Christophe Grangeasse, Director of Research, Laboratory of Molecular Microbiology & Structural Biochemistry, CNRS, Universite de Lyon, France, will give a seminar on "Coordination of cell division, chromosome segregation and capsule assembly in Streptococcus pneumoniae."

ABSTRACT

A particular class of tyrosine-autokinases is widespread among all bacterial phyla. These enzymes, called BY-kinases for Bacterial tYrosine-kinases, are crucial for the assembly of the polysaccharide capsule. Interestingly, BY-kinases possess a structural fold comparable to that of ParA proteins that usually assist ParB in chromosome segregation. We previously showed that the BY-kinase CpsD not only regulates the assembly of the polysaccharide capsule but also interferes with chromosome segregation and cell division of Streptococcus pneumoniae. Indeed, defective autophosphorylation of CpsD hinders cell division, generating elongated cells with an aberrant nucleoid morphology. To further analyze the potential relationship between capsule production and the 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 also with the DNA and the chromosome partitioning protein ParB. We also demonstrated that the deletion of rocS drastically alters chromosome segregation. 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 the cornerstone of a new nucleoid protection system ensuring proper chromosome segregation and cell division in coordination with capsule production.