comprehensive study of the factors governing chromosome dynamics and organization in S. aureus, contributing to our knowledge on chromosome biology of spherical bacteria. Hi-C and whole genome sequencing expriments were performed on wild type and mutant cells of Staphylococcus aureus JE2 growing in TSB.