RocS drives chromosome segregation and nucleoid occlusion in Streptococcus pneumoniae

Segregation of replicated chromosomes in bacteria is poorly understood outside some prominent model strains and even less is known about how it is coordinated with other cellular processes. Here we report that RocS is crucial for chromosome segregation in the opportunistic human pathogen Streptococcus pneumoniae. RocS is membrane-bound and interacts both with DNA and the chromosome partitioning protein ParB to properly segregate the origin of replication region to new daughter cells. In addition, we show that RocS interacts with the tyrosine-autokinase CpsD required for polysaccharide capsule biogenesis, which is crucial for S. pneumoniae's ability to prevent host immune detection. Altering the RocS-CpsD interaction drastically hinders chromosome partitioning and cell division. Altogether, this work reveals that RocS is the cornerstone of an atypical nucleoid occlusion system ensuring proper cell division in coordination with the biogenesis of a protective capsular layer.