RocS drives chromosome segregation and nucleoid protection during cell division of Streptococcus pneumoniae

Transregio TRR 174 Seminar

  • Datum: 19.11.2018
  • Uhrzeit: 13:15
  • Vortragende(r): Dr. Christoph Grangeasse
  • CNRS/Université de Lyon, Laboratory of Molecular Microbiology and Structural Biochemistry, France
  • Ort: MPI for Terrestrial Microbiology
  • Raum: Lecture hall
  • Gastgeber: TRR 174
  • Kontakt:

Chromosome segregation in Streptococcus pneumoniae (the pneumococcus) is poorly understood and even less is known about how it is coordinated with other cellular processes. The pneumococcus possesses only the condensin SMC and an incomplete chromosome partitioning ParABS system, in which ParA is absent. Previous studies have evidenced that both ParB and SMC are involved, but not essential, in pneumococcal chromosome segregation. Notably, the double deletion of parB and smc only leads to weak chromosome segregation defects, suggesting that yet uncharacterized factors remain to be identified. Recently, we showed that the tyrosine-autokinase CpsD interferes with chromosome segregation. Indeed, defective autophosphorylation of CpsD hinders cell division, generating elongated cells with an aberrant nucleoid morphology. CpsD is primarily described as a key regulator of the export and synthesis of the polysaccharide capsule, the main virulence factor of the pneumococcus. To further analyze the potential relationship between capsule production and chromosome biology, we sought for CpsD partners. We found a protein of unknown function that is conserved only in Streptococcaceae. This membrane-bound protein, we named RocS (Regulator Of Chromosome Segregation), interacts not only with CpsD but also with DNA and the chromosome partitioning protein ParB. In addition, RocS localizes as foci with a dynamic reminiscent of that of oriC. We also demonstrated that the deletion of rocS drastically alters chromosome segregation, but not replication, and generates anucleate cells. In addition, we observed that the cell elongation resulting from defective autophosphorylation of CpsD is suppressed by the deletion of rocS, abrogating thus the cell division block. Altogether, this work reveals that RocS is a key factor for pneumococcal chromosome segregation. On the other hand, CpsD together with RocS could therefore be viewed as the cornerstone of a nucleoid protection system ensuring proper cell division in coordination with the biogenesis of the protective capsule.

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