Know more

For decades, scientists believed that the rigid wall surrounding bacterial cells (prokaryotes) was the only shape-determining factor. In higher organisms (eukaryotes), cells have a meshwork of protein filaments, particularly actin filaments, which control cellular shape. This complex meshwork is known as the “cytoskeleton”. More recently, it has been shown that bacteria also have a dynamic cytoskeleton involved in the spatial organization of processes essentially associated with cellular growth.

In this fundamental research project, we propose to study the actin cytoskeleton (encoded by the mre genes) during the development, in stationary phase, of competence and sporulation, the two main environmental adaptations in the model organism Bcillus subtilis. The development of these two processes, which have been studied for more than 80 years, requires a large reorganization of gene expression, protein localization but also of cell shape in B. subtilis. Because they are energetically costly, these physiological adaptations impose a growth arrest. However, it has been shown that the expression of the mre genes is activated during the development of competence or sporulation. But why are the actin cytoskeleton genes, which are among the major cellular growth determinants controlling peptidoglycan synthesis, induced while the cells have stopped dividing?

In this research project, we propose a multi disciplinary approach (transcriptional regulation, microscopy, biochemistry) in order to characterize the organization, the eventual restructuring and the functions of the actin cytoskeleton in stationary phase. For example, I will bring my expertise in the use of the luciferase of Photinus pyralys as a transcriptional reporter in order to study the expression profiles of the cytoskeleton genes in different media or genetic backgrounds. In addition, the host laboratory, which is a leader in the description and comprehension of the roles of the actin cytoskeleton in the prokaryotes, has mastered several advanced microscopy techniques (TIRFM, microfluidic) allowing the optimal visualization of the bacterial cytoskeleton. Finally, several techniques allowing the identification of protein-protein interactions will be possible, in situ, in the lab or the department, in order to establish eventual links between cytoskeleton and competence or sporulation.

1- Genome Sequence of the Bacillus subtilis Biofilm-Forming Transformable Strain PS216.
Durrett R, Miras M, Mirouze N, Narechania A, Mandic-Mulec I, Dubnau D.

Genome Announc. 2013 Jun 20;1(3). doi:pii: e00288-13. 10.1128/genomeA.00288-13.

2- Direct involvement of DprA, the transformation-dedicated RecA loader, in the shut-off of pneumococcal competence.
Mirouze N*, Bergé MA*, Soulet AL, Mortier-Barrière I, Quentin Y, Fichant G, Granadel C, Noirot-Gros MF, Noirot P, Polard P, Martin B, Claverys JP.

Proc Natl Acad Sci U S A. 2013 Mar 12;110(11):E1035-44. doi: 10.1073/pnas.1219868110. Epub 2013 Feb 25.

3- ComE/ComE~P interplay dictates activation or extinction status of pneumococcal X-state (competence).
Martin B*, Soulet AL*, Mirouze N*, Prudhomme M, Mortier-Barrière I, Granadel C, Noirot-Gros MF, Noirot P, Polard P, Claverys JP.

Mol Microbiol. 2013 Jan;87(2):394-411. doi: 10.1111/mmi.12104. Epub 2012 Dec 10.

4- Structure-function analysis of pneumococcal DprA protein reveals that dimerization is crucial for loading RecA recombinase onto DNA during transformation.
Quevillon-Cheruel S*, Campo N*, Mirouze N*, Mortier-Barrière I, Brooks MA, Boudes M, Durand D, Soulet AL, Lisboa J, Noirot P, Martin B, van Tilbeurgh H, Noirot-Gros MF, Claverys JP, Polard P.

Proc Natl Acad Sci U S A. 2012 Sep 11;109(37):E2466-75. doi: 10.1073/pnas.1205638109. Epub 2012 Aug 17.

5- Spo0A~P imposes a temporal gate for the bimodal expression of competence in Bacillus subtilis.
Mirouze N, Desai Y, Raj A, Dubnau D.

PLoS Genet. 2012;8(3):e1002586. doi: 10.1371/journal.pgen.1002586. Epub 2012 Mar 8.

6- An atypical Phr peptide regulates the developmental switch protein RapH.
Mirouze N, Parashar V, Baker MD, Dubnau DA, Neiditch MB.

J Bacteriol. 2011 Nov;193(22):6197-206. doi: 10.1128/JB.05860-11. Epub 2011 Sep 9.

7- Fluctuations in spo0A transcription control rare developmental transitions in Bacillus subtilis.
Mirouze N, Prepiak P, Dubnau D.

PLoS Genet. 2011 Apr;7(4):e1002048. doi: 10.1371/journal.pgen.1002048. Epub 2011 Apr 28.

8- MecA dampens transitions to spore, biofilm exopolysaccharide and competence expression by two different mechanisms.
Prepiak P, Defrancesco M, Spadavecchia S, Mirouze N, Albano M, Persuh M, Fujita M, Dubnau D.

Mol Microbiol. 2011 May;80(4):1014-30. doi: 10.1111/j.1365-2958.2011.07627.x. Epub 2011 Apr 11.

9- Structural basis of response regulator dephosphorylation by Rap phosphatases.
Parashar V, Mirouze N, Dubnau DA, Neiditch MB.

PLoS Biol. 2011 Feb 8;9(2):e1000589. doi: 10.1371/journal.pbio.1000589.

10- A key presynaptic role in transformation for a widespread bacterial protein: DprA conveys incoming ssDNA to RecA.
Mortier-Barrière I*, Velten M, Dupaigne P*, Mirouze N*, Piétrement O, McGovern S, Fichant G, Martin B, Noirot P, Le Cam E, Polard P, Claverys JP.

Cell. 2007 Sep 7;130(5):824-36.
* These authors contributed equally.