Société Française de Biochimie et Biologie Moléculaire

Chryslène MERCY - August 2019

Molecular Microbiology and Structural Biochemistry, UMR 5086, Université Claude Bernard Lyon 1, CNRS, Lyon RocS drives chromosome segregation and nucleoid protection in Streptococcus pneumoniae Nature Microbiology June 2019 Mercy, A Ducret, J Slager, J-P Lavergne, C Freton, S N Nagarajan, P-S Garcia, M-F Noirot-Gros, N Dubarry, J Nourikyan, J-W Veening & C Grangeasse


After a Master's degree in Microbiology and Biotechnology from the University of Marseille, Chryslène MERCY (29 years old) defended her pHD entitled "Regulation of the cell cycle of the pathogenic bacterium Streptococcus pneumoniae by tyrosine kinase CpsD and the serine / threonine kinase StkP" under the supervision of Dr. Christophe Grangeasse (Laboratory of Molecular Microbiology and Structural Biochemistry, University of Lyon). Her work focused on the characterization of the regulatory mechanisms by phosphorylation of different aspects of the bacterial cell cycle such as cell division, morphogenesis and chromosome segregation of this pathogenic bacterium. In the selected article published in Nature Microbiology (issue of June 2019), Chrystèle and co-workers identified a protein of unknown function (RocS for Regulator Of ChromosomeSegregation) and characterized its role in chromosome segregation and nucleoid protection.



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Segregation of replicated chromosomes in bacteria is poorly understood outside someprominent 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 cell division protein FtsZ and 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 a nucleoid protection system ensuring proper cell division in coordination with the biogenesis of a protective capsular layer.